2 files changed, 977 insertions, 0 deletions

diff --git a/kernel/Makefile b/kernel/Makefile
index 2d9de86b7e76..8609dd3d875a 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -107,6 +107,7 @@ obj-$(CONFIG_USER_RETURN_NOTIFIER) += user-return-notifier.o
 obj-$(CONFIG_PADATA) += padata.o
 obj-$(CONFIG_CRASH_DUMP) += crash_dump.o
 obj-$(CONFIG_JUMP_LABEL) += jump_label.o
+obj-$(CONFIG_UPROBES) += uprobes.o
 
 $(obj)/configs.o: $(obj)/config_data.h
 
diff --git a/kernel/uprobes.c b/kernel/uprobes.c
new file mode 100644
index 000000000000..72e8bb3b52cd
--- /dev/null
+++ b/kernel/uprobes.c
@@ -0,0 +1,976 @@
+/*
+ * Userspace 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, 2008-2011
+ * Authors:
+ *      Srikar Dronamraju
+ *      Jim Keniston
+ */
+
+#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/uprobes.h>
+
+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 mmap_uprobe 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;
+};
+
+/*
+ * 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);
+
+        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_bkpt_insn - check if instruction is breakpoint instruction.
+ * @insn: instruction to be checked.
+ * Default implementation of is_bkpt_insn
+ * Returns true if @insn is a breakpoint instruction.
+ */
+bool __weak is_bkpt_insn(uprobe_opcode_t *insn)
+{
+        return (*insn == UPROBES_BKPT_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.
+ * @mm: the probed process address space.
+ * @uprobe: the breakpointing information.
+ * @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 mm_struct *mm, struct uprobe *uprobe,
+                        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;
+        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_bkpt_insn(&opcode)))
+                goto put_out;
+
+        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_opcode_sz > PAGE_SIZE);
+        memcpy(vaddr_new + vaddr, &opcode, uprobe_opcode_sz);
+
+        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);     /* we did a get_page in the beginning */
+        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_opcode_sz);
+        kunmap_atomic(vaddr_new);
+        unlock_page(page);
+        put_page(page);         /* we did a get_user_pages in the beginning */
+        return 0;
+}
+
+static int is_bkpt_at_addr(struct mm_struct *mm, unsigned long vaddr)
+{
+        uprobe_opcode_t opcode;
+        int result = read_opcode(mm, vaddr, &opcode);
+
+        if (result)
+                return result;
+
+        if (is_bkpt_insn(&opcode))
+                return 1;
+
+        return 0;
+}
+
+/**
+ * set_bkpt - store breakpoint at a given address.
+ * @mm: the probed process address space.
+ * @uprobe: the probepoint information.
+ * @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_bkpt(struct mm_struct *mm, struct uprobe *uprobe,
+                                                unsigned long vaddr)
+{
+        int result = is_bkpt_at_addr(mm, vaddr);
+
+        if (result == 1)
+                return -EEXIST;
+
+        if (result)
+                return result;
+
+        return write_opcode(mm, uprobe, vaddr, UPROBES_BKPT_INSN);
+}
+
+/**
+ * set_orig_insn - Restore the original instruction.
+ * @mm: the probed process address space.
+ * @uprobe: the 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 mm_struct *mm, struct uprobe *uprobe,
+                                        unsigned long vaddr, bool verify)
+{
+        if (verify) {
+                int result = is_bkpt_at_addr(mm, vaddr);
+
+                if (!result)
+                        return -EINVAL;
+
+                if (result != 1)
+                        return result;
+        }
+        return write_opcode(mm, uprobe, vaddr,
+                                *(uprobe_opcode_t *)uprobe->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;
+        else {
+                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;
+}
+
+/*
+ * Acquires 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);
+        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;
+}
+
+/* Returns the previous consumer */
+static struct uprobe_consumer *add_consumer(struct uprobe *uprobe,
+                                struct uprobe_consumer *consumer)
+{
+        down_write(&uprobe->consumer_rwsem);
+        consumer->next = uprobe->consumers;
+        uprobe->consumers = consumer;
+        up_write(&uprobe->consumer_rwsem);
+        return consumer->next;
+}
+
+/*
+ * For uprobe @uprobe, delete the consumer @consumer.
+ * Return true if the @consumer is deleted successfully
+ * or return false.
+ */
+static bool del_consumer(struct uprobe *uprobe,
+                                struct uprobe_consumer *consumer)
+{
+        struct uprobe_consumer **con;
+        bool ret = false;
+
+        down_write(&uprobe->consumer_rwsem);
+        for (con = &uprobe->consumers; *con; con = &(*con)->next) {
+                if (*con == consumer) {
+                        *con = consumer->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;
+        int bytes;
+        unsigned long nbytes;
+
+        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->insn + nbytes,
+                                bytes - nbytes, uprobe->offset + nbytes))
+                        return -ENOMEM;
+
+                bytes = nbytes;
+        }
+        return __copy_insn(mapping, vma, uprobe->insn, bytes, uprobe->offset);
+}
+
+static int install_breakpoint(struct mm_struct *mm, struct uprobe *uprobe,
+                                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 & UPROBES_COPY_INSN)) {
+                ret = copy_insn(uprobe, vma, addr);
+                if (ret)
+                        return ret;
+
+                if (is_bkpt_insn((uprobe_opcode_t *)uprobe->insn))
+                        return -EEXIST;
+
+                ret = analyze_insn(mm, uprobe);
+                if (ret)
+                        return ret;
+
+                uprobe->flags |= UPROBES_COPY_INSN;
+        }
+        ret = set_bkpt(mm, uprobe, addr);
+
+        return ret;
+}
+
+static void remove_breakpoint(struct mm_struct *mm, struct uprobe *uprobe,
+                                                        loff_t vaddr)
+{
+        set_orig_insn(mm, uprobe, (unsigned long)vaddr, true);
+}
+
+static void delete_uprobe(struct uprobe *uprobe)
+{
+        unsigned long flags;
+
+        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 list_head *head,
+                        loff_t offset, struct address_space *mapping,
+                        struct vma_info *vi, bool is_register)
+{
+        struct prio_tree_iter iter;
+        struct vm_area_struct *vma;
+        struct vma_info *tmpvi;
+        loff_t vaddr;
+        unsigned long pgoff = offset >> PAGE_SHIFT;
+        int existing_vma;
+
+        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 list_head *head,
+                        loff_t offset, struct address_space *mapping,
+                        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(head, offset, mapping, vi, 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 = 0;
+
+        mapping = uprobe->inode->i_mapping;
+        INIT_LIST_HEAD(&try_list);
+        while ((vi = find_next_vma_info(&try_list, uprobe->offset,
+                                        mapping, is_register)) != NULL) {
+                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(mm, uprobe, vma, vi->vaddr);
+                else
+                        remove_breakpoint(mm, uprobe, 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 __register_uprobe(struct uprobe *uprobe)
+{
+        return register_for_each_vma(uprobe, true);
+}
+
+static void __unregister_uprobe(struct uprobe *uprobe)
+{
+        if (!register_for_each_vma(uprobe, false))
+                delete_uprobe(uprobe);
+
+        /* TODO : cant unregister? schedule a worker thread */
+}
+
+/*
+ * register_uprobe - register a probe
+ * @inode: the file in which the probe has to be placed.
+ * @offset: offset from the start of the file.
+ * @consumer: information on howto handle the probe..
+ *
+ * Apart from the access refcount, register_uprobe() 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 unregister_uprobe from freeing the
+ * @uprobe even before the register operation is complete. Creation
+ * refcount is released when the last @consumer for the @uprobe
+ * unregisters.
+ *
+ * Return errno if it cannot successully install probes
+ * else return 0 (success)
+ */
+int register_uprobe(struct inode *inode, loff_t offset,
+                                struct uprobe_consumer *consumer)
+{
+        struct uprobe *uprobe;
+        int ret = -EINVAL;
+
+        if (!inode || !consumer || consumer->next)
+                return ret;
+
+        if (offset > i_size_read(inode))
+                return ret;
+
+        ret = 0;
+        mutex_lock(uprobes_hash(inode));
+        uprobe = alloc_uprobe(inode, offset);
+        if (uprobe && !add_consumer(uprobe, consumer)) {
+                ret = __register_uprobe(uprobe);
+                if (ret) {
+                        uprobe->consumers = NULL;
+                        __unregister_uprobe(uprobe);
+                } else
+                        uprobe->flags |= UPROBES_RUN_HANDLER;
+        }
+
+        mutex_unlock(uprobes_hash(inode));
+        put_uprobe(uprobe);
+
+        return ret;
+}
+
+/*
+ * unregister_uprobe - unregister a already registered probe.
+ * @inode: the file in which the probe has to be removed.
+ * @offset: offset from the start of the file.
+ * @consumer: identify which probe if multiple probes are colocated.
+ */
+void unregister_uprobe(struct inode *inode, loff_t offset,
+                                struct uprobe_consumer *consumer)
+{
+        struct uprobe *uprobe = NULL;
+
+        if (!inode || !consumer)
+                return;
+
+        uprobe = find_uprobe(inode, offset);
+        if (!uprobe)
+                return;
+
+        mutex_lock(uprobes_hash(inode));
+        if (!del_consumer(uprobe, consumer))
+                goto unreg_out;
+
+        if (!uprobe->consumers) {
+                __unregister_uprobe(uprobe);
+                uprobe->flags &= ~UPROBES_RUN_HANDLER;
+        }
+
+unreg_out:
+        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;
+        struct rb_node *n;
+        unsigned long flags;
+
+        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 mmap_uprobe(struct vm_area_struct *vma)
+{
+        struct list_head tmp_list;
+        struct uprobe *uprobe, *u;
+        struct inode *inode;
+        int ret = 0;
+
+        if (!atomic_read(&uprobe_events) || !valid_vma(vma, true))
+                return ret;     /* Bail-out */
+
+        inode = vma->vm_file->f_mapping->host;
+        if (!inode)
+                return ret;
+
+        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);
+                if (!ret) {
+                        vaddr = vma_address(vma, uprobe->offset);
+                        if (vaddr < vma->vm_start || vaddr >= vma->vm_end) {
+                                put_uprobe(uprobe);
+                                continue;
+                        }
+                        ret = install_breakpoint(vma->vm_mm, uprobe, vma,
+                                                                vaddr);
+                        if (ret == -EEXIST)
+                                ret = 0;
+                }
+                put_uprobe(uprobe);
+        }
+
+        mutex_unlock(uprobes_mmap_hash(inode));
+
+        return ret;
+}
+
+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]);
+        }
+        return 0;
+}
+
+static void __exit exit_uprobes(void)
+{
+}
+
+module_init(init_uprobes);
+module_exit(exit_uprobes);