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Subject[PATCH 06/14] uprobes: suppress uprobe_munmap() from mmput()
uprobe_munmap() does get_user_pages() and it is also called from
the final mmput()->exit_mmap() path. This slows down exit/mmput()
for no reason, and I think it is simply dangerous/wrong to try to
fault-in a page into the dying mm. If nothing else, this happens
after the last sync_mm_rss(), afaics handle_mm_fault() can change
the task->rss_stat and make the subsequent check_mm() unhappy.

Change uprobe_munmap() to check mm->mm_users != 0.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar.vnet.ibm.com>
---
kernel/events/uprobes.c | 3 +++
1 files changed, 3 insertions(+), 0 deletions(-)
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index a93b6df..47c4e24 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1082,6 +1082,9 @@ void uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned lon
if (!atomic_read(&uprobe_events) || !valid_vma(vma, false))
return;

+ if (!atomic_read(&vma->vm_mm->mm_users)) /* called by mmput() ? */
+ return;
+
if (!atomic_read(&vma->vm_mm->uprobes_state.count))
return;

--
1.5.5.1


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