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Description of problem:

This is a multi-part minor bug.

prepareToResizePhysical/Logical do their allocations wholly on a dm thread, not on a VDO thread. As such, they do not need to mark the layer as allocationsAllowed; their thread is registered with a NULL pointer to decide whether allocations are allowed, so they are always disallowed. Furthermore, a comment should be added that they may not do any work on threads, lest a allocation block on IO through VDO that requires the use of the blocked thread.

resizePhysical/Logical do no allocations, but have allocationsAllowed. The setting of allocationsAllowed is both no-effect currently, and dangerous: were there to be an allocation from something during the period currently allowed, it would potentially wait for a page to write out through the (suspended) VDO, deadlocking the thread allocating until the VDO were unsuspended.


Version-Release number of selected component (if applicable):
All

How reproducible:
Exceeding rare

Steps to Reproduce:
1. Wholly theoretical at this point

Actual results:
Possible deadlock

Expected results:
No deadlock

regression testing passed with vdo vdo-6.1.1.120-3.el7.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2018:3094