linux-kernel - Re: 2.6.26-rc4: RIP __call_for_each

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Message-ID: <20080527133510.GV7712@kernel.dk>
Date:	Tue, 27 May 2008 15:35:10 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Alexey Dobriyan <adobriyan@...il.com>
Cc:	torvalds@...l.org, Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com
Subject: Re: 2.6.26-rc4: RIP __call_for_each_cic+0x20/0x50

On Tue, May 27 2008, Alexey Dobriyan wrote:
> On Sat, May 10, 2008 at 02:37:19PM +0400, Alexey Dobriyan wrote:
> > > > > > @@ -41,8 +41,8 @@ int put_io_context(struct io_context *ioc)
> > > > > >  		rcu_read_lock();
> > > > > >  		if (ioc->aic && ioc->aic->dtor)
> > > > > >  			ioc->aic->dtor(ioc->aic);
> > > > > > -		rcu_read_unlock();
> > > > > >  		cfq_dtor(ioc);
> > > > > > +		rcu_read_unlock();
> > > > > >  
> > > > > >  		kmem_cache_free(iocontext_cachep, ioc);
> > > > > >  		return 1;
> > > > > 
> > > > > This helps in sense that 3 times bulk cross-compiles finish to the end.
> > > > > You'll hear me if another such oops will resurface.
> > > > 
> > > > Still looking good?
> > > 
> > > Yup!
> > 
> > And this with patch in mainline, again with PREEMPT_RCU.
> 
> Ping, this happened again with 2.6.26-rc4 and PREEMPT_RCU.

Worrisome... Paul, would you mind taking a quick look at cfq
and see if you can detect why breaks with preempt rcu? It's
clearly a use-after-free symptom, but I don't see how it can
happen.

-- 
Jens Axboe

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