linux-kernel - Re: [PATCH -mm -next] ipc,sem: untangle RCU locking with find_alloc

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Message-ID: <515ECFD0.4090202@surriel.com>
Date:	Fri, 05 Apr 2013 09:21:20 -0400
From:	Rik van Riel <riel@...riel.com>
To:	Mike Galbraith <bitbucket@...ine.de>
CC:	Sasha Levin <sasha.levin@...cle.com>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, hhuang@...hat.com, jason.low2@...com,
	walken@...gle.com, lwoodman@...hat.com, chegu_vinod@...com,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH -mm -next] ipc,sem: untangle RCU locking with find_alloc_undo

On 04/05/2013 12:38 AM, Mike Galbraith wrote:
> On Tue, 2013-03-26 at 16:00 -0400, Rik van Riel wrote:

>> The ipc semaphore code has a nasty RCU locking tangle, with both
>> find_alloc_undo and semtimedop taking the rcu_read_lock(). The
>> code can be cleaned up somewhat by only taking the rcu_read_lock
>> once.
>>
>> There are no other callers to find_alloc_undo.
>>
>> This should also solve the trinity issue reported by Sasha Levin.
>
> I take it this is on top of the patchlet Sasha submitted?

Indeed, and all the other fixes that got submitted :)

> (I hit rcu stall banging on patch set in rt with 60 synchronized core
> executive model if I let it run long enough, fwtw)

What are you using to trigger an rcu stall?

>> Reported-by: Sasha Levin <sasha.levin@...cle.com>
>> Signed-off-by: Rik van Riel <riel@...hat.com>

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