Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754512AbbKXOtt (ORCPT ); Tue, 24 Nov 2015 09:49:49 -0500 Received: from mail-yk0-f181.google.com ([209.85.160.181]:34925 "EHLO mail-yk0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754425AbbKXOtq (ORCPT ); Tue, 24 Nov 2015 09:49:46 -0500 Date: Tue, 24 Nov 2015 09:49:42 -0500 From: Tejun Heo To: Petr Mladek Cc: Andrew Morton , Oleg Nesterov , Ingo Molnar , Peter Zijlstra , Steven Rostedt , "Paul E. McKenney" , Josh Triplett , Thomas Gleixner , Linus Torvalds , Jiri Kosina , Borislav Petkov , Michal Hocko , linux-mm@kvack.org, Vlastimil Babka , linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 07/22] kthread: Detect when a kthread work is used by more workers Message-ID: <20151124144942.GC17033@mtj.duckdns.org> References: <1447853127-3461-1-git-send-email-pmladek@suse.com> <1447853127-3461-8-git-send-email-pmladek@suse.com> <20151123222703.GH19072@mtj.duckdns.org> <20151124100650.GF10750@pathway.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151124100650.GF10750@pathway.suse.cz> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1850 Lines: 60 Hello, Petr. On Tue, Nov 24, 2015 at 11:06:50AM +0100, Petr Mladek wrote: > > > @@ -610,6 +625,12 @@ repeat: > > > if (work) { > > > __set_current_state(TASK_RUNNING); > > > work->func(work); > > > + > > > + spin_lock_irq(&worker->lock); > > > + /* Allow to queue the work into another worker */ > > > + if (!kthread_work_pending(work)) > > > + work->worker = NULL; > > > + spin_unlock_irq(&worker->lock); > > > > Doesn't this mean that the work item can't be freed from its callback? > > That pattern tends to happen regularly. > > I am not sure if I understand your question. Do you mean switching > work->func during the life time of the struct kthread_work? This > should not be affected by the above code. So, something like the following. void my_work_fn(work) { struct my_struct *s = container_of(work, ...); do something with s; kfree(s); } and the queuer does struct my_struct *s = kmalloc(sizeof(*s)); init s and s->work; queue(&s->work); expecting s to be freed on completion. IOW, you can't expect the work item to remain accessible once the work function starts executing. > The above code allows to queue an _unused_ kthread_work into any > kthread_worker. For example, it is needed for khugepaged, > see http://marc.info/?l=linux-kernel&m=144785344924871&w=2 > The work is static but the worker can be started/stopped > (allocated/freed) repeatedly. It means that the work need > to be usable with many workers. But it is associated only > with one worker when being used. It can just re-init work items when it restarts workers, right? Thanks. -- tejun -- 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/