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Message-ID: <20151007142446.GA2012@mtj.duckdns.org> Date: Wed, 7 Oct 2015 07:24:46 -0700 From: Tejun Heo <tj@...nel.org> To: Petr Mladek <pmladek@...e.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, Oleg Nesterov <oleg@...hat.com>, Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Steven Rostedt <rostedt@...dmis.org>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Josh Triplett <josh@...htriplett.org>, Thomas Gleixner <tglx@...utronix.de>, Linus Torvalds <torvalds@...ux-foundation.org>, Jiri Kosina <jkosina@...e.cz>, Borislav Petkov <bp@...e.de>, Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org, Vlastimil Babka <vbabka@...e.cz>, live-patching@...r.kernel.org, linux-api@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [RFC v2 07/18] kthread: Allow to cancel kthread work Hello, Petr. On Wed, Oct 07, 2015 at 11:21:30AM +0200, Petr Mladek wrote: > Now, let's have one work: W, two workers: A, B, and try to queue > the same work to the two workers at the same time: It's a debug WARN condition to catch silly mistakes. It can have minor race conditions. ... > Second, we still need the busy waiting for the pending timer callback. Isn't that del_timer_sync()? > Yes, we could set some flag so that the call back does not queue > the work. But cancel_kthread_work_sync() still has to wait. > It could not return if there is still some pending operation > with the struct kthread_work. Otherwise, it never could > be freed a safe way. > > Also note that we still need the WORK_PENDING flag. Otherwise, we > would not be able to detect the race when timer is removed but > the callback has not run yet. Yeah, just use a state field as I wrote before. > Let me to repeat that using per-work and per-worker lock is not an > option either. We would need some crazy hacks to avoid ABBA deadlocks. > > > All in all, I would prefer to keep the original approach that is > heavily inspired by the workqueues. I think that it is actually > an advantage to reuse some working concept that reinventing wheels. At each turn, you come up with non-issues and declare that it needs to be full workqueue-like implementation but the issues you're raising seem all rather irrelevant. Can you please try to take a step back and put some distance from the implementation details of workqueue? Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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