uprobes: Introduce find_active_uprobe() helper

No functional changes. Move the "find uprobe" code from
handle_swbp() to the new helper, find_active_uprobe().

Note: with or without this change, the find-active-uprobe logic
is not exactly right. We can race with another thread which
unmaps the memory with the valid uprobe before we take
mm->mmap_sem. We can't find this uprobe simply because
find_vma() fails. In this case we wrongly assume that this trap
was not caused by uprobe and send the erroneous SIGTRAP. See the
next changes.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anton Arapov <anton@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20120529192857.GC8057@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 28 insertions, 19 deletions

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index a0dbc87a2ec6..eaf4d55fd424 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1489,38 +1489,47 @@ static bool can_skip_sstep(struct uprobe *uprobe, struct pt_regs *regs)
         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)
+static struct uprobe *find_active_uprobe(unsigned long bp_vaddr)
 {
+        struct mm_struct *mm = current->mm;
+        struct uprobe *uprobe = NULL;
         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;
+        if (vma && vma->vm_start <= bp_vaddr) {
+                if (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);
+                        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);
 
+        return uprobe;
+}
+
+/*
+ * 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 uprobe_task *utask;
+        struct uprobe *uprobe;
+        unsigned long bp_vaddr;
+
+        bp_vaddr = uprobe_get_swbp_addr(regs);
+        uprobe = find_active_uprobe(bp_vaddr);
+
         if (!uprobe) {
                 /* No matching uprobe; signal SIGTRAP. */
                 send_sig(SIGTRAP, current, 0);