Message-ID: <1365179211.4530.9.camel@marge.simpson.net>
Subject: Re: [PATCH -mm -next] ipc,sem: untangle RCU locking with
 find_alloc_undo
From: Mike Galbraith <bitbucket@online.de>
To: Rik van Riel <riel@surriel.com>
Cc: Sasha Levin <sasha.levin@oracle.com>,
        Davidlohr Bueso <davidlohr.bueso@hp.com>,
        torvalds@linux-foundation.org, linux-kernel@vger.kernel.org,
        akpm@linux-foundation.org, hhuang@redhat.com, jason.low2@hp.com,
        walken@google.com, lwoodman@redhat.com, chegu_vinod@hp.com,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Date: Fri, 05 Apr 2013 18:26:51 +0200
In-Reply-To: <515ECFD0.4090202@surriel.com>
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	 <5151E3D2.1070103@oracle.com>
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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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