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uprobes: Teach find_active_uprobe() to provide the "is_swbp" info

Browse source 
A separate patch to simplify the review, and for the
documentation.

The patch adds another "int *is_swbp" argument to
find_active_uprobe(), so far its only caller doesn't use this
info.

With this patch find_active_uprobe() additionally does:

	- if find_vma() + ->vm_start check fails, *is_swbp = -EFAULT

	- otherwise, if valid_vma() + find_uprobe() fails, it holds
	  the result of is_swbp_at_addr(), can be negative too. The
	  latter is only possible if we raced with another thread
	  which did munmap/etc after we hit this bp.

IOW. If find_active_uprobe(&is_swbp) returns NULL, the caller
can look at is_swbp to figure out whether the current insn is bp
or not, or detect the race with another thread if it is
negative.

Note: I think that performance-wise this change is fine. This
adds is_swbp_at_addr(), but only if we raced with
uprobe_unregister() or if we hit the "normal" int3 but this mm
has uprobes as well. And even in this case the slow
read_opcode() path is very unlikely, this insn recently
triggered do_int3(), __copy_from_user_inatomic() shouldn't fail
in the likely case.

Signed-off-by: Oleg Nesterov <[email protected]>
Acked-by: Srikar Dronamraju <[email protected]>
Cc: Ananth N Mavinakayanahalli <[email protected]>
Cc: Anton Arapov <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Oleg Nesterov 2012-05-29 21:29:14 +02:00 • committed by Ingo Molnar
commit d790d34653
1 changed files with 8 additions and 3 deletions
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11
kernel/events/uprobes.c
View file

@ -1489,7 +1489,7 @@ static bool can_skip_sstep(struct uprobe *uprobe, struct pt_regs *regs)
return false;
}
static struct uprobe *find_active_uprobe(unsigned long bp_vaddr)
static struct uprobe *find_active_uprobe(unsigned long bp_vaddr, int *is_swbp)
{
struct mm_struct *mm = current->mm;
struct uprobe *uprobe = NULL;
@ -1497,7 +1497,6 @@ static struct uprobe *find_active_uprobe(unsigned long bp_vaddr)
down_read(&mm->mmap_sem);
vma = find_vma(mm, bp_vaddr);
if (vma && vma->vm_start <= bp_vaddr) {
if (valid_vma(vma, false)) {
struct inode *inode;
@ -1508,6 +1507,11 @@ static struct uprobe *find_active_uprobe(unsigned long bp_vaddr)
offset += (vma->vm_pgoff << PAGE_SHIFT);
uprobe = find_uprobe(inode, offset);
}
if (!uprobe)
*is_swbp = is_swbp_at_addr(mm, bp_vaddr);
} else {
*is_swbp = -EFAULT;
}
srcu_read_unlock_raw(&uprobes_srcu, current->uprobe_srcu_id);
@ -1526,9 +1530,10 @@ static void handle_swbp(struct pt_regs *regs)
struct uprobe_task *utask;
struct uprobe *uprobe;
unsigned long bp_vaddr;
int is_swbp;
bp_vaddr = uprobe_get_swbp_addr(regs);
uprobe = find_active_uprobe(bp_vaddr);
uprobe = find_active_uprobe(bp_vaddr, &is_swbp);
if (!uprobe) {
/* No matching uprobe; signal SIGTRAP. */