From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f200.google.com (mail-pf0-f200.google.com [209.85.192.200]) by kanga.kvack.org (Postfix) with ESMTP id 057106B0038 for ; Mon, 6 Nov 2017 11:24:25 -0500 (EST) Received: by mail-pf0-f200.google.com with SMTP id b85so11474232pfj.22 for ; Mon, 06 Nov 2017 08:24:24 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id e33si4205182pld.533.2017.11.06.08.24.23 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 06 Nov 2017 08:24:24 -0800 (PST) Date: Mon, 6 Nov 2017 17:24:20 +0100 From: Michal Hocko Subject: Re: [PATCH] mm: do not rely on preempt_count in print_vma_addr Message-ID: <20171106162420.lrt2n524fwn6u4ev@dhcp22.suse.cz> References: <20171103110245.7049460a05cc18c7e8a9feb2@linux-foundation.org> <1509739786.2473.33.camel@wdc.com> <20171105081946.yr2pvalbegxygcky@dhcp22.suse.cz> <20171106100558.GD3165@worktop.lehotels.local> <20171106104354.2jlgd2m4j4gxx4qo@dhcp22.suse.cz> <20171106120025.GH3165@worktop.lehotels.local> <20171106121222.nnzrr4cb7s7y5h74@dhcp22.suse.cz> <20171106134031.g6dbelg55mrbyc6i@dhcp22.suse.cz> <8665ccad-fa48-b835-c2e0-e50a4f05f319@alibaba-inc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8665ccad-fa48-b835-c2e0-e50a4f05f319@alibaba-inc.com> Sender: owner-linux-mm@kvack.org List-ID: To: Yang Shi Cc: Peter Zijlstra , Bart Van Assche , "akpm@linux-foundation.org" , "joe@perches.com" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "mingo@redhat.com" On Tue 07-11-17 00:16:58, Yang Shi wrote: > > > On 11/6/17 5:40 AM, Michal Hocko wrote: > > On Mon 06-11-17 13:12:22, Michal Hocko wrote: > > > On Mon 06-11-17 13:00:25, Peter Zijlstra wrote: > > > > On Mon, Nov 06, 2017 at 11:43:54AM +0100, Michal Hocko wrote: > > > > > > Yes the comment is very much accurate. > > > > > > > > > > Which suggests that print_vma_addr might be problematic, right? > > > > > Shouldn't we do trylock on mmap_sem instead? > > > > > > > > Yes that's complete rubbish. trylock will get spurious failures to print > > > > when the lock is contended. > > > > > > Yes, but I guess that it is acceptable to to not print the state under > > > that condition. > > > > So what do you think about this? I think this is more robust than > > playing tricks with the explicit preempt count checks and less tedious > > than checking to make it conditional on the context. This is on top of > > Linus tree and if accepted it should replace the patch discussed here. > > --- > > From 0de6d57cbc54ee2686d1f1e4ffcc4ed490ded8aa Mon Sep 17 00:00:00 2001 > > From: Michal Hocko > > Date: Mon, 6 Nov 2017 14:31:20 +0100 > > Subject: [PATCH] mm: do not rely on preempt_count in print_vma_addr > > > > The preempt count check on print_vma_addr has been added by e8bff74afbdb > > ("x86: fix "BUG: sleeping function called from invalid context" in > > print_vma_addr()") and it relied on the elevated preempt count from > > preempt_conditional_sti because preempt_count check doesn't work on > > non preemptive kernels by default. The code has evolved though and > > d99e1bd175f4 ("x86/entry/traps: Refactor preemption and interrupt flag > > handling") has replaced preempt_conditional_sti by an explicit > > preempt_disable which is noop on !PREEMPT so the check in print_vma_addr > > is broken. > > > > Fix the issue by using trylock on mmap_sem rather than chacking the > > s/chacking/checking ups, fixed > > preempt count. The allocation we are relying on has to be GFP_NOWAIT > > as well. There is a chance that we won't dump the vma state if the lock > > is contended or the memory short but this is acceptable outcome and much > > less fragile than the not working preemption check or tricks around it. > > > > Fixes: d99e1bd175f4 ("x86/entry/traps: Refactor preemption and interrupt flag handling") > > Signed-off-by: Michal Hocko > > Acked-by: Yang Shi Thanks! -- Michal Hocko SUSE Labs -- 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/ . Don't email: email@kvack.org