Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754304AbaBLVOb (ORCPT ); Wed, 12 Feb 2014 16:14:31 -0500 Received: from zeniv.linux.org.uk ([195.92.253.2]:45321 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753776AbaBLVOa (ORCPT ); Wed, 12 Feb 2014 16:14:30 -0500 Date: Wed, 12 Feb 2014 21:14:22 +0000 From: Al Viro To: Linus Torvalds Cc: Dave Chinner , Dave Jones , Eric Sandeen , Linux Kernel , xfs@oss.sgi.com Subject: Re: 3.14-rc2 XFS backtrace because irqs_disabled. Message-ID: <20140212211421.GP18016@ZenIV.linux.org.uk> References: <52FA9ADA.9040803@sandeen.net> <20140212004403.GA17129@redhat.com> <20140212010941.GM18016@ZenIV.linux.org.uk> <20140212040358.GA25327@redhat.com> <20140212042215.GN18016@ZenIV.linux.org.uk> <20140212054043.GB13997@dastard> <20140212113928.GO18016@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 12, 2014 at 12:13:19PM -0800, Linus Torvalds wrote: > On Wed, Feb 12, 2014 at 3:39 AM, Al Viro wrote: > > On Tue, Feb 11, 2014 at 10:28:12PM -0800, Linus Torvalds wrote: > > > >> It looks like just "do_signal()" has a stack frame that is about 230 > >> bytes even under normal circumstancs (largely due to "struct ksignal" > >> - which in turn is largely due to the insane 128-byte padding in > >> siginfo_t). Add a few other frames in there, and I guess that if it > >> was close before, the coredump path just makes it go off. > > > > We could, in principle, put it into task_struct and make get_signal() > > return its address - do_signal() is called only in the code that does > > assorted returns to userland... > > We have better uses for random buffers in "struct task_struct", I'd > hate to put a siginfo_t there. *nod* > The thing is, siginfo_t has that idiotic 128-byte area, but it's all > "for future expansion". I think it's some damn glibc disease - we've > seen these kinds of insane paddings before. > > The actual *useful* part of siginfo_t is on the order of 32 bytes. If that. > > Sad. Umm... What if we delay __sigqueue_free()? After all, that's where the fat sucker normally comes from. That way we might get away with much smaller structure on stack... Just introduce a small structure that would contain signr, uid, pid and pointer to struct sigqueue. And pass a pointer to _that_ all the way down to collect_signal(). Pointer's NULL == it's SI_USER with signr/uid/pid from the small struct and all other fields are zero. Pointer isn't NULL - use &small_struct->p->info. And have struct sigqueue actually freed via task_work_add() in that case. Do you see any fundamental problems with that? Looks like it would be faster as well - less copying involved... -- 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/