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>
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@ -819,7 +819,6 @@ static int exec_mmap(struct mm_struct *mm)
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/* Notify parent that we're no longer interested in the old VM */
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tsk = current;
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old_mm = current->mm;
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sync_mm_rss(old_mm);
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mm_release(tsk, old_mm);
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if (old_mm) {
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@ -423,6 +423,7 @@ void daemonize(const char *name, ...)
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* user space pages. We don't need them, and if we didn't close them
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* they would be locked into memory.
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*/
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mm_release(current, current->mm);
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exit_mm(current);
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/*
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* We don't want to get frozen, in case system-wide hibernation
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@ -640,7 +641,6 @@ static void exit_mm(struct task_struct * tsk)
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struct mm_struct *mm = tsk->mm;
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struct core_state *core_state;
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mm_release(tsk, mm);
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if (!mm)
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return;
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/*
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@ -960,9 +960,13 @@ void do_exit(long code)
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preempt_count());
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acct_update_integrals(tsk);
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/* sync mm's RSS info before statistics gathering */
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if (tsk->mm)
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sync_mm_rss(tsk->mm);
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/* Set exit_code before complete_vfork_done() in mm_release() */
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tsk->exit_code = code;
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/* Release mm and sync mm's RSS info before statistics gathering */
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mm_release(tsk, tsk->mm);
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group_dead = atomic_dec_and_test(&tsk->signal->live);
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if (group_dead) {
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hrtimer_cancel(&tsk->signal->real_timer);
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@ -975,7 +979,6 @@ void do_exit(long code)
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tty_audit_exit();
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audit_free(tsk);
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tsk->exit_code = code;
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taskstats_exit(tsk, group_dead);
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exit_mm(tsk);
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@ -619,6 +619,14 @@ void mmput(struct mm_struct *mm)
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module_put(mm->binfmt->module);
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mmdrop(mm);
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}
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/*
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* Final rss-counter synchronization. After this point there must be
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* no pagefaults into this mm from the current context. Otherwise
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* mm->rss_stat will be inconsistent.
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*/
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if (mm)
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sync_mm_rss(mm);
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}
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EXPORT_SYMBOL_GPL(mmput);
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