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