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Date: Wed, 19 Jun 2013 18:17:36 +0800 From: Chen Gang <gang.chen@...anux.com> To: Tejun Heo <tj@...nel.org> CC: Thomas Gleixner <tglx@...utronix.de>, Oleg Nesterov <oleg@...hat.com>, laijs@...fujitsu.com, Andrew Morton <akpm@...ux-foundation.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] kernel/kthread.c: need spin_lock_irq() for 'worker' before main looping, since it can "WARN_ON(worker->task)". On 06/19/2013 04:41 PM, Tejun Heo wrote: > On Wed, Jun 19, 2013 at 12:03:38PM +0800, Chen Gang wrote: >> > >> > Since "WARN_ON(worker->task)", we can not assume that 'worker->task' >> > will be NULL before set 'current' to it. >> > >> > So need let 'worker' lock protected too, just like it already lock >> > protected all time in main looping. > That synchronization is the kthread_worker user's responsibility. The > locking around worker->task = NULL is to prevent the worker task being > destroyed while insert_kthread_work() is trying to wake it up. It has > nothing to do with the user trying to attach multiple tasks to the > same kthread_worker. Plus, putting locking around WARN_ON() is > pointless. It doesn't really fix anything. It just makes WARN_ON() > trigger *slightly* more reliably. Hmm... can 'worker->task' has chance to be not NULL before set 'current' to it ? why do we use WARN_ON(worker->task) ? I guess it still has chance to let "worker->task != NULL", or it should be BUG_ON(worker->task) instead of. Thanks. -- Chen Gang Asianux Corporation -- 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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