Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753368AbaJTJNW (ORCPT ); Mon, 20 Oct 2014 05:13:22 -0400 Received: from casper.infradead.org ([85.118.1.10]:44135 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752815AbaJTJNS (ORCPT ); Mon, 20 Oct 2014 05:13:18 -0400 Date: Mon, 20 Oct 2014 11:13:11 +0200 From: Peter Zijlstra To: Oleg Nesterov Cc: Kirill Tkhai , Kirill Tkhai , "linux-kernel@vger.kernel.org" , Ingo Molnar , Vladimir Davydov Subject: Re: [PATCH] sched/numa: fix unsafe get_task_struct() in task_numa_assign() Message-ID: <20141020091311.GC3219@twins.programming.kicks-ass.net> References: <1413376300.24793.55.camel@tkhai> <20141017213641.GB32576@redhat.com> <4323181413620101@web21o.yandex.ru> <20141018205614.GA15934@redhat.com> <33631413674011@web7o.yandex.ru> <20141019192437.GA842@redhat.com> <20141019193744.GA3097@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141019193744.GA3097@redhat.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org OK, I think I'm finally awake enough to see what you're all talking about :-) On Sun, Oct 19, 2014 at 09:37:44PM +0200, Oleg Nesterov wrote: > > > RT tree has: > > > > > > https://git.kernel.org/cgit/linux/kernel/git/paulg/3.10-rt-patches.git/ > > > tree/patches/sched-delay-put-task.patch (answering the other email asking about this) RT does this because we call put_task_struct() with preempt disabled and on RT the memory allocator has sleeping locks. > > Yes, and this obviously implies more rcu callbacks in flight, and another > > gp before __put_task_struct(). but may be we will need to do this anyway... > > Forgot to mention... Or we can make task_struct_cachep SLAB_DESTROY_BY_RCU, > in this case ->curr (or any other "task_struct *" ponter) can not go away > under rcu_read_lock(). task_numa_compare() still needs the PF_EXITING check, > but we do not need to recheck ->curr or probe_kernel_read(). I think I would prefer SLAB_DESTROY_BY_RCU for this, because as you pointed out, I'm not sure mainline would like the extra callbacks. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/