From: Konstantin Khlebnikov <[email protected]> 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. [[email protected]: tweak comment] Signed-off-by: Konstantin Khlebnikov <[email protected]> Reported-by: Markus Trippelsdorf <[email protected]> Cc: Hugh Dickins <[email protected]> Cc: KAMEZAWA Hiroyuki <[email protected]> Cc: Oleg Nesterov <[email protected]> Cc: <[email protected]> [3.4.x] Signed-off-by: Andrew Morton <[email protected]> --- fs/exec.c | 1 - kernel/exit.c | 13 ++++++++----- kernel/fork.c | 8 ++++++++ 3 files changed, 16 insertions(+), 6 deletions(-) diff -puN fs/exec.c~mm-correctly-synchronize-rss-counters-at-exit-exec fs/exec.c --- a/fs/exec.c~mm-correctly-synchronize-rss-counters-at-exit-exec +++ a/fs/exec.c @@ -819,7 +819,6 @@ static int exec_mmap(struct mm_struct *m /* 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) { diff -puN kernel/exit.c~mm-correctly-synchronize-rss-counters-at-exit-exec kernel/exit.c --- a/kernel/exit.c~mm-correctly-synchronize-rss-counters-at-exit-exec +++ a/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 * 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); diff -puN kernel/fork.c~mm-correctly-synchronize-rss-counters-at-exit-exec kernel/fork.c --- a/kernel/fork.c~mm-correctly-synchronize-rss-counters-at-exit-exec +++ a/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); _ -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
