uprobes: Teach find_active_uprobe() to clear MMF_HAS_UPROBES (499a4f3e) · Commits · 戴 / test

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 <oleg@redhat.com> Acked-by:

Srikar Dronamraju <srikar@linux.vnet.ibm.com>

kernel/events/uprobes.c

+22 −0

Original line number	Diff line number	Diff line
		@@ -1396,6 +1396,25 @@ 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))
		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;
		@@ -1417,6 +1436,9 @@ 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;

Admin message