From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f71.google.com (mail-wm0-f71.google.com [74.125.82.71]) by kanga.kvack.org (Postfix) with ESMTP id 9416B6B0033 for ; Tue, 7 Feb 2017 05:35:55 -0500 (EST) Received: by mail-wm0-f71.google.com with SMTP id u63so24540930wmu.0 for ; Tue, 07 Feb 2017 02:35:55 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id 140si11665616wmt.40.2017.02.07.02.35.54 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 07 Feb 2017 02:35:54 -0800 (PST) Date: Tue, 7 Feb 2017 11:35:52 +0100 From: Michal Hocko Subject: Re: mm: deadlock between get_online_cpus/pcpu_alloc Message-ID: <20170207103552.GH5065@dhcp22.suse.cz> References: <20170206220530.apvuknbagaf2rdlw@techsingularity.net> <20170207084855.GC5065@dhcp22.suse.cz> <20170207094300.cuxfqi35wflk5nr5@techsingularity.net> <2cdef192-1939-d692-1224-8ff7d7ff7203@suse.cz> <20170207102809.awh22urqmfrav5r6@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170207102809.awh22urqmfrav5r6@techsingularity.net> Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Vlastimil Babka , Dmitry Vyukov , Tejun Heo , Christoph Lameter , "linux-mm@kvack.org" , LKML , Thomas Gleixner , Ingo Molnar , Peter Zijlstra , syzkaller , Andrew Morton On Tue 07-02-17 10:28:09, Mel Gorman wrote: > On Tue, Feb 07, 2017 at 10:49:28AM +0100, Vlastimil Babka wrote: > > On 02/07/2017 10:43 AM, Mel Gorman wrote: > > > If I'm reading this right, a hot-remove will set the pool POOL_DISASSOCIATED > > > and unbound. A workqueue queued for draining get migrated during hot-remove > > > and a drain operation will execute twice on a CPU -- one for what was > > > queued and a second time for the CPU it was migrated from. It should still > > > work with flush_work which doesn't appear to block forever if an item > > > got migrated to another workqueue. The actual drain workqueue function is > > > using the CPU ID it's currently running on so it shouldn't get confused. > > > > Is the worker that will process this migrated workqueue also guaranteed > > to be pinned to a cpu for the whole work, though? drain_local_pages() > > needs that guarantee. > > > > It should be by running on a workqueue handler bound to that CPU (queued > on wq->cpu_pwqs in __queue_work) Are you sure? The comment in kernel/workqueue.c says * While DISASSOCIATED, the cpu may be offline and all workers have * %WORKER_UNBOUND set and concurrency management disabled, and may * be executing on any CPU. The pool behaves as an unbound one. I might be misreadig but an unbound pool can be handled by workers which are not pinned on any cpu AFAIU. -- 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