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/exit.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) (limited to 'kernel/exit.c') diff --git a/kernel/exit.c b/kernel/exit.c index 34867cc5b42a..804fb6bb8161 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -423,6 +423,7 @@ void daemonize(const char *name, ...) * user space pages. We don't need them, and if we didn't close them * they would be locked into memory. */ + mm_release(current, current->mm); exit_mm(current); /* * We don't want to get frozen, in case system-wide hibernation @@ -640,7 +641,6 @@ static void exit_mm(struct task_struct * tsk) struct mm_struct *mm = tsk->mm; struct core_state *core_state; - mm_release(tsk, mm); if (!mm) return; /* @@ -960,9 +960,13 @@ void do_exit(long code) preempt_count()); acct_update_integrals(tsk); - /* sync mm's RSS info before statistics gathering */ - if (tsk->mm) - sync_mm_rss(tsk->mm); + + /* Set exit_code before complete_vfork_done() in mm_release() */ + tsk->exit_code = code; + + /* Release mm and sync mm's RSS info before statistics gathering */ + mm_release(tsk, tsk->mm); + group_dead = atomic_dec_and_test(&tsk->signal->live); if (group_dead) { hrtimer_cancel(&tsk->signal->real_timer); @@ -975,7 +979,6 @@ void do_exit(long code) tty_audit_exit(); audit_free(tsk); - tsk->exit_code = code; taskstats_exit(tsk, group_dead); exit_mm(tsk); -- cgit v1.2.3