linux-kernel - [PATCH 2/5] uprobes: suppress uprobe

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Message-ID: <20120708203003.GA18226@redhat.com>
Date:	Sun, 8 Jul 2012 22:30:03 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anton Arapov <anton@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/5] 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@...hat.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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