linux-kernel - Re: [PATCH v3 09/22] kthread: Allow to cancel kthread work

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Message-ID: <20151124202855.GV17033@mtj.duckdns.org>
Date:	Tue, 24 Nov 2015 15:28:55 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Petr Mladek <pmladek@...e.com>,
	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>,
	Jiri Kosina <jkosina@...e.cz>, Borislav Petkov <bp@...e.de>,
	Michal Hocko <mhocko@...e.cz>, linux-mm <linux-mm@...ck.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Linux API <linux-api@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 09/22] kthread: Allow to cancel kthread work

Hello,

On Tue, Nov 24, 2015 at 12:23:53PM -0800, Linus Torvalds wrote:
> instead (possibly just "spin_unlock_wait()" - but the explicit loop

I see.  Wasn't thinking about cache traffic.  Yeah, spin_unlock_wait()
seems a lot better.

> might be worth it if you then want to check the "canceling" flag
> independently of the lock state too).
> 
> In general, it's very dangerous to try to cook up your own locking
> rules. People *always* get it wrong.

It's either trylock on timer side or timer active spinning trick on
canceling side, so this seems the lesser of the two evils.

Thanks.

-- 
tejun
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