From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f46.google.com (mail-pa0-f46.google.com [209.85.220.46]) by kanga.kvack.org (Postfix) with ESMTP id 9CDBF900021 for ; Tue, 28 Oct 2014 05:49:27 -0400 (EDT) Received: by mail-pa0-f46.google.com with SMTP id lf10so330761pab.33 for ; Tue, 28 Oct 2014 02:49:27 -0700 (PDT) Received: from mailout4.w1.samsung.com (mailout4.w1.samsung.com. [210.118.77.14]) by mx.google.com with ESMTPS id az17si777846pdb.198.2014.10.28.02.49.25 for (version=TLSv1 cipher=RC4-MD5 bits=128/128); Tue, 28 Oct 2014 02:49:26 -0700 (PDT) Received: from eucpsbgm1.samsung.com (unknown [203.254.199.244]) by mailout4.w1.samsung.com (Oracle Communications Messaging Server 7u4-24.01(7.0.4.24.0) 64bit (built Nov 17 2011)) with ESMTP id <0NE500K1SFEYW190@mailout4.w1.samsung.com> for linux-mm@kvack.org; Tue, 28 Oct 2014 09:52:10 +0000 (GMT) Message-id: <544F66A2.1080302@samsung.com> Date: Tue, 28 Oct 2014 10:49:22 +0100 From: Marek Szyprowski MIME-version: 1.0 Subject: Re: Deadlock with CMA and CPU hotplug References: <5447E210.8020902@codeaurora.org> In-reply-to: <5447E210.8020902@codeaurora.org> Content-type: text/plain; charset=utf-8; format=flowed Content-transfer-encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Laura Abbott , mgorman@suse.de, mina86@mina86.com Cc: linux-mm@kvack.org, Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, pratikp@codeaurora.org Hello, On 2014-10-22 18:57, Laura Abbott wrote: > We've run into a AB/BA deadlock situation involving a driver lock and > the CPU hotplug lock on a 3.10 based kernel. The situation is this: > > CPU 0 CPU 1 > ----- ---- > Start CPU hotplug > mutex_lock(&cpu_hotplug.lock) > Run CPU hotplug notifier > data for driver comes in > mutex_lock(&driver_lock) > driver calls dma_alloc_coherent > alloc_contig_range > lru_add_drain_all > get_online_cpus() > mutex_lock(&cpu_hotplug.lock) > > Driver hotplug notifier runs > mutex_lock(&driver_lock) > > The driver itself is out of tree right now[1] and we're looking at > ways to rework the driver. The best option for rework right now > though might result in some performance penalties. The size that's > being allocated can't easily be converted to an atomic allocation either > It seems like this might be a limitation of where CMA/ > dma_alloc_coherent could potentially be used and make drivers > unnecessarily aware of CPU hotplug locking. > > Does this seem like an actual problem that needs to be fixed or > is trying to use CMA in a CPU hotplug notifier path just asking > for trouble? IMHO doing any allocation without GFP_ATOMIC from a notifier is asking for problems. I always considered notifiers as callbacks that might be called directly from i.e. interrupts. I don't know much about your code, but maybe it would be possible to move the problematic code from a notifier to a separate worker or thread? Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland -- 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