Backport of CSI: set mounts in alloc hook resources atomically into release/1.4.x #16773
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Backport
This PR is auto-generated from #16722 to be assessed for backporting due to the inclusion of the label backport/1.4.x.
The below text is copied from the body of the original PR.
Fixes #16623
The allocrunner has a facility for passing data written by allocrunner hooks to taskrunner hooks. Currently the only consumers of this facility are the allocrunner CSI hook (which writes data) and the taskrunner volume hook (which reads that same data).
The allocrunner hook for CSI volumes doesn't set the alloc hook resources atomically. Instead, it gets the current resources and then writes a new version back. Because the CSI hook is currently the only writer and all readers happen long afterwards, this should be safe but #16623 shows there's some sequence of events during restore where this breaks down.
Refactor hook resources so that hook data is accessed via setters and getters that hold the mutex, and ensure the object is instantiated synchronously at the time the
AllocRunneris created.Note to reviewers: the reproduction for the crash is extremely complicated and timing dependent, so we're not going to be able to test this in a unit test. See my comment at #16623 (comment) for how this has been manually tested. There's some follow-up work we're going to need to do in #16746