linux-kernel - Re: [PATCH v3] futex: Remove requirement for lock

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Message-ID: <20160120202059.GH27825@linux-uzut.site>
Date:	Wed, 20 Jan 2016 12:20:59 -0800
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Mel Gorman <mgorman@...hsingularity.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Chris Mason <clm@...com>, Darren Hart <dvhart@...ux.intel.com>,
	linux-kernel@...r.kernel.org, Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH v3] futex: Remove requirement for lock_page in

On Wed, 20 Jan 2016, Thomas Gleixner wrote:

>On Wed, 20 Jan 2016, Davidlohr Bueso wrote:
>> On Tue, 19 Jan 2016, Bueso wrote:
>> > +
>> > +		/* Should be impossible but lets be paranoid for now */
>> > +		BUG_ON(inode->i_mapping != mapping);
>>
>> Hmm, do we want to transform this into an if and do rcu unlock and then just
>> call BUG()? I't doesn't matter at this point _anyway_, but it would be the
>> right
>> thing to do, no?
>
>The better solution is to err out gracefully.
>
>    	   if (WARN_ON_ONCE(inode->i_mapping != mapping) {
>	      	   err = -EFAULT;
>		   rcu_read_unlock();
>		   goto out;
>    	   }
>
>Hmm?

Ok, Linus would probably like that as well. If we're going this way,
we also need to release inode reference, before the rcu unlock.

Thanks,
Davidlohr