From: Tejun Heo <tj@kernel.org>
To: Chen Gang <gang.chen@asianux.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Oleg Nesterov <oleg@redhat.com>,
laijs@cn.fujitsu.com, Andrew Morton <akpm@linux-foundation.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] kernel/kthread.c: need spin_lock_irq() for 'worker' before main looping, since it can "WARN_ON(worker->task)".
Date: Wed, 19 Jun 2013 01:41:24 -0700 [thread overview]
Message-ID: <20130619084124.GF30681@mtj.dyndns.org> (raw)
In-Reply-To: <51C12D9A.8030801@asianux.com>
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.
Thanks.
--
tejun
next prev parent reply other threads:[~2013-06-19 8:41 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-06-19 4:03 [PATCH] kernel/kthread.c: need spin_lock_irq() for 'worker' before main looping, since it can "WARN_ON(worker->task)" Chen Gang
2013-06-19 8:41 ` Tejun Heo [this message]
2013-06-19 10:17 ` Chen Gang
2013-06-19 15:52 ` Tejun Heo
2013-06-20 1:53 ` Chen Gang
2013-06-20 7:02 ` Thomas Gleixner
2013-06-20 7:37 ` Chen Gang
2013-06-20 8:28 ` Thomas Gleixner
2013-06-20 9:36 ` Chen Gang
2013-06-19 8:43 ` Thomas Gleixner
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