From: Petr Mladek <pmladek@suse.com> To: Tejun Heo <tj@kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org>, Oleg Nesterov <oleg@redhat.com>, Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>, Steven Rostedt <rostedt@goodmis.org>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, Josh Triplett <josh@joshtriplett.org>, Thomas Gleixner <tglx@linutronix.de>, Linus Torvalds <torvalds@linux-foundation.org>, Jiri Kosina <jkosina@suse.cz>, Borislav Petkov <bp@suse.de>, Michal Hocko <mhocko@suse.cz>, linux-mm@kvack.org, Vlastimil Babka <vbabka@suse.cz>, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 09/22] kthread: Allow to cancel kthread work Date: Fri, 19 Feb 2016 17:22:39 +0100 [thread overview] Message-ID: <20160219162239.GT3305@pathway.suse.cz> (raw) In-Reply-To: <20160125191709.GE3628@mtj.duckdns.org> On Mon 2016-01-25 14:17:09, Tejun Heo wrote: > On Mon, Jan 25, 2016 at 04:44:58PM +0100, Petr Mladek wrote: > > +static bool __cancel_kthread_work_sync(struct kthread_work *work) [...] > > + work->canceling++; > > + ret = try_to_cancel_kthread_work(work, &worker->lock, &flags); > > + > > + if (worker->current_work != work) > > + goto out_fast; > > If there are two racing cancellers, wouldn't this allow the losing one > to return while the work item is still running? If the work is running, worker->current_work must point to it. All cancelers will see it and queue its own kthread_flush_work. It is a bit sub-optimal but it is trivial. I doubt that there will be many parallel cancelers in practice. > > + spin_unlock_irqrestore(&worker->lock, flags); > > + flush_kthread_work(work); > > + /* > > + * Nobody is allowed to switch the worker or queue the work > > + * when .canceling is set. > > + */ > > + spin_lock_irqsave(&worker->lock, flags); > > + > > +out_fast: > > + work->canceling--; > > + spin_unlock_irqrestore(&worker->lock, flags); > > +out: > > + return ret; Best Regards, Petr PS: I have updated the patchset according to your other comments. In addition, I got rid of many try_lock games. We do not allow to queue the same work to different workers. Therefore it should be enough to warn if the worker changes unexpectedly. It makes the code even more simple. I still need to do some testing. I will send it next week, hopefully.
WARNING: multiple messages have this Message-ID (diff)
From: Petr Mladek <pmladek@suse.com> To: Tejun Heo <tj@kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org>, Oleg Nesterov <oleg@redhat.com>, Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>, Steven Rostedt <rostedt@goodmis.org>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, Josh Triplett <josh@joshtriplett.org>, Thomas Gleixner <tglx@linutronix.de>, Linus Torvalds <torvalds@linux-foundation.org>, Jiri Kosina <jkosina@suse.cz>, Borislav Petkov <bp@suse.de>, Michal Hocko <mhocko@suse.cz>, linux-mm@kvack.org, Vlastimil Babka <vbabka@suse.cz>, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 09/22] kthread: Allow to cancel kthread work Date: Fri, 19 Feb 2016 17:22:39 +0100 [thread overview] Message-ID: <20160219162239.GT3305@pathway.suse.cz> (raw) In-Reply-To: <20160125191709.GE3628@mtj.duckdns.org> On Mon 2016-01-25 14:17:09, Tejun Heo wrote: > On Mon, Jan 25, 2016 at 04:44:58PM +0100, Petr Mladek wrote: > > +static bool __cancel_kthread_work_sync(struct kthread_work *work) [...] > > + work->canceling++; > > + ret = try_to_cancel_kthread_work(work, &worker->lock, &flags); > > + > > + if (worker->current_work != work) > > + goto out_fast; > > If there are two racing cancellers, wouldn't this allow the losing one > to return while the work item is still running? If the work is running, worker->current_work must point to it. All cancelers will see it and queue its own kthread_flush_work. It is a bit sub-optimal but it is trivial. I doubt that there will be many parallel cancelers in practice. > > + spin_unlock_irqrestore(&worker->lock, flags); > > + flush_kthread_work(work); > > + /* > > + * Nobody is allowed to switch the worker or queue the work > > + * when .canceling is set. > > + */ > > + spin_lock_irqsave(&worker->lock, flags); > > + > > +out_fast: > > + work->canceling--; > > + spin_unlock_irqrestore(&worker->lock, flags); > > +out: > > + return ret; Best Regards, Petr PS: I have updated the patchset according to your other comments. In addition, I got rid of many try_lock games. We do not allow to queue the same work to different workers. Therefore it should be enough to warn if the worker changes unexpectedly. It makes the code even more simple. I still need to do some testing. I will send it next week, hopefully. -- 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: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2016-02-19 16:22 UTC|newest] Thread overview: 82+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-01-25 15:44 [PATCH v4 00/22] kthread: Use kthread worker API more widely Petr Mladek 2016-01-25 15:44 ` Petr Mladek 2016-01-25 15:44 ` Petr Mladek 2016-01-25 15:44 ` [PATCH v4 01/22] timer: Allow to check when the timer callback has not finished yet Petr Mladek 2016-01-25 15:44 ` Petr Mladek 2016-01-25 18:44 ` Tejun Heo 2016-01-25 18:44 ` Tejun Heo 2016-01-25 15:44 ` [PATCH v4 02/22] kthread/smpboot: Do not park in kthread_create_on_cpu() Petr Mladek 2016-01-25 15:44 ` Petr Mladek 2016-01-25 15:44 ` [PATCH v4 03/22] kthread: Allow to call __kthread_create_on_node() with va_list args Petr Mladek 2016-01-25 15:44 ` Petr Mladek 2016-01-25 15:44 ` [PATCH v4 04/22] kthread: Add create_kthread_worker*() Petr Mladek 2016-01-25 15:44 ` Petr Mladek 2016-01-25 18:53 ` Tejun Heo 2016-01-25 18:53 ` Tejun Heo 2016-02-16 15:44 ` Petr Mladek 2016-02-16 15:44 ` Petr Mladek 2016-02-16 16:08 ` Tejun Heo 2016-02-16 16:08 ` Tejun Heo 2016-02-16 16:08 ` Tejun Heo 2016-02-16 16:10 ` Petr Mladek 2016-02-16 16:10 ` Petr Mladek 2016-02-16 16:10 ` Petr Mladek 2016-01-25 15:44 ` [PATCH v4 05/22] kthread: Add drain_kthread_worker() Petr Mladek 2016-01-25 15:44 ` Petr Mladek 2016-01-25 15:44 ` [PATCH v4 06/22] kthread: Add destroy_kthread_worker() Petr Mladek 2016-01-25 15:44 ` Petr Mladek 2016-01-25 15:44 ` [PATCH v4 07/22] kthread: Detect when a kthread work is used by more workers Petr Mladek 2016-01-25 15:44 ` Petr Mladek 2016-01-25 18:57 ` Tejun Heo 2016-01-25 18:57 ` Tejun Heo 2016-01-25 18:57 ` Tejun Heo 2016-02-16 16:38 ` Petr Mladek 2016-02-16 16:38 ` Petr Mladek 2016-02-16 16:38 ` Petr Mladek 2016-01-25 15:44 ` [PATCH v4 08/22] kthread: Initial support for delayed kthread work Petr Mladek 2016-01-25 15:44 ` Petr Mladek 2016-01-25 19:04 ` Tejun Heo 2016-01-25 19:04 ` Tejun Heo 2016-01-25 19:04 ` Tejun Heo 2016-01-25 15:44 ` [PATCH v4 09/22] kthread: Allow to cancel " Petr Mladek 2016-01-25 15:44 ` Petr Mladek 2016-01-25 19:17 ` Tejun Heo 2016-01-25 19:17 ` Tejun Heo 2016-02-19 16:22 ` Petr Mladek [this message] 2016-02-19 16:22 ` Petr Mladek 2016-01-25 15:44 ` [PATCH v4 10/22] kthread: Allow to modify delayed " Petr Mladek 2016-01-25 15:44 ` Petr Mladek 2016-01-25 19:19 ` Tejun Heo 2016-01-25 19:19 ` Tejun Heo 2016-01-25 15:45 ` [PATCH v4 11/22] kthread: Better support freezable kthread workers Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 19:21 ` Tejun Heo 2016-01-25 19:21 ` Tejun Heo 2016-01-25 15:45 ` [PATCH v4 12/22] kthread: Use try_lock_kthread_work() in flush_kthread_work() Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 15:45 ` [PATCH v4 13/22] mm/huge_page: Convert khugepaged() into kthread worker API Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 15:45 ` [PATCH v4 14/22] ring_buffer: Convert benchmark kthreads " Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 15:45 ` [PATCH v4 15/22] hung_task: Convert hungtaskd " Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 15:45 ` [PATCH v4 16/22] kmemleak: Convert kmemleak kthread " Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 15:45 ` [PATCH v4 17/22] ipmi: Convert kipmi " Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 15:45 ` [PATCH v4 18/22] IB/fmr_pool: Convert the cleanup thread " Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 15:45 ` [PATCH v4 19/22] memstick/r592: Better synchronize debug messages in r592_io kthread Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 15:45 ` [PATCH v4 20/22] memstick/r592: convert r592_io kthread into kthread worker API Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 15:45 ` [PATCH v4 21/22] thermal/intel_powerclamp: Remove duplicated code that starts the kthread Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 16:23 ` Jacob Pan 2016-01-25 16:23 ` Jacob Pan 2016-01-25 15:45 ` [PATCH v4 22/22] thermal/intel_powerclamp: Convert the kthread to kthread worker API Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 16:28 ` Jacob Pan 2016-01-25 16:28 ` Jacob Pan
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