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uma: Avoid allocating buckets with the cross-domain lock held

Authored by markj on Nov 23 2020, 2:33 PM.



Allocation of a bucket can trigger a cross-domain free in the bucket
zone, e.g., if the per-CPU alloc bucket is empty, we free it and get
migrated to a remote domain. I believe this can lead to deadlocks,
since a bucket zone may allocate buckets from itself, or a pair of
bucket zones could be allocating from each other.

Fix the problem by dropping the cross-domain lock before allocating a
new bucket and handling refill races. I added a list of empty buckets
to ensure that we can make forward progress.

Diff Detail

rS FreeBSD src repository - subversion
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Event Timeline

markj requested review of this revision.Nov 23 2020, 2:33 PM
markj created this revision.
This revision was not accepted when it landed; it landed in state Needs Review.Nov 30 2020, 4:19 PM
This revision was automatically updated to reflect the committed changes.