From 40af1bbdca47e5c8a2044039bb78ca8fd8b20f94 Mon Sep 17 00:00:00 2001 From: Konstantin Khlebnikov Date: Thu, 7 Jun 2012 14:21:14 -0700 Subject: 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 Reported-by: Markus Trippelsdorf Cc: Hugh Dickins Cc: KAMEZAWA Hiroyuki Cc: Oleg Nesterov Cc: [3.4.x] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/fork.c | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'kernel/fork.c') diff --git a/kernel/fork.c b/kernel/fork.c index ab5211b9e622..0560781c6904 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); -- cgit v1.2.3