CVS commit: src/sys

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

Module Name:    src
Committed By:   riastradh
Date:           Sun Aug 23 17:49:11 UTC 2026

Modified Files:
        src/sys/kern: subr_pool.c
        src/sys/sys: pool.h

Log Message:
pool(9): Nix useless PR_GROWINGNOWAIT bit.

This was introduced back in 2017 as an attempt to avoid spurious
failure in concurrent PR_NOWAIT allocations, while still serializing
calls to the pool's back end allocator to avoid fragmentation:

https://mail-index.NetBSD.org/source-changes/2017/12/16/msg090490.html

However, this probably doesn't work very well when one pool_get call
in the middle of pool_grow is _interrupted by_ another one (in an
interrupt handler) -- the busy wait will turn into a deadlock:

https://mail-index.NetBSD.org/current-users/2017/12/29/msg033000.html

So the logic was changed to keep holding the lock across the backing
allocator in PR_NOWAIT allocations -- this way, calls to the pool's
back end allocator are still serialized, but we at least avoid
holding the lock _while sleeping_ in the back end allocator:

https://mail-index.NetBSD.org/current-users/2017/12/29/msg033001.html

But with that change, the PR_GROWINGNOWAIT bit no longer served any
purpose, because it only stays set _while the lock is held_ so no
other threads can observe it anyway.

Cleanup prompted by:

PR kern/59411: deadlock on mbuf pool


To generate a diff of this commit:
cvs rdiff -u -r1.297 -r1.298 src/sys/kern/subr_pool.c
cvs rdiff -u -r1.96 -r1.97 src/sys/sys/pool.h

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