linux-kernel - Re: sched: memory corruption on completing completions

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Date:	Fri, 06 Feb 2015 20:30:35 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Davidlohr Bueso <dave@...olabs.net>,
	Sasha Levin <sasha.levin@...cle.com>,
	Waiman Long <Waiman.Long@...com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrey Ryabinin <a.ryabinin@...sung.com>,
	Dave Jones <davej@...emonkey.org.uk>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: sched: memory corruption on completing completions

On 02/06/2015 12:18 PM, Raghavendra K T wrote:
> On 02/06/2015 04:27 AM, Linus Torvalds wrote:
>> On Thu, Feb 5, 2015 at 2:37 PM, Davidlohr Bueso <dave@...olabs.net>
>> wrote:
>>>>
>>>> It is possible that the paravirt spinlocks could be saved by:
>>>>
>>>>   - moving the clearing of TICKET_SLOWPATH_FLAG into the fastpath
>>>> locking code.
>>>
>>> Ouch, to avoid deadlocks they explicitly need the unlock to occur before
>>> the slowpath tail flag is read.
>>
>> Well, just make the unlock do the actual real unlock operation
>> ("fastpath"), leaving the TICKET_SLOWPATH_FLAG alone. The unlock path
>> can *test* the flag and do whatever kicking it needs to get people
>> started again, but not clear it again.
>>
>
> This is definitely a good idea, will think more on this.
>

Just sent the patch with that idea, also keeping in mind that
head = tail may not hold good for trylock checking
(last unlock might have left TICKET_SLOWPATH_FLAG set)

http://article.gmane.org/gmane.linux.kernel/1883900

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