[XFS] Block on unwritten extent conversion during synchronous direct I/O.
[XFS] Block on unwritten extent conversion during synchronous direct I/O.

Currently we do not wait on extent conversion to occur, and hence we can
return to userspace from a synchronous direct I/O write without having
completed all the actions in the write. Hence a read after the write may
see zeroes (unwritten extent) rather than the data that was written.

Block the I/O completion by triggering a synchronous workqueue flush to
ensure that the conversion has occurred before we return to userspace.

SGI-PV: 964092
SGI-Modid: xfs-linux-melb:xfs-kern:28775a

Signed-off-by: David Chinner <d2f98f0f27147ca85564d32aa37577d3673e6910@sgi.com>
Signed-off-by: Tim Shimmin <d1c056a983786a38ca76a05cda240c7b86d77136@sgi.com>

KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs