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Subject[tip:perf/core] uprobes: Suppress uprobe_munmap() from mmput()
Commit-ID:  2fd611a991391a6050cbd139201a2e12fc306540
Gitweb: http://git.kernel.org/tip/2fd611a991391a6050cbd139201a2e12fc306540
Author: Oleg Nesterov <oleg@redhat.com>
AuthorDate: Sun, 29 Jul 2012 20:22:31 +0200
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 30 Jul 2012 11:27:21 +0200

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>
Cc: Anton Arapov <anton@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20120729182231.GA20336@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
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 bed2161..9db9cdf 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;


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