linux-kernel - Re: hugetlb locking bug.

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Message-ID: <1302901625.2035.37.camel@laptop>
Date:	Fri, 15 Apr 2011 23:07:05 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	William Irwin <wli@...omorphy.com>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: hugetlb locking bug.

On Fri, 2011-04-15 at 13:49 -0700, Linus Torvalds wrote:
> Hmm. Adding the hugetlbfs/lockdep people to the cc.
> 
> This _looks_ like the same kind of false positive we've had with some
> other cases: we're taking the i_mutex lock only dor directory inodes
> (for the readdir) and we take the i_mmap lock only for non-directory
> inodes, so you can't actually get any real circular locking issues.
> 
> So yes, we do mix the order of i_mmap_sem and i_mutex, but it's
> conceptually two "different" kinds of i_mutex that just happen to
> share a name.
> 
> And I really thought we annotated it as such with different
> "lockdep_set_class()" cases (ie the whole
> 
>   lockdep_set_class(&inode->i_mutex,&type->i_mutex_dir_key);
> 
> for the S_ISDIR case in unlock_new_inode().
> 
> Can somebody more alert than me see why this lockdep issue still
> triggers with hugetlbfs? 

afaict hugetlbfs doesn't actually end up calling unlock_new_inode()
which does the whole IS_DIR() lockdep annotation, but then I might have
gotten lost in the whole inode allocation dance.

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