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authorKonstantin Khlebnikov <khlebnikov@openvz.org>2012-06-07 14:21:14 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-06-07 14:43:55 -0700
commit40af1bbdca47e5c8a2044039bb78ca8fd8b20f94 (patch)
tree70b5a21579f8b0137c09e54d523246d84be93430 /kernel/fork.c
parent39caa0916ef27cf1da5026eb708a2b8413156f75 (diff)
mm: correctly synchronize rss-counters at exit/exec
mm->rss_stat counters have per-task delta: task->rss_stat. Before changing task->mm pointer the kernel must flush this delta with sync_mm_rss(). do_exit() already calls sync_mm_rss() to flush the rss-counters before committing the rss statistics into task->signal->maxrss, taskstats, audit and other stuff. Unfortunately the kernel does this before calling mm_release(), which can call put_user() for processing task->clear_child_tid. So at this point we can trigger page-faults and task->rss_stat becomes non-zero again. As a result mm->rss_stat becomes inconsistent and check_mm() will print something like this: | BUG: Bad rss-counter state mm:ffff88020813c380 idx:1 val:-1 | BUG: Bad rss-counter state mm:ffff88020813c380 idx:2 val:1 This patch moves sync_mm_rss() into mm_release(), and moves mm_release() out of do_exit() and calls it earlier. After mm_release() there should be no pagefaults. [akpm@linux-foundation.org: tweak comment] Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org> Reported-by: Markus Trippelsdorf <markus@trippelsdorf.de> Cc: Hugh Dickins <hughd@google.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: <stable@vger.kernel.org> [3.4.x] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/fork.c')
-rw-r--r--kernel/fork.c8
1 files changed, 8 insertions, 0 deletions
diff --git a/kernel/fork.c b/kernel/fork.c
index ab5211b9e62..0560781c690 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -619,6 +619,14 @@ void mmput(struct mm_struct *mm)
module_put(mm->binfmt->module);
mmdrop(mm);
}
+
+ /*
+ * Final rss-counter synchronization. After this point there must be
+ * no pagefaults into this mm from the current context. Otherwise
+ * mm->rss_stat will be inconsistent.
+ */
+ if (mm)
+ sync_mm_rss(mm);
}
EXPORT_SYMBOL_GPL(mmput);