CVS commit: src/sys/kern

["Taylor R Campbell" <riastradh%netbsd.org@localhost>]

Module Name:    src
Committed By:   riastradh
Date:           Thu Feb 23 03:01:22 UTC 2023

Modified Files:
        src/sys/kern: subr_pcq.c

Log Message:
pcq(9): Fix consume operation in pcq_peek/get.

These use atomic_load_consume to match the atomic_store_release in
pcq_put for pcq->pcq_items[c].

Reading the snapshot of pcq->pcq_pc need not be ordered:

- The consumer side (pcq_peek/get) is serialized by the API contract
  (single-consumer, multi-producer), so no ordering is necessary.

- The producer side updates pcq->pcq_pc first; if the consumer side
  sees that before the producer side has stored pcq->pcq_items[c],
  there's no problem -- it's as if the consumer had happened just a
  moment earlier and the producer hadn't entered pcq_put yet.

However, it should be an atomic load, not a plain load.  So use
atomic_load_relaxed, if for no other reason than to pacify thread
sanitizers.

XXX pullup-9
XXX pullup-10


To generate a diff of this commit:
cvs rdiff -u -r1.14 -r1.15 src/sys/kern/subr_pcq.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.