[PATCH 0/3 v2] [SRU] [bionic/linux-azure-4.15] CIFS open/close race fixes

[Tim Gardner]

[Impact]
Microsoft has asked for these 3 patches to be applied to the linux-azure-4.15 kernel.
The code has changed significantly from 4.15 to 5.6, so the patches are
quite different then current upstream. Hopefully I've captured the intent
if not the function in those patches.

v2 - ran scripts/checkpatch.pl and corrected formatting errors. No logic changes.

[1] - Correct corner case where a close operation does not complete.
[2] - Fix a race when an OPEN is cancelled.
[3] - Fix a panic when allocating memory when a spinlock is held.

[Test Case]
none

[Potential regression]
These patches are all intended to accomodate boundary conditions. You shouldn't
experience any regression under normal use.