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uprobes: Introduce MMF_HAS_UPROBES

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Add the new MMF_HAS_UPROBES flag. It is set by install_breakpoint()
and it is copied by dup_mmap(), uprobe_pre_sstep_notifier() checks
it to avoid the slow path if the task was never probed. Perhaps it
makes sense to check it in valid_vma(is_register => false) as well.

This needs the new dup_mmap()->uprobe_dup_mmap() hook. We can't use
uprobe_reset_state() or put MMF_HAS_UPROBES into MMF_INIT_MASK, we
need oldmm->mmap_sem to avoid the race with uprobe_register() or
mmap() from another thread.

Currently we never clear this bit, it can be false-positive after
uprobe_unregister() or uprobe_munmap() or if dup_mmap() hits the
probed VM_DONTCOPY vma. But this is fine correctness-wise and has
no effect unless the task hits the non-uprobe breakpoint.

Signed-off-by: Oleg Nesterov <[email protected]>
Acked-by: Srikar Dronamraju <[email protected]>
This commit is contained in:
Oleg Nesterov 2012-08-08 17:11:42 +02:00
commit f8ac4ec9c0
4 changed files with 29 additions and 1 deletions
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22
kernel/events/uprobes.c
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@ -647,6 +647,7 @@ static int
install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
struct vm_area_struct *vma, unsigned long vaddr)
{
bool first_uprobe;
int ret;
/*
@ -678,7 +679,17 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
uprobe->flags |= UPROBE_COPY_INSN;
}
/*
* set MMF_HAS_UPROBES in advance for uprobe_pre_sstep_notifier(),
* the task can hit this breakpoint right after __replace_page().
*/
first_uprobe = !test_bit(MMF_HAS_UPROBES, &mm->flags);
if (first_uprobe)
set_bit(MMF_HAS_UPROBES, &mm->flags);
ret = set_swbp(&uprobe->arch, mm, vaddr);
if (ret && first_uprobe)
clear_bit(MMF_HAS_UPROBES, &mm->flags);
return ret;
}
@ -1032,6 +1043,9 @@ void uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned lon
if (!atomic_read(&vma->vm_mm->mm_users)) /* called by mmput() ? */
return;
if (!test_bit(MMF_HAS_UPROBES, &vma->vm_mm->flags))
return;
/* TODO: unmapping uprobe(s) will need more work */
}
@ -1142,6 +1156,12 @@ void uprobe_reset_state(struct mm_struct *mm)
mm->uprobes_state.xol_area = NULL;
}
void uprobe_dup_mmap(struct mm_struct *oldmm, struct mm_struct *newmm)
{
if (test_bit(MMF_HAS_UPROBES, &oldmm->flags))
set_bit(MMF_HAS_UPROBES, &newmm->flags);
}
/*
* - search for a free slot.
*/
@ -1507,7 +1527,7 @@ int uprobe_pre_sstep_notifier(struct pt_regs *regs)
{
struct uprobe_task *utask;
if (!current->mm)
if (!current->mm || !test_bit(MMF_HAS_UPROBES, &current->mm->flags))
return 0;
utask = current->utask;