* Oleg Nesterov <o...@redhat.com> [2012-08-19 18:40:42]:
> The wrong MMF_HAS_UPROBES doesn't really hurt, just it triggers
> the "slow" and unnecessary handle_swbp() path if the task hits
> the non-uprobe breakpoint.
>
> So this patch changes find_active_uprobe() to check every valid
> vma and clear MMF_HAS_UPROBES if no uprobes were found. This is
> adds the slow O(n) path, but it is only called in unlikely case
> when the task hits the normal breakpoint first time after
> uprobe_unregister().
>
> Note the "not strictly accurate" comment in mmf_recalc_uprobes().
> We can fix this, we only need to teach vma_has_uprobes() to return
> a bit more more info, but I am not sure this worth the trouble.
>
> Signed-off-by: Oleg Nesterov <o...@redhat.com>
> ---
> kernel/events/uprobes.c | 22 ++++++++++++++++++++++
> 1 files changed, 22 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 176de8c..0b7918c 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1397,6 +1397,25 @@ static bool can_skip_sstep(struct uprobe *uprobe,
> struct pt_regs *regs)
> return false;
> }
>
> +static void mmf_recalc_uprobes(struct mm_struct *mm)
> +{
> + struct vm_area_struct *vma;
> +
> + for (vma = mm->mmap; vma; vma = vma->vm_next) {
> + if (!valid_vma(vma, false))
> + continue;
> + /*
> + * This is not strictly accurate, we can race with
> + * uprobe_unregister() and see the already removed
> + * uprobe if delete_uprobe() was not yet called.
> + */
> + if (vma_has_uprobes(vma, vma->vm_start, vma->vm_end))
Should we set the MMF_RECALC_UPROBES here?
Its harmless but my thought was if we indeed saw a uprobe that was
already deleted, then the next time we hit a non uprobe breakpoint in
the same process context, we will not come here because
MMF_RECALC_UPROBES is cleared.
The rest looks fine.
Acked-by: Srikar Dronamraju <sri...@linux.vnet.ibm.com>
> + return;
> + }
> +
> + clear_bit(MMF_HAS_UPROBES, &mm->flags);
> +}
> +
> static struct uprobe *find_active_uprobe(unsigned long bp_vaddr, int
> *is_swbp)
> {
> struct mm_struct *mm = current->mm;
> @@ -1418,6 +1437,9 @@ static struct uprobe *find_active_uprobe(unsigned long
> bp_vaddr, int *is_swbp)
> } else {
> *is_swbp = -EFAULT;
> }
> +
> + if (!uprobe && test_and_clear_bit(MMF_RECALC_UPROBES, &mm->flags))
> + mmf_recalc_uprobes(mm);
> up_read(&mm->mmap_sem);
>
> return uprobe;
> --
> 1.5.5.1
>
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