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Commit 40af1bbd authored by Konstantin Khlebnikov's avatar Konstantin Khlebnikov Committed by Linus Torvalds
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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: default avatarKonstantin Khlebnikov <khlebnikov@openvz.org>
Reported-by: default avatarMarkus 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 39caa091

fs/exec.c

+0 −1
Original line number Diff line number Diff line
@@ -819,7 +819,6 @@ static int exec_mmap(struct mm_struct *mm) 
	/* Notify parent that we're no longer interested in the old VM */

	tsk = current;

	old_mm = current->mm;

	sync_mm_rss(old_mm);

	mm_release(tsk, old_mm);



	if (old_mm) {

kernel/exit.c

+8 −5
Original line number Diff line number Diff line
@@ -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);

kernel/fork.c

+8 −0
Original line number Diff line number Diff line
@@ -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);