linux-kernel - Re: sysfs: use a separate locking class for open files depending on mmap

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Date:	Tue, 3 Dec 2013 13:43:24 -0500
From:	Dave Jones <davej@...hat.com>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	tj@...nel.org, gregkh@...uxfoundation.org
Subject: Re: sysfs: use a separate locking class for open files depending on
 mmap

On Thu, Nov 28, 2013 at 05:12:23AM +0000, Linux Kernel wrote:
 > Gitweb:     http://git.kernel.org/linus/;a=commit;h=027a485d12e089314360d459b8d847104dd28702
 > Commit:     027a485d12e089314360d459b8d847104dd28702
 > Parent:     54d71145a4548330313ca664a4a009772fe8b7dd
 > Author:     Tejun Heo <tj@...nel.org>
 > AuthorDate: Sun Nov 17 11:17:36 2013 +0900
 > Committer:  Greg Kroah-Hartman <gregkh@...uxfoundation.org>
 > CommitDate: Sat Nov 23 10:52:13 2013 -0800
 > 
 >     sysfs: use a separate locking class for open files depending on mmap
 >     
 >     The following two commits implemented mmap support in the regular file
 >     path and merged bin file support into the regular path.
 > ...
 > -	mutex_init(&of->mutex);
 > +	/*
 > +	 * The following is done to give a different lockdep key to
 > +	 * @of->mutex for files which implement mmap.  This is a rather
 > +	 * crude way to avoid false positive lockdep warning around
 > +	 * mm->mmap_sem - mmap nests @of->mutex under mm->mmap_sem and
 > +	 * reading /sys/block/sda/trace/act_mask grabs sr_mutex, under
 > +	 * which mm->mmap_sem nests, while holding @of->mutex.  As each
 > +	 * open file has a separate mutex, it's okay as long as those don't
 > +	 * happen on the same file.  At this point, we can't easily give
 > +	 * each file a separate locking class.  Let's differentiate on
 > +	 * whether the file has mmap or not for now.
 > +	 */
 > +	if (has_mmap)
 > +		mutex_init(&of->mutex);
 > +	else
 > +		mutex_init(&of->mutex);
 > +
 
Somehow I just triggered this trace again, even with this commit applied.
The trace is pretty much identical to the old one.

	Dave

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