From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752020AbcIGHBb (ORCPT ); Wed, 7 Sep 2016 03:01:31 -0400 Received: from merlin.infradead.org ([205.233.59.134]:44844 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750791AbcIGHBa (ORCPT ); Wed, 7 Sep 2016 03:01:30 -0400 Date: Wed, 7 Sep 2016 09:01:24 +0200 From: Peter Zijlstra To: Stanislaw Gruszka Cc: linux-kernel@vger.kernel.org, Giovanni Gherdovich , Linus Torvalds , Mel Gorman , Mike Galbraith , Paolo Bonzini , Rik van Riel , Thomas Gleixner , Wanpeng Li , Ingo Molnar Subject: Re: [PATCH v3] sched/cputime: Protect some other sum_exec_runtime reads on 32 bit cpus Message-ID: <20160907070124.GP10153@twins.programming.kicks-ass.net> References: <1473166148-8466-1-git-send-email-sgruszka@redhat.com> <20160906190129.GO10153@twins.programming.kicks-ass.net> <20160907063826.GA16999@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160907063826.GA16999@redhat.com> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 07, 2016 at 08:38:27AM +0200, Stanislaw Gruszka wrote: > On Tue, Sep 06, 2016 at 09:01:29PM +0200, Peter Zijlstra wrote: > > On Tue, Sep 06, 2016 at 02:49:08PM +0200, Stanislaw Gruszka wrote: > > > diff --git a/kernel/exit.c b/kernel/exit.c > > > index 2f974ae..a46f96f 100644 > > > --- a/kernel/exit.c > > > +++ b/kernel/exit.c > > > @@ -134,7 +134,7 @@ static void __exit_signal(struct task_struct *tsk) > > > sig->inblock += task_io_get_inblock(tsk); > > > sig->oublock += task_io_get_oublock(tsk); > > > task_io_accounting_add(&sig->ioac, &tsk->ioac); > > > - sig->sum_sched_runtime += tsk->se.sum_exec_runtime; > > > + sig->sum_sched_runtime += read_sum_exec_runtime(tsk); > > > sig->nr_threads--; > > > __unhash_process(tsk, group_dead); > > > write_sequnlock(&sig->stats_lock); > > > > If I'm not mistaken, at this point @p is dead, sum_exec_runtime will not > > ever be updated again. > > I think at this point find_task_by_vpid() will still return not-null > pointer, hence we can update sum_exec_runtime via: > > posix_cpu_{clock_get(),timer_set(),timer_get()} -> > cpu_clock_sample() -> task_sched_runtime() -> update_curr() > > if some thread will do cpuclock/cputimer related syscall for > different thread and CPUCLOCK_SCHED clock. Ah, ok. I always forget how the exit path works.. > > > diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c > > > index 39008d7..a2d753b 100644 > > > --- a/kernel/time/posix-cpu-timers.c > > > +++ b/kernel/time/posix-cpu-timers.c > > > @@ -848,7 +848,7 @@ static void check_thread_timers(struct task_struct *tsk, > > > tsk_expires->virt_exp = expires_to_cputime(expires); > > > > > > tsk_expires->sched_exp = check_timers_list(++timers, firing, > > > - tsk->se.sum_exec_runtime); > > > + read_sum_exec_runtime(tsk)); > > > > > > /* > > > * Check for the special case thread timers. > > > > @tsk == current and IRQs are disabled, sum_exec_runtime cannot be > > updated. > > It still can be updated via syscalls on different thread, same paths > as above. Yep, realized that over-night.