From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx175.postini.com [74.125.245.175]) by kanga.kvack.org (Postfix) with SMTP id 054836B0083 for ; Wed, 25 Apr 2012 16:01:26 -0400 (EDT) Date: Wed, 25 Apr 2012 13:01:24 -0700 From: Andrew Morton Subject: Re: [PATCH 1/2] mm: set task exit code before complete_vfork_done() Message-Id: <20120425130124.50ba066b.akpm@linux-foundation.org> In-Reply-To: <20120420204129.GA8034@redhat.com> References: <20120409200336.8368.63793.stgit@zurg> <20120412080948.26401.23572.stgit@zurg> <20120412235446.GA4815@redhat.com> <20120420175934.GA31905@redhat.com> <4F91B7AF.8040203@openvz.org> <20120420204129.GA8034@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Oleg Nesterov Cc: Konstantin Khlebnikov , Hugh Dickins , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , Markus Trippelsdorf , KAMEZAWA Hiroyuki On Fri, 20 Apr 2012 22:41:29 +0200 Oleg Nesterov wrote: > >> IOW, what do you think about the trivial patch below? Uncompiled, > >> untested, probably incomplete. acct_update_integrals() looks > >> suspicious too. > > > > what a mess! =) > > Thanks ;) > > But it is much, much simpler than your patches, don't you agree? Here's what we currently have: From: Konstantin Khlebnikov 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 Signed-off-by: Andrew Morton --- 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 @@ -823,7 +823,6 @@ 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; /* @@ -959,9 +959,13 @@ 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); @@ -974,7 +978,6 @@ 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 @@ -782,6 +782,14 @@ void mm_release(struct task_struct *tsk, } tsk->clear_child_tid = NULL; } + + /* + * 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); } /* _ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org