linux-kernel - Re: [PATCH v3 01/22] timer: Allow to check when the timer callback has not finished yet

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Date:	Wed, 18 Nov 2015 23:32:28 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Petr Mladek <pmladek@...e.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>, Tejun Heo <tj@...nel.org>,
	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>,
	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>, linux-api@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 01/22] timer: Allow to check when the timer callback
 has not finished yet

On Wed, 18 Nov 2015, Petr Mladek wrote:
> timer_pending() checks whether the list of callbacks is empty.
> Each callback is removed from the list before it is called,
> see call_timer_fn() in __run_timers().
> 
> Sometimes we need to make sure that the callback has finished.
> For example, if we want to free some resources that are accessed
> by the callback.
> 
> For this purpose, this patch adds timer_active(). It checks both
> the list of callbacks and the running_timer. It takes the base_lock
> to see a consistent state.
> 
> I plan to use it to implement delayed works in kthread worker.
> But I guess that it will have wider use. In fact, I wonder if
> timer_pending() is misused in some situations.

Well. That's nice and good. But how will that new function solve
anything? After you drop the lock the state is not longer valid.
 
Thanks,

	tglx
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