3 files changed, 1683 insertions, 11 deletions

diff --git a/kernel/events/Makefile b/kernel/events/Makefile
index 22d901f9caf4..103f5d147b2f 100644
--- a/kernel/events/Makefile
+++ b/kernel/events/Makefile
@@ -3,4 +3,7 @@ CFLAGS_REMOVE_core.o = -pg
 endif
 
 obj-y := core.o ring_buffer.o callchain.o
+
 obj-$(CONFIG_HAVE_HW_BREAKPOINT) += hw_breakpoint.o
+obj-$(CONFIG_UPROBES) += uprobes.o
+
diff --git a/kernel/events/core.c b/kernel/events/core.c
index a6a9ec4cd8f5..d7d71d6ec972 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -253,9 +253,9 @@ perf_cgroup_match(struct perf_event *event)
         return !event->cgrp || event->cgrp == cpuctx->cgrp;
 }
 
-static inline void perf_get_cgroup(struct perf_event *event)
+static inline bool perf_tryget_cgroup(struct perf_event *event)
 {
-        css_get(&event->cgrp->css);
+        return css_tryget(&event->cgrp->css);
 }
 
 static inline void perf_put_cgroup(struct perf_event *event)
@@ -484,7 +484,11 @@ static inline int perf_cgroup_connect(int fd, struct perf_event *event,
         event->cgrp = cgrp;
 
         /* must be done before we fput() the file */
-        perf_get_cgroup(event);
+        if (!perf_tryget_cgroup(event)) {
+                event->cgrp = NULL;
+                ret = -ENOENT;
+                goto out;
+        }
 
         /*
          * all events in a group must monitor
@@ -3181,9 +3185,8 @@ static void perf_event_for_each(struct perf_event *event,
         event = event->group_leader;
 
         perf_event_for_each_child(event, func);
-        func(event);
         list_for_each_entry(sibling, &event->sibling_list, group_entry)
-                perf_event_for_each_child(event, func);
+                perf_event_for_each_child(sibling, func);
         mutex_unlock(&ctx->mutex);
 }
 
@@ -4957,7 +4960,7 @@ void __perf_sw_event(u32 event_id, u64 nr, struct pt_regs *regs, u64 addr)
         if (rctx < 0)
                 return;
 
-        perf_sample_data_init(&data, addr);
+        perf_sample_data_init(&data, addr, 0);
 
         do_perf_sw_event(PERF_TYPE_SOFTWARE, event_id, nr, &data, regs);
 
@@ -5215,7 +5218,7 @@ void perf_tp_event(u64 addr, u64 count, void *record, int entry_size,
                 .data = record,
         };
 
-        perf_sample_data_init(&data, addr);
+        perf_sample_data_init(&data, addr, 0);
         data.raw = &raw;
 
         hlist_for_each_entry_rcu(event, node, head, hlist_entry) {
@@ -5318,7 +5321,7 @@ void perf_bp_event(struct perf_event *bp, void *data)
         struct perf_sample_data sample;
         struct pt_regs *regs = data;
 
-        perf_sample_data_init(&sample, bp->attr.bp_addr);
+        perf_sample_data_init(&sample, bp->attr.bp_addr, 0);
 
         if (!bp->hw.state && !perf_exclude_event(bp, regs))
                 perf_swevent_event(bp, 1, &sample, regs);
@@ -5344,13 +5347,12 @@ static enum hrtimer_restart perf_swevent_hrtimer(struct hrtimer *hrtimer)
 
         event->pmu->read(event);
 
-        perf_sample_data_init(&data, 0);
-        data.period = event->hw.last_period;
+        perf_sample_data_init(&data, 0, event->hw.last_period);
         regs = get_irq_regs();
 
         if (regs && !perf_exclude_event(event, regs)) {
                 if (!(event->attr.exclude_idle && is_idle_task(current)))
-                        if (perf_event_overflow(event, &data, regs))
+                        if (__perf_event_overflow(event, 1, &data, regs))
                                 ret = HRTIMER_NORESTART;
         }
 
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
new file mode 100644
index 000000000000..985be4d80fe8
--- /dev/null
+++ b/kernel/events/uprobes.c
@@ -0,0 +1,1667 @@
+/*
+ * User-space Probes (UProbes)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (C) IBM Corporation, 2008-2012
+ * Authors:
+ *      Srikar Dronamraju
+ *      Jim Keniston
+ * Copyright (C) 2011-2012 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
+ */
+
+#include <linux/kernel.h>
+#include <linux/highmem.h>
+#include <linux/pagemap.h>      /* read_mapping_page */
+#include <linux/slab.h>
+#include <linux/sched.h>
+#include <linux/rmap.h>         /* anon_vma_prepare */
+#include <linux/mmu_notifier.h> /* set_pte_at_notify */
+#include <linux/swap.h>         /* try_to_free_swap */
+#include <linux/ptrace.h>       /* user_enable_single_step */
+#include <linux/kdebug.h>       /* notifier mechanism */
+
+#include <linux/uprobes.h>
+
+#define UINSNS_PER_PAGE                 (PAGE_SIZE/UPROBE_XOL_SLOT_BYTES)
+#define MAX_UPROBE_XOL_SLOTS            UINSNS_PER_PAGE
+
+static struct srcu_struct uprobes_srcu;
+static struct rb_root uprobes_tree = RB_ROOT;
+
+static DEFINE_SPINLOCK(uprobes_treelock);       /* serialize rbtree access */
+
+#define UPROBES_HASH_SZ 13
+
+/* serialize (un)register */
+static struct mutex uprobes_mutex[UPROBES_HASH_SZ];
+
+#define uprobes_hash(v)         (&uprobes_mutex[((unsigned long)(v)) % UPROBES_HASH_SZ])
+
+/* serialize uprobe->pending_list */
+static struct mutex uprobes_mmap_mutex[UPROBES_HASH_SZ];
+#define uprobes_mmap_hash(v)    (&uprobes_mmap_mutex[((unsigned long)(v)) % UPROBES_HASH_SZ])
+
+/*
+ * uprobe_events allows us to skip the uprobe_mmap if there are no uprobe
+ * events active at this time.  Probably a fine grained per inode count is
+ * better?
+ */
+static atomic_t uprobe_events = ATOMIC_INIT(0);
+
+/*
+ * Maintain a temporary per vma info that can be used to search if a vma
+ * has already been handled. This structure is introduced since extending
+ * vm_area_struct wasnt recommended.
+ */
+struct vma_info {
+        struct list_head        probe_list;
+        struct mm_struct        *mm;
+        loff_t                  vaddr;
+};
+
+struct uprobe {
+        struct rb_node          rb_node;        /* node in the rb tree */
+        atomic_t                ref;
+        struct rw_semaphore     consumer_rwsem;
+        struct list_head        pending_list;
+        struct uprobe_consumer  *consumers;
+        struct inode            *inode;         /* Also hold a ref to inode */
+        loff_t                  offset;
+        int                     flags;
+        struct arch_uprobe      arch;
+};
+
+/*
+ * valid_vma: Verify if the specified vma is an executable vma
+ * Relax restrictions while unregistering: vm_flags might have
+ * changed after breakpoint was inserted.
+ *      - is_register: indicates if we are in register context.
+ *      - Return 1 if the specified virtual address is in an
+ *        executable vma.
+ */
+static bool valid_vma(struct vm_area_struct *vma, bool is_register)
+{
+        if (!vma->vm_file)
+                return false;
+
+        if (!is_register)
+                return true;
+
+        if ((vma->vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)) == (VM_READ|VM_EXEC))
+                return true;
+
+        return false;
+}
+
+static loff_t vma_address(struct vm_area_struct *vma, loff_t offset)
+{
+        loff_t vaddr;
+
+        vaddr = vma->vm_start + offset;
+        vaddr -= vma->vm_pgoff << PAGE_SHIFT;
+
+        return vaddr;
+}
+
+/**
+ * __replace_page - replace page in vma by new page.
+ * based on replace_page in mm/ksm.c
+ *
+ * @vma:      vma that holds the pte pointing to page
+ * @page:     the cowed page we are replacing by kpage
+ * @kpage:    the modified page we replace page by
+ *
+ * Returns 0 on success, -EFAULT on failure.
+ */
+static int __replace_page(struct vm_area_struct *vma, struct page *page, struct page *kpage)
+{
+        struct mm_struct *mm = vma->vm_mm;
+        pgd_t *pgd;
+        pud_t *pud;
+        pmd_t *pmd;
+        pte_t *ptep;
+        spinlock_t *ptl;
+        unsigned long addr;
+        int err = -EFAULT;
+
+        addr = page_address_in_vma(page, vma);
+        if (addr == -EFAULT)
+                goto out;
+
+        pgd = pgd_offset(mm, addr);
+        if (!pgd_present(*pgd))
+                goto out;
+
+        pud = pud_offset(pgd, addr);
+        if (!pud_present(*pud))
+                goto out;
+
+        pmd = pmd_offset(pud, addr);
+        if (!pmd_present(*pmd))
+                goto out;
+
+        ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
+        if (!ptep)
+                goto out;
+
+        get_page(kpage);
+        page_add_new_anon_rmap(kpage, vma, addr);
+
+        if (!PageAnon(page)) {
+                dec_mm_counter(mm, MM_FILEPAGES);
+                inc_mm_counter(mm, MM_ANONPAGES);
+        }
+
+        flush_cache_page(vma, addr, pte_pfn(*ptep));
+        ptep_clear_flush(vma, addr, ptep);
+        set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
+
+        page_remove_rmap(page);
+        if (!page_mapped(page))
+                try_to_free_swap(page);
+        put_page(page);
+        pte_unmap_unlock(ptep, ptl);
+        err = 0;
+
+out:
+        return err;
+}
+
+/**
+ * is_swbp_insn - check if instruction is breakpoint instruction.
+ * @insn: instruction to be checked.
+ * Default implementation of is_swbp_insn
+ * Returns true if @insn is a breakpoint instruction.
+ */
+bool __weak is_swbp_insn(uprobe_opcode_t *insn)
+{
+        return *insn == UPROBE_SWBP_INSN;
+}
+
+/*
+ * NOTE:
+ * Expect the breakpoint instruction to be the smallest size instruction for
+ * the architecture. If an arch has variable length instruction and the
+ * breakpoint instruction is not of the smallest length instruction
+ * supported by that architecture then we need to modify read_opcode /
+ * write_opcode accordingly. This would never be a problem for archs that
+ * have fixed length instructions.
+ */
+
+/*
+ * write_opcode - write the opcode at a given virtual address.
+ * @auprobe: arch breakpointing information.
+ * @mm: the probed process address space.
+ * @vaddr: the virtual address to store the opcode.
+ * @opcode: opcode to be written at @vaddr.
+ *
+ * Called with mm->mmap_sem held (for read and with a reference to
+ * mm).
+ *
+ * For mm @mm, write the opcode at @vaddr.
+ * Return 0 (success) or a negative errno.
+ */
+static int write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
+                        unsigned long vaddr, uprobe_opcode_t opcode)
+{
+        struct page *old_page, *new_page;
+        struct address_space *mapping;
+        void *vaddr_old, *vaddr_new;
+        struct vm_area_struct *vma;
+        struct uprobe *uprobe;
+        loff_t addr;
+        int ret;
+
+        /* Read the page with vaddr into memory */
+        ret = get_user_pages(NULL, mm, vaddr, 1, 0, 0, &old_page, &vma);
+        if (ret <= 0)
+                return ret;
+
+        ret = -EINVAL;
+
+        /*
+         * We are interested in text pages only. Our pages of interest
+         * should be mapped for read and execute only. We desist from
+         * adding probes in write mapped pages since the breakpoints
+         * might end up in the file copy.
+         */
+        if (!valid_vma(vma, is_swbp_insn(&opcode)))
+                goto put_out;
+
+        uprobe = container_of(auprobe, struct uprobe, arch);
+        mapping = uprobe->inode->i_mapping;
+        if (mapping != vma->vm_file->f_mapping)
+                goto put_out;
+
+        addr = vma_address(vma, uprobe->offset);
+        if (vaddr != (unsigned long)addr)
+                goto put_out;
+
+        ret = -ENOMEM;
+        new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vaddr);
+        if (!new_page)
+                goto put_out;
+
+        __SetPageUptodate(new_page);
+
+        /*
+         * lock page will serialize against do_wp_page()'s
+         * PageAnon() handling
+         */
+        lock_page(old_page);
+        /* copy the page now that we've got it stable */
+        vaddr_old = kmap_atomic(old_page);
+        vaddr_new = kmap_atomic(new_page);
+
+        memcpy(vaddr_new, vaddr_old, PAGE_SIZE);
+
+        /* poke the new insn in, ASSUMES we don't cross page boundary */
+        vaddr &= ~PAGE_MASK;
+        BUG_ON(vaddr + UPROBE_SWBP_INSN_SIZE > PAGE_SIZE);
+        memcpy(vaddr_new + vaddr, &opcode, UPROBE_SWBP_INSN_SIZE);
+
+        kunmap_atomic(vaddr_new);
+        kunmap_atomic(vaddr_old);
+
+        ret = anon_vma_prepare(vma);
+        if (ret)
+                goto unlock_out;
+
+        lock_page(new_page);
+        ret = __replace_page(vma, old_page, new_page);
+        unlock_page(new_page);
+
+unlock_out:
+        unlock_page(old_page);
+        page_cache_release(new_page);
+
+put_out:
+        put_page(old_page);
+
+        return ret;
+}
+
+/**
+ * read_opcode - read the opcode at a given virtual address.
+ * @mm: the probed process address space.
+ * @vaddr: the virtual address to read the opcode.
+ * @opcode: location to store the read opcode.
+ *
+ * Called with mm->mmap_sem held (for read and with a reference to
+ * mm.
+ *
+ * For mm @mm, read the opcode at @vaddr and store it in @opcode.
+ * Return 0 (success) or a negative errno.
+ */
+static int read_opcode(struct mm_struct *mm, unsigned long vaddr, uprobe_opcode_t *opcode)
+{
+        struct page *page;
+        void *vaddr_new;
+        int ret;
+
+        ret = get_user_pages(NULL, mm, vaddr, 1, 0, 0, &page, NULL);
+        if (ret <= 0)
+                return ret;
+
+        lock_page(page);
+        vaddr_new = kmap_atomic(page);
+        vaddr &= ~PAGE_MASK;
+        memcpy(opcode, vaddr_new + vaddr, UPROBE_SWBP_INSN_SIZE);
+        kunmap_atomic(vaddr_new);
+        unlock_page(page);
+
+        put_page(page);
+
+        return 0;
+}
+
+static int is_swbp_at_addr(struct mm_struct *mm, unsigned long vaddr)
+{
+        uprobe_opcode_t opcode;
+        int result;
+
+        result = read_opcode(mm, vaddr, &opcode);
+        if (result)
+                return result;
+
+        if (is_swbp_insn(&opcode))
+                return 1;
+
+        return 0;
+}
+
+/**
+ * set_swbp - store breakpoint at a given address.
+ * @auprobe: arch specific probepoint information.
+ * @mm: the probed process address space.
+ * @vaddr: the virtual address to insert the opcode.
+ *
+ * For mm @mm, store the breakpoint instruction at @vaddr.
+ * Return 0 (success) or a negative errno.
+ */
+int __weak set_swbp(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long vaddr)
+{
+        int result;
+
+        result = is_swbp_at_addr(mm, vaddr);
+        if (result == 1)
+                return -EEXIST;
+
+        if (result)
+                return result;
+
+        return write_opcode(auprobe, mm, vaddr, UPROBE_SWBP_INSN);
+}
+
+/**
+ * set_orig_insn - Restore the original instruction.
+ * @mm: the probed process address space.
+ * @auprobe: arch specific probepoint information.
+ * @vaddr: the virtual address to insert the opcode.
+ * @verify: if true, verify existance of breakpoint instruction.
+ *
+ * For mm @mm, restore the original opcode (opcode) at @vaddr.
+ * Return 0 (success) or a negative errno.
+ */
+int __weak
+set_orig_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long vaddr, bool verify)
+{
+        if (verify) {
+                int result;
+
+                result = is_swbp_at_addr(mm, vaddr);
+                if (!result)
+                        return -EINVAL;
+
+                if (result != 1)
+                        return result;
+        }
+        return write_opcode(auprobe, mm, vaddr, *(uprobe_opcode_t *)auprobe->insn);
+}
+
+static int match_uprobe(struct uprobe *l, struct uprobe *r)
+{
+        if (l->inode < r->inode)
+                return -1;
+
+        if (l->inode > r->inode)
+                return 1;
+
+        if (l->offset < r->offset)
+                return -1;
+
+        if (l->offset > r->offset)
+                return 1;
+
+        return 0;
+}
+
+static struct uprobe *__find_uprobe(struct inode *inode, loff_t offset)
+{
+        struct uprobe u = { .inode = inode, .offset = offset };
+        struct rb_node *n = uprobes_tree.rb_node;
+        struct uprobe *uprobe;
+        int match;
+
+        while (n) {
+                uprobe = rb_entry(n, struct uprobe, rb_node);
+                match = match_uprobe(&u, uprobe);
+                if (!match) {
+                        atomic_inc(&uprobe->ref);
+                        return uprobe;
+                }
+
+                if (match < 0)
+                        n = n->rb_left;
+                else
+                        n = n->rb_right;
+        }
+        return NULL;
+}
+
+/*
+ * Find a uprobe corresponding to a given inode:offset
+ * Acquires uprobes_treelock
+ */
+static struct uprobe *find_uprobe(struct inode *inode, loff_t offset)
+{
+        struct uprobe *uprobe;
+        unsigned long flags;
+
+        spin_lock_irqsave(&uprobes_treelock, flags);
+        uprobe = __find_uprobe(inode, offset);
+        spin_unlock_irqrestore(&uprobes_treelock, flags);
+
+        return uprobe;
+}
+
+static struct uprobe *__insert_uprobe(struct uprobe *uprobe)
+{
+        struct rb_node **p = &uprobes_tree.rb_node;
+        struct rb_node *parent = NULL;
+        struct uprobe *u;
+        int match;
+
+        while (*p) {
+                parent = *p;
+                u = rb_entry(parent, struct uprobe, rb_node);
+                match = match_uprobe(uprobe, u);
+                if (!match) {
+                        atomic_inc(&u->ref);
+                        return u;
+                }
+
+                if (match < 0)
+                        p = &parent->rb_left;
+                else
+                        p = &parent->rb_right;
+
+        }
+
+        u = NULL;
+        rb_link_node(&uprobe->rb_node, parent, p);
+        rb_insert_color(&uprobe->rb_node, &uprobes_tree);
+        /* get access + creation ref */
+        atomic_set(&uprobe->ref, 2);
+
+        return u;
+}
+
+/*
+ * Acquire uprobes_treelock.
+ * Matching uprobe already exists in rbtree;
+ *      increment (access refcount) and return the matching uprobe.
+ *
+ * No matching uprobe; insert the uprobe in rb_tree;
+ *      get a double refcount (access + creation) and return NULL.
+ */
+static struct uprobe *insert_uprobe(struct uprobe *uprobe)
+{
+        unsigned long flags;
+        struct uprobe *u;
+
+        spin_lock_irqsave(&uprobes_treelock, flags);
+        u = __insert_uprobe(uprobe);
+        spin_unlock_irqrestore(&uprobes_treelock, flags);
+
+        /* For now assume that the instruction need not be single-stepped */
+        uprobe->flags |= UPROBE_SKIP_SSTEP;
+
+        return u;
+}
+
+static void put_uprobe(struct uprobe *uprobe)
+{
+        if (atomic_dec_and_test(&uprobe->ref))
+                kfree(uprobe);
+}
+
+static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset)
+{
+        struct uprobe *uprobe, *cur_uprobe;
+
+        uprobe = kzalloc(sizeof(struct uprobe), GFP_KERNEL);
+        if (!uprobe)
+                return NULL;
+
+        uprobe->inode = igrab(inode);
+        uprobe->offset = offset;
+        init_rwsem(&uprobe->consumer_rwsem);
+        INIT_LIST_HEAD(&uprobe->pending_list);
+
+        /* add to uprobes_tree, sorted on inode:offset */
+        cur_uprobe = insert_uprobe(uprobe);
+
+        /* a uprobe exists for this inode:offset combination */
+        if (cur_uprobe) {
+                kfree(uprobe);
+                uprobe = cur_uprobe;
+                iput(inode);
+        } else {
+                atomic_inc(&uprobe_events);
+        }
+
+        return uprobe;
+}
+
+static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
+{
+        struct uprobe_consumer *uc;
+
+        if (!(uprobe->flags & UPROBE_RUN_HANDLER))
+                return;
+
+        down_read(&uprobe->consumer_rwsem);
+        for (uc = uprobe->consumers; uc; uc = uc->next) {
+                if (!uc->filter || uc->filter(uc, current))
+                        uc->handler(uc, regs);
+        }
+        up_read(&uprobe->consumer_rwsem);
+}
+
+/* Returns the previous consumer */
+static struct uprobe_consumer *
+consumer_add(struct uprobe *uprobe, struct uprobe_consumer *uc)
+{
+        down_write(&uprobe->consumer_rwsem);
+        uc->next = uprobe->consumers;
+        uprobe->consumers = uc;
+        up_write(&uprobe->consumer_rwsem);
+
+        return uc->next;
+}
+
+/*
+ * For uprobe @uprobe, delete the consumer @uc.
+ * Return true if the @uc is deleted successfully
+ * or return false.
+ */
+static bool consumer_del(struct uprobe *uprobe, struct uprobe_consumer *uc)
+{
+        struct uprobe_consumer **con;
+        bool ret = false;
+
+        down_write(&uprobe->consumer_rwsem);
+        for (con = &uprobe->consumers; *con; con = &(*con)->next) {
+                if (*con == uc) {
+                        *con = uc->next;
+                        ret = true;
+                        break;
+                }
+        }
+        up_write(&uprobe->consumer_rwsem);
+
+        return ret;
+}
+
+static int
+__copy_insn(struct address_space *mapping, struct vm_area_struct *vma, char *insn,
+                        unsigned long nbytes, unsigned long offset)
+{
+        struct file *filp = vma->vm_file;
+        struct page *page;
+        void *vaddr;
+        unsigned long off1;
+        unsigned long idx;
+
+        if (!filp)
+                return -EINVAL;
+
+        idx = (unsigned long)(offset >> PAGE_CACHE_SHIFT);
+        off1 = offset &= ~PAGE_MASK;
+
+        /*
+         * Ensure that the page that has the original instruction is
+         * populated and in page-cache.
+         */
+        page = read_mapping_page(mapping, idx, filp);
+        if (IS_ERR(page))
+                return PTR_ERR(page);
+
+        vaddr = kmap_atomic(page);
+        memcpy(insn, vaddr + off1, nbytes);
+        kunmap_atomic(vaddr);
+        page_cache_release(page);
+
+        return 0;
+}
+
+static int
+copy_insn(struct uprobe *uprobe, struct vm_area_struct *vma, unsigned long addr)
+{
+        struct address_space *mapping;
+        unsigned long nbytes;
+        int bytes;
+
+        addr &= ~PAGE_MASK;
+        nbytes = PAGE_SIZE - addr;
+        mapping = uprobe->inode->i_mapping;
+
+        /* Instruction at end of binary; copy only available bytes */
+        if (uprobe->offset + MAX_UINSN_BYTES > uprobe->inode->i_size)
+                bytes = uprobe->inode->i_size - uprobe->offset;
+        else
+                bytes = MAX_UINSN_BYTES;
+
+        /* Instruction at the page-boundary; copy bytes in second page */
+        if (nbytes < bytes) {
+                if (__copy_insn(mapping, vma, uprobe->arch.insn + nbytes,
+                                bytes - nbytes, uprobe->offset + nbytes))
+                        return -ENOMEM;
+
+                bytes = nbytes;
+        }
+        return __copy_insn(mapping, vma, uprobe->arch.insn, bytes, uprobe->offset);
+}
+
+/*
+ * How mm->uprobes_state.count gets updated
+ * uprobe_mmap() increments the count if
+ *      - it successfully adds a breakpoint.
+ *      - it cannot add a breakpoint, but sees that there is a underlying
+ *        breakpoint (via a is_swbp_at_addr()).
+ *
+ * uprobe_munmap() decrements the count if
+ *      - it sees a underlying breakpoint, (via is_swbp_at_addr)
+ *        (Subsequent uprobe_unregister wouldnt find the breakpoint
+ *        unless a uprobe_mmap kicks in, since the old vma would be
+ *        dropped just after uprobe_munmap.)
+ *
+ * uprobe_register increments the count if:
+ *      - it successfully adds a breakpoint.
+ *
+ * uprobe_unregister decrements the count if:
+ *      - it sees a underlying breakpoint and removes successfully.
+ *        (via is_swbp_at_addr)
+ *        (Subsequent uprobe_munmap wouldnt find the breakpoint
+ *        since there is no underlying breakpoint after the
+ *        breakpoint removal.)
+ */
+static int
+install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
+                        struct vm_area_struct *vma, loff_t vaddr)
+{
+        unsigned long addr;
+        int ret;
+
+        /*
+         * If probe is being deleted, unregister thread could be done with
+         * the vma-rmap-walk through. Adding a probe now can be fatal since
+         * nobody will be able to cleanup. Also we could be from fork or
+         * mremap path, where the probe might have already been inserted.
+         * Hence behave as if probe already existed.
+         */
+        if (!uprobe->consumers)
+                return -EEXIST;
+
+        addr = (unsigned long)vaddr;
+
+        if (!(uprobe->flags & UPROBE_COPY_INSN)) {
+                ret = copy_insn(uprobe, vma, addr);
+                if (ret)
+                        return ret;
+
+                if (is_swbp_insn((uprobe_opcode_t *)uprobe->arch.insn))
+                        return -EEXIST;
+
+                ret = arch_uprobe_analyze_insn(&uprobe->arch, mm);
+                if (ret)
+                        return ret;
+
+                uprobe->flags |= UPROBE_COPY_INSN;
+        }
+
+        /*
+         * Ideally, should be updating the probe count after the breakpoint
+         * has been successfully inserted. However a thread could hit the
+         * breakpoint we just inserted even before the probe count is
+         * incremented. If this is the first breakpoint placed, breakpoint
+         * notifier might ignore uprobes and pass the trap to the thread.
+         * Hence increment before and decrement on failure.
+         */
+        atomic_inc(&mm->uprobes_state.count);
+        ret = set_swbp(&uprobe->arch, mm, addr);
+        if (ret)
+                atomic_dec(&mm->uprobes_state.count);
+
+        return ret;
+}
+
+static void
+remove_breakpoint(struct uprobe *uprobe, struct mm_struct *mm, loff_t vaddr)
+{
+        if (!set_orig_insn(&uprobe->arch, mm, (unsigned long)vaddr, true))
+                atomic_dec(&mm->uprobes_state.count);
+}
+
+/*
+ * There could be threads that have hit the breakpoint and are entering the
+ * notifier code and trying to acquire the uprobes_treelock. The thread
+ * calling delete_uprobe() that is removing the uprobe from the rb_tree can
+ * race with these threads and might acquire the uprobes_treelock compared
+ * to some of the breakpoint hit threads. In such a case, the breakpoint
+ * hit threads will not find the uprobe. The current unregistering thread
+ * waits till all other threads have hit a breakpoint, to acquire the
+ * uprobes_treelock before the uprobe is removed from the rbtree.
+ */
+static void delete_uprobe(struct uprobe *uprobe)
+{
+        unsigned long flags;
+
+        synchronize_srcu(&uprobes_srcu);
+        spin_lock_irqsave(&uprobes_treelock, flags);
+        rb_erase(&uprobe->rb_node, &uprobes_tree);
+        spin_unlock_irqrestore(&uprobes_treelock, flags);
+        iput(uprobe->inode);
+        put_uprobe(uprobe);
+        atomic_dec(&uprobe_events);
+}
+
+static struct vma_info *
+__find_next_vma_info(struct address_space *mapping, struct list_head *head,
+                        struct vma_info *vi, loff_t offset, bool is_register)
+{
+        struct prio_tree_iter iter;
+        struct vm_area_struct *vma;
+        struct vma_info *tmpvi;
+        unsigned long pgoff;
+        int existing_vma;
+        loff_t vaddr;
+
+        pgoff = offset >> PAGE_SHIFT;
+
+        vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
+                if (!valid_vma(vma, is_register))
+                        continue;
+
+                existing_vma = 0;
+                vaddr = vma_address(vma, offset);
+
+                list_for_each_entry(tmpvi, head, probe_list) {
+                        if (tmpvi->mm == vma->vm_mm && tmpvi->vaddr == vaddr) {
+                                existing_vma = 1;
+                                break;
+                        }
+                }
+
+                /*
+                 * Another vma needs a probe to be installed. However skip
+                 * installing the probe if the vma is about to be unlinked.
+                 */
+                if (!existing_vma && atomic_inc_not_zero(&vma->vm_mm->mm_users)) {
+                        vi->mm = vma->vm_mm;
+                        vi->vaddr = vaddr;
+                        list_add(&vi->probe_list, head);
+
+                        return vi;
+                }
+        }
+
+        return NULL;
+}
+
+/*
+ * Iterate in the rmap prio tree  and find a vma where a probe has not
+ * yet been inserted.
+ */
+static struct vma_info *
+find_next_vma_info(struct address_space *mapping, struct list_head *head,
+                loff_t offset, bool is_register)
+{
+        struct vma_info *vi, *retvi;
+
+        vi = kzalloc(sizeof(struct vma_info), GFP_KERNEL);
+        if (!vi)
+                return ERR_PTR(-ENOMEM);
+
+        mutex_lock(&mapping->i_mmap_mutex);
+        retvi = __find_next_vma_info(mapping, head, vi, offset, is_register);
+        mutex_unlock(&mapping->i_mmap_mutex);
+
+        if (!retvi)
+                kfree(vi);
+
+        return retvi;
+}
+
+static int register_for_each_vma(struct uprobe *uprobe, bool is_register)
+{
+        struct list_head try_list;
+        struct vm_area_struct *vma;
+        struct address_space *mapping;
+        struct vma_info *vi, *tmpvi;
+        struct mm_struct *mm;
+        loff_t vaddr;
+        int ret;
+
+        mapping = uprobe->inode->i_mapping;
+        INIT_LIST_HEAD(&try_list);
+
+        ret = 0;
+
+        for (;;) {
+                vi = find_next_vma_info(mapping, &try_list, uprobe->offset, is_register);
+                if (!vi)
+                        break;
+
+                if (IS_ERR(vi)) {
+                        ret = PTR_ERR(vi);
+                        break;
+                }
+
+                mm = vi->mm;
+                down_read(&mm->mmap_sem);
+                vma = find_vma(mm, (unsigned long)vi->vaddr);
+                if (!vma || !valid_vma(vma, is_register)) {
+                        list_del(&vi->probe_list);
+                        kfree(vi);
+                        up_read(&mm->mmap_sem);
+                        mmput(mm);
+                        continue;
+                }
+                vaddr = vma_address(vma, uprobe->offset);
+                if (vma->vm_file->f_mapping->host != uprobe->inode ||
+                                                vaddr != vi->vaddr) {
+                        list_del(&vi->probe_list);
+                        kfree(vi);
+                        up_read(&mm->mmap_sem);
+                        mmput(mm);
+                        continue;
+                }
+
+                if (is_register)
+                        ret = install_breakpoint(uprobe, mm, vma, vi->vaddr);
+                else
+                        remove_breakpoint(uprobe, mm, vi->vaddr);
+
+                up_read(&mm->mmap_sem);
+                mmput(mm);
+                if (is_register) {
+                        if (ret && ret == -EEXIST)
+                                ret = 0;
+                        if (ret)
+                                break;
+                }
+        }
+
+        list_for_each_entry_safe(vi, tmpvi, &try_list, probe_list) {
+                list_del(&vi->probe_list);
+                kfree(vi);
+        }
+
+        return ret;
+}
+
+static int __uprobe_register(struct uprobe *uprobe)
+{
+        return register_for_each_vma(uprobe, true);
+}
+
+static void __uprobe_unregister(struct uprobe *uprobe)
+{
+        if (!register_for_each_vma(uprobe, false))
+                delete_uprobe(uprobe);
+
+        /* TODO : cant unregister? schedule a worker thread */
+}
+
+/*
+ * uprobe_register - register a probe
+ * @inode: the file in which the probe has to be placed.
+ * @offset: offset from the start of the file.
+ * @uc: information on howto handle the probe..
+ *
+ * Apart from the access refcount, uprobe_register() takes a creation
+ * refcount (thro alloc_uprobe) if and only if this @uprobe is getting
+ * inserted into the rbtree (i.e first consumer for a @inode:@offset
+ * tuple).  Creation refcount stops uprobe_unregister from freeing the
+ * @uprobe even before the register operation is complete. Creation
+ * refcount is released when the last @uc for the @uprobe
+ * unregisters.
+ *
+ * Return errno if it cannot successully install probes
+ * else return 0 (success)
+ */
+int uprobe_register(struct inode *inode, loff_t offset, struct uprobe_consumer *uc)
+{
+        struct uprobe *uprobe;
+        int ret;
+
+        if (!inode || !uc || uc->next)
+                return -EINVAL;
+
+        if (offset > i_size_read(inode))
+                return -EINVAL;
+
+        ret = 0;
+        mutex_lock(uprobes_hash(inode));
+        uprobe = alloc_uprobe(inode, offset);
+
+        if (uprobe && !consumer_add(uprobe, uc)) {
+                ret = __uprobe_register(uprobe);
+                if (ret) {
+                        uprobe->consumers = NULL;
+                        __uprobe_unregister(uprobe);
+                } else {
+                        uprobe->flags |= UPROBE_RUN_HANDLER;
+                }
+        }
+
+        mutex_unlock(uprobes_hash(inode));
+        put_uprobe(uprobe);
+
+        return ret;
+}
+
+/*
+ * uprobe_unregister - unregister a already registered probe.
+ * @inode: the file in which the probe has to be removed.
+ * @offset: offset from the start of the file.
+ * @uc: identify which probe if multiple probes are colocated.
+ */
+void uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consumer *uc)
+{
+        struct uprobe *uprobe;
+
+        if (!inode || !uc)
+                return;
+
+        uprobe = find_uprobe(inode, offset);
+        if (!uprobe)
+                return;
+
+        mutex_lock(uprobes_hash(inode));
+
+        if (consumer_del(uprobe, uc)) {
+                if (!uprobe->consumers) {
+                        __uprobe_unregister(uprobe);
+                        uprobe->flags &= ~UPROBE_RUN_HANDLER;
+                }
+        }
+
+        mutex_unlock(uprobes_hash(inode));
+        if (uprobe)
+                put_uprobe(uprobe);
+}
+
+/*
+ * Of all the nodes that correspond to the given inode, return the node
+ * with the least offset.
+ */
+static struct rb_node *find_least_offset_node(struct inode *inode)
+{
+        struct uprobe u = { .inode = inode, .offset = 0};
+        struct rb_node *n = uprobes_tree.rb_node;
+        struct rb_node *close_node = NULL;
+        struct uprobe *uprobe;
+        int match;
+
+        while (n) {
+                uprobe = rb_entry(n, struct uprobe, rb_node);
+                match = match_uprobe(&u, uprobe);
+
+                if (uprobe->inode == inode)
+                        close_node = n;
+
+                if (!match)
+                        return close_node;
+
+                if (match < 0)
+                        n = n->rb_left;
+                else
+                        n = n->rb_right;
+        }
+
+        return close_node;
+}
+
+/*
+ * For a given inode, build a list of probes that need to be inserted.
+ */
+static void build_probe_list(struct inode *inode, struct list_head *head)
+{
+        struct uprobe *uprobe;
+        unsigned long flags;
+        struct rb_node *n;
+
+        spin_lock_irqsave(&uprobes_treelock, flags);
+
+        n = find_least_offset_node(inode);
+
+        for (; n; n = rb_next(n)) {
+                uprobe = rb_entry(n, struct uprobe, rb_node);
+                if (uprobe->inode != inode)
+                        break;
+
+                list_add(&uprobe->pending_list, head);
+                atomic_inc(&uprobe->ref);
+        }
+
+        spin_unlock_irqrestore(&uprobes_treelock, flags);
+}
+
+/*
+ * Called from mmap_region.
+ * called with mm->mmap_sem acquired.
+ *
+ * Return -ve no if we fail to insert probes and we cannot
+ * bail-out.
+ * Return 0 otherwise. i.e:
+ *
+ *      - successful insertion of probes
+ *      - (or) no possible probes to be inserted.
+ *      - (or) insertion of probes failed but we can bail-out.
+ */
+int uprobe_mmap(struct vm_area_struct *vma)
+{
+        struct list_head tmp_list;
+        struct uprobe *uprobe, *u;
+        struct inode *inode;
+        int ret, count;
+
+        if (!atomic_read(&uprobe_events) || !valid_vma(vma, true))
+                return 0;
+
+        inode = vma->vm_file->f_mapping->host;
+        if (!inode)
+                return 0;
+
+        INIT_LIST_HEAD(&tmp_list);
+        mutex_lock(uprobes_mmap_hash(inode));
+        build_probe_list(inode, &tmp_list);
+
+        ret = 0;
+        count = 0;
+
+        list_for_each_entry_safe(uprobe, u, &tmp_list, pending_list) {
+                loff_t vaddr;
+
+                list_del(&uprobe->pending_list);
+                if (!ret) {
+                        vaddr = vma_address(vma, uprobe->offset);
+
+                        if (vaddr < vma->vm_start || vaddr >= vma->vm_end) {
+                                put_uprobe(uprobe);
+                                continue;
+                        }
+
+                        ret = install_breakpoint(uprobe, vma->vm_mm, vma, vaddr);
+
+                        /* Ignore double add: */
+                        if (ret == -EEXIST) {
+                                ret = 0;
+
+                                if (!is_swbp_at_addr(vma->vm_mm, vaddr))
+                                        continue;
+
+                                /*
+                                 * Unable to insert a breakpoint, but
+                                 * breakpoint lies underneath. Increment the
+                                 * probe count.
+                                 */
+                                atomic_inc(&vma->vm_mm->uprobes_state.count);
+                        }
+
+                        if (!ret)
+                                count++;
+                }
+                put_uprobe(uprobe);
+        }
+
+        mutex_unlock(uprobes_mmap_hash(inode));
+
+        if (ret)
+                atomic_sub(count, &vma->vm_mm->uprobes_state.count);
+
+        return ret;
+}
+
+/*
+ * Called in context of a munmap of a vma.
+ */
+void uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned long end)
+{
+        struct list_head tmp_list;
+        struct uprobe *uprobe, *u;
+        struct inode *inode;
+
+        if (!atomic_read(&uprobe_events) || !valid_vma(vma, false))
+                return;
+
+        if (!atomic_read(&vma->vm_mm->uprobes_state.count))
+                return;
+
+        inode = vma->vm_file->f_mapping->host;
+        if (!inode)
+                return;
+
+        INIT_LIST_HEAD(&tmp_list);
+        mutex_lock(uprobes_mmap_hash(inode));
+        build_probe_list(inode, &tmp_list);
+
+        list_for_each_entry_safe(uprobe, u, &tmp_list, pending_list) {
+                loff_t vaddr;
+
+                list_del(&uprobe->pending_list);
+                vaddr = vma_address(vma, uprobe->offset);
+
+                if (vaddr >= start && vaddr < end) {
+                        /*
+                         * An unregister could have removed the probe before
+                         * unmap. So check before we decrement the count.
+                         */
+                        if (is_swbp_at_addr(vma->vm_mm, vaddr) == 1)
+                                atomic_dec(&vma->vm_mm->uprobes_state.count);
+                }
+                put_uprobe(uprobe);
+        }
+        mutex_unlock(uprobes_mmap_hash(inode));
+}
+
+/* Slot allocation for XOL */
+static int xol_add_vma(struct xol_area *area)
+{
+        struct mm_struct *mm;
+        int ret;
+
+        area->page = alloc_page(GFP_HIGHUSER);
+        if (!area->page)
+                return -ENOMEM;
+
+        ret = -EALREADY;
+        mm = current->mm;
+
+        down_write(&mm->mmap_sem);
+        if (mm->uprobes_state.xol_area)
+                goto fail;
+
+        ret = -ENOMEM;
+
+        /* Try to map as high as possible, this is only a hint. */
+        area->vaddr = get_unmapped_area(NULL, TASK_SIZE - PAGE_SIZE, PAGE_SIZE, 0, 0);
+        if (area->vaddr & ~PAGE_MASK) {
+                ret = area->vaddr;
+                goto fail;
+        }
+
+        ret = install_special_mapping(mm, area->vaddr, PAGE_SIZE,
+                                VM_EXEC|VM_MAYEXEC|VM_DONTCOPY|VM_IO, &area->page);
+        if (ret)
+                goto fail;
+
+        smp_wmb();      /* pairs with get_xol_area() */
+        mm->uprobes_state.xol_area = area;
+        ret = 0;
+
+fail:
+        up_write(&mm->mmap_sem);
+        if (ret)
+                __free_page(area->page);
+
+        return ret;
+}
+
+static struct xol_area *get_xol_area(struct mm_struct *mm)
+{
+        struct xol_area *area;
+
+        area = mm->uprobes_state.xol_area;
+        smp_read_barrier_depends();     /* pairs with wmb in xol_add_vma() */
+
+        return area;
+}
+
+/*
+ * xol_alloc_area - Allocate process's xol_area.
+ * This area will be used for storing instructions for execution out of
+ * line.
+ *
+ * Returns the allocated area or NULL.
+ */
+static struct xol_area *xol_alloc_area(void)
+{
+        struct xol_area *area;
+
+        area = kzalloc(sizeof(*area), GFP_KERNEL);
+        if (unlikely(!area))
+                return NULL;
+
+        area->bitmap = kzalloc(BITS_TO_LONGS(UINSNS_PER_PAGE) * sizeof(long), GFP_KERNEL);
+
+        if (!area->bitmap)
+                goto fail;
+
+        init_waitqueue_head(&area->wq);
+        if (!xol_add_vma(area))
+                return area;
+
+fail:
+        kfree(area->bitmap);
+        kfree(area);
+
+        return get_xol_area(current->mm);
+}
+
+/*
+ * uprobe_clear_state - Free the area allocated for slots.
+ */
+void uprobe_clear_state(struct mm_struct *mm)
+{
+        struct xol_area *area = mm->uprobes_state.xol_area;
+
+        if (!area)
+                return;
+
+        put_page(area->page);
+        kfree(area->bitmap);
+        kfree(area);
+}
+
+/*
+ * uprobe_reset_state - Free the area allocated for slots.
+ */
+void uprobe_reset_state(struct mm_struct *mm)
+{
+        mm->uprobes_state.xol_area = NULL;
+        atomic_set(&mm->uprobes_state.count, 0);
+}
+
+/*
+ *  - search for a free slot.
+ */
+static unsigned long xol_take_insn_slot(struct xol_area *area)
+{
+        unsigned long slot_addr;
+        int slot_nr;
+
+        do {
+                slot_nr = find_first_zero_bit(area->bitmap, UINSNS_PER_PAGE);
+                if (slot_nr < UINSNS_PER_PAGE) {
+                        if (!test_and_set_bit(slot_nr, area->bitmap))
+                                break;
+
+                        slot_nr = UINSNS_PER_PAGE;
+                        continue;
+                }
+                wait_event(area->wq, (atomic_read(&area->slot_count) < UINSNS_PER_PAGE));
+        } while (slot_nr >= UINSNS_PER_PAGE);
+
+        slot_addr = area->vaddr + (slot_nr * UPROBE_XOL_SLOT_BYTES);
+        atomic_inc(&area->slot_count);
+
+        return slot_addr;
+}
+
+/*
+ * xol_get_insn_slot - If was not allocated a slot, then
+ * allocate a slot.
+ * Returns the allocated slot address or 0.
+ */
+static unsigned long xol_get_insn_slot(struct uprobe *uprobe, unsigned long slot_addr)
+{
+        struct xol_area *area;
+        unsigned long offset;
+        void *vaddr;
+
+        area = get_xol_area(current->mm);
+        if (!area) {
+                area = xol_alloc_area();
+                if (!area)
+                        return 0;
+        }
+        current->utask->xol_vaddr = xol_take_insn_slot(area);
+
+        /*
+         * Initialize the slot if xol_vaddr points to valid
+         * instruction slot.
+         */
+        if (unlikely(!current->utask->xol_vaddr))
+                return 0;
+
+        current->utask->vaddr = slot_addr;
+        offset = current->utask->xol_vaddr & ~PAGE_MASK;
+        vaddr = kmap_atomic(area->page);
+        memcpy(vaddr + offset, uprobe->arch.insn, MAX_UINSN_BYTES);
+        kunmap_atomic(vaddr);
+
+        return current->utask->xol_vaddr;
+}
+
+/*
+ * xol_free_insn_slot - If slot was earlier allocated by
+ * @xol_get_insn_slot(), make the slot available for
+ * subsequent requests.
+ */
+static void xol_free_insn_slot(struct task_struct *tsk)
+{
+        struct xol_area *area;
+        unsigned long vma_end;
+        unsigned long slot_addr;
+
+        if (!tsk->mm || !tsk->mm->uprobes_state.xol_area || !tsk->utask)
+                return;
+
+        slot_addr = tsk->utask->xol_vaddr;
+
+        if (unlikely(!slot_addr || IS_ERR_VALUE(slot_addr)))
+                return;
+
+        area = tsk->mm->uprobes_state.xol_area;
+        vma_end = area->vaddr + PAGE_SIZE;
+        if (area->vaddr <= slot_addr && slot_addr < vma_end) {
+                unsigned long offset;
+                int slot_nr;
+
+                offset = slot_addr - area->vaddr;
+                slot_nr = offset / UPROBE_XOL_SLOT_BYTES;
+                if (slot_nr >= UINSNS_PER_PAGE)
+                        return;
+
+                clear_bit(slot_nr, area->bitmap);
+                atomic_dec(&area->slot_count);
+                if (waitqueue_active(&area->wq))
+                        wake_up(&area->wq);
+
+                tsk->utask->xol_vaddr = 0;
+        }
+}
+
+/**
+ * uprobe_get_swbp_addr - compute address of swbp given post-swbp regs
+ * @regs: Reflects the saved state of the task after it has hit a breakpoint
+ * instruction.
+ * Return the address of the breakpoint instruction.
+ */
+unsigned long __weak uprobe_get_swbp_addr(struct pt_regs *regs)
+{
+        return instruction_pointer(regs) - UPROBE_SWBP_INSN_SIZE;
+}
+
+/*
+ * Called with no locks held.
+ * Called in context of a exiting or a exec-ing thread.
+ */
+void uprobe_free_utask(struct task_struct *t)
+{
+        struct uprobe_task *utask = t->utask;
+
+        if (t->uprobe_srcu_id != -1)
+                srcu_read_unlock_raw(&uprobes_srcu, t->uprobe_srcu_id);
+
+        if (!utask)
+                return;
+
+        if (utask->active_uprobe)
+                put_uprobe(utask->active_uprobe);
+
+        xol_free_insn_slot(t);
+        kfree(utask);
+        t->utask = NULL;
+}
+
+/*
+ * Called in context of a new clone/fork from copy_process.
+ */
+void uprobe_copy_process(struct task_struct *t)
+{
+        t->utask = NULL;
+        t->uprobe_srcu_id = -1;
+}
+
+/*
+ * Allocate a uprobe_task object for the task.
+ * Called when the thread hits a breakpoint for the first time.
+ *
+ * Returns:
+ * - pointer to new uprobe_task on success
+ * - NULL otherwise
+ */
+static struct uprobe_task *add_utask(void)
+{
+        struct uprobe_task *utask;
+
+        utask = kzalloc(sizeof *utask, GFP_KERNEL);
+        if (unlikely(!utask))
+                return NULL;
+
+        utask->active_uprobe = NULL;
+        current->utask = utask;
+        return utask;
+}
+
+/* Prepare to single-step probed instruction out of line. */
+static int
+pre_ssout(struct uprobe *uprobe, struct pt_regs *regs, unsigned long vaddr)
+{
+        if (xol_get_insn_slot(uprobe, vaddr) && !arch_uprobe_pre_xol(&uprobe->arch, regs))
+                return 0;
+
+        return -EFAULT;
+}
+
+/*
+ * If we are singlestepping, then ensure this thread is not connected to
+ * non-fatal signals until completion of singlestep.  When xol insn itself
+ * triggers the signal,  restart the original insn even if the task is
+ * already SIGKILL'ed (since coredump should report the correct ip).  This
+ * is even more important if the task has a handler for SIGSEGV/etc, The
+ * _same_ instruction should be repeated again after return from the signal
+ * handler, and SSTEP can never finish in this case.
+ */
+bool uprobe_deny_signal(void)
+{
+        struct task_struct *t = current;
+        struct uprobe_task *utask = t->utask;
+
+        if (likely(!utask || !utask->active_uprobe))
+                return false;
+
+        WARN_ON_ONCE(utask->state != UTASK_SSTEP);
+
+        if (signal_pending(t)) {
+                spin_lock_irq(&t->sighand->siglock);
+                clear_tsk_thread_flag(t, TIF_SIGPENDING);
+                spin_unlock_irq(&t->sighand->siglock);
+
+                if (__fatal_signal_pending(t) || arch_uprobe_xol_was_trapped(t)) {
+                        utask->state = UTASK_SSTEP_TRAPPED;
+                        set_tsk_thread_flag(t, TIF_UPROBE);
+                        set_tsk_thread_flag(t, TIF_NOTIFY_RESUME);
+                }
+        }
+
+        return true;
+}
+
+/*
+ * Avoid singlestepping the original instruction if the original instruction
+ * is a NOP or can be emulated.
+ */
+static bool can_skip_sstep(struct uprobe *uprobe, struct pt_regs *regs)
+{
+        if (arch_uprobe_skip_sstep(&uprobe->arch, regs))
+                return true;
+
+        uprobe->flags &= ~UPROBE_SKIP_SSTEP;
+        return false;
+}
+
+/*
+ * Run handler and ask thread to singlestep.
+ * Ensure all non-fatal signals cannot interrupt thread while it singlesteps.
+ */
+static void handle_swbp(struct pt_regs *regs)
+{
+        struct vm_area_struct *vma;
+        struct uprobe_task *utask;
+        struct uprobe *uprobe;
+        struct mm_struct *mm;
+        unsigned long bp_vaddr;
+
+        uprobe = NULL;
+        bp_vaddr = uprobe_get_swbp_addr(regs);
+        mm = current->mm;
+        down_read(&mm->mmap_sem);
+        vma = find_vma(mm, bp_vaddr);
+
+        if (vma && vma->vm_start <= bp_vaddr && valid_vma(vma, false)) {
+                struct inode *inode;
+                loff_t offset;
+
+                inode = vma->vm_file->f_mapping->host;
+                offset = bp_vaddr - vma->vm_start;
+                offset += (vma->vm_pgoff << PAGE_SHIFT);
+                uprobe = find_uprobe(inode, offset);
+        }
+
+        srcu_read_unlock_raw(&uprobes_srcu, current->uprobe_srcu_id);
+        current->uprobe_srcu_id = -1;
+        up_read(&mm->mmap_sem);
+
+        if (!uprobe) {
+                /* No matching uprobe; signal SIGTRAP. */
+                send_sig(SIGTRAP, current, 0);
+                return;
+        }
+
+        utask = current->utask;
+        if (!utask) {
+                utask = add_utask();
+                /* Cannot allocate; re-execute the instruction. */
+                if (!utask)
+                        goto cleanup_ret;
+        }
+        utask->active_uprobe = uprobe;
+        handler_chain(uprobe, regs);
+        if (uprobe->flags & UPROBE_SKIP_SSTEP && can_skip_sstep(uprobe, regs))
+                goto cleanup_ret;
+
+        utask->state = UTASK_SSTEP;
+        if (!pre_ssout(uprobe, regs, bp_vaddr)) {
+                user_enable_single_step(current);
+                return;
+        }
+
+cleanup_ret:
+        if (utask) {
+                utask->active_uprobe = NULL;
+                utask->state = UTASK_RUNNING;
+        }
+        if (uprobe) {
+                if (!(uprobe->flags & UPROBE_SKIP_SSTEP))
+
+                        /*
+                         * cannot singlestep; cannot skip instruction;
+                         * re-execute the instruction.
+                         */
+                        instruction_pointer_set(regs, bp_vaddr);
+
+                put_uprobe(uprobe);
+        }
+}
+
+/*
+ * Perform required fix-ups and disable singlestep.
+ * Allow pending signals to take effect.
+ */
+static void handle_singlestep(struct uprobe_task *utask, struct pt_regs *regs)
+{
+        struct uprobe *uprobe;
+
+        uprobe = utask->active_uprobe;
+        if (utask->state == UTASK_SSTEP_ACK)
+                arch_uprobe_post_xol(&uprobe->arch, regs);
+        else if (utask->state == UTASK_SSTEP_TRAPPED)
+                arch_uprobe_abort_xol(&uprobe->arch, regs);
+        else
+                WARN_ON_ONCE(1);
+
+        put_uprobe(uprobe);
+        utask->active_uprobe = NULL;
+        utask->state = UTASK_RUNNING;
+        user_disable_single_step(current);
+        xol_free_insn_slot(current);
+
+        spin_lock_irq(&current->sighand->siglock);
+        recalc_sigpending(); /* see uprobe_deny_signal() */
+        spin_unlock_irq(&current->sighand->siglock);
+}
+
+/*
+ * On breakpoint hit, breakpoint notifier sets the TIF_UPROBE flag.  (and on
+ * subsequent probe hits on the thread sets the state to UTASK_BP_HIT) and
+ * allows the thread to return from interrupt.
+ *
+ * On singlestep exception, singlestep notifier sets the TIF_UPROBE flag and
+ * also sets the state to UTASK_SSTEP_ACK and allows the thread to return from
+ * interrupt.
+ *
+ * While returning to userspace, thread notices the TIF_UPROBE flag and calls
+ * uprobe_notify_resume().
+ */
+void uprobe_notify_resume(struct pt_regs *regs)
+{
+        struct uprobe_task *utask;
+
+        utask = current->utask;
+        if (!utask || utask->state == UTASK_BP_HIT)
+                handle_swbp(regs);
+        else
+                handle_singlestep(utask, regs);
+}
+
+/*
+ * uprobe_pre_sstep_notifier gets called from interrupt context as part of
+ * notifier mechanism. Set TIF_UPROBE flag and indicate breakpoint hit.
+ */
+int uprobe_pre_sstep_notifier(struct pt_regs *regs)
+{
+        struct uprobe_task *utask;
+
+        if (!current->mm || !atomic_read(&current->mm->uprobes_state.count))
+                /* task is currently not uprobed */
+                return 0;
+
+        utask = current->utask;
+        if (utask)
+                utask->state = UTASK_BP_HIT;
+
+        set_thread_flag(TIF_UPROBE);
+        current->uprobe_srcu_id = srcu_read_lock_raw(&uprobes_srcu);
+
+        return 1;
+}
+
+/*
+ * uprobe_post_sstep_notifier gets called in interrupt context as part of notifier
+ * mechanism. Set TIF_UPROBE flag and indicate completion of singlestep.
+ */
+int uprobe_post_sstep_notifier(struct pt_regs *regs)
+{
+        struct uprobe_task *utask = current->utask;
+
+        if (!current->mm || !utask || !utask->active_uprobe)
+                /* task is currently not uprobed */
+                return 0;
+
+        utask->state = UTASK_SSTEP_ACK;
+        set_thread_flag(TIF_UPROBE);
+        return 1;
+}
+
+static struct notifier_block uprobe_exception_nb = {
+        .notifier_call          = arch_uprobe_exception_notify,
+        .priority               = INT_MAX-1,    /* notified after kprobes, kgdb */
+};
+
+static int __init init_uprobes(void)
+{
+        int i;
+
+        for (i = 0; i < UPROBES_HASH_SZ; i++) {
+                mutex_init(&uprobes_mutex[i]);
+                mutex_init(&uprobes_mmap_mutex[i]);
+        }
+        init_srcu_struct(&uprobes_srcu);
+
+        return register_die_notifier(&uprobe_exception_nb);
+}
+module_init(init_uprobes);
+
+static void __exit exit_uprobes(void)
+{
+}
+module_exit(exit_uprobes);