mm: correctly synchronize rss-counters at exit/exec (40af1bbd) · Commits · 戴 / test

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>

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);

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