From: Theodore Ts'o <tytso@mit.edu>
Subject: Re: 4.7.0-rc7 ext4 error in dx_probe
Date: Mon, 8 Aug 2016 12:08:18 -0400
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Cc: Johannes Stezenbach <js@sig21.net>,
	=?iso-8859-1?B?VPZy9ms=?= Edwin <edwin@etorok.net>,
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To: "Darrick J. Wong" <darrick.wong@oracle.com>
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On Sun, Aug 07, 2016 at 11:28:10PM -0700, Darrick J. Wong wrote:
> 
> I have one lingering concern -- is it a bug that two processes could be
> computing the checksum of a buffer simultaneously?  I would have thought ext4
> would serialize that kind of buffer_head access...

Do we know how this is happening?  We've always depended on the VFS to
provide this exclusion.  The only way we should be modifying the
buffer_head at the same time if two CPU's are trying to modify the
directory at the same time, and that should _never_ be happening, even
with the new directory parallism code, unless the file system has
given permission and intends to do its own fine-grained locking.

      		     	     	       	   - Ted