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

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Message-ID: <1365179211.4530.9.camel@marge.simpson.net>
Date:	Fri, 05 Apr 2013 18:26:51 +0200
From:	Mike Galbraith <bitbucket@...ine.de>
To:	Rik van Riel <riel@...riel.com>
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 Fri, 2013-04-05 at 09:21 -0400, Rik van Riel wrote: 
> 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?

Running a model of a userspace task scheduler.  That was a fix or so ago
now though.  I'll try the set again on that box.

-Mike

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