Module Name: src
Committed By: riastradh
Date: Fri Feb 11 21:40:59 UTC 2022
Modified Files:
src/lib/libpthread: pthread_rwlock.c
Log Message:
libpthread: Fix membars around rwlocks.
1. After loading self->pt_rwlocked, membar_enter() must not be
conditional on PTHREAD__ATOMIC_IS_MEMBAR because there is no
atomic r/m/w operation here which could imply the acquire barrier.
(This should maybe just be a load-acquire operation, but we don't
have atomic_load_acquire in userland at the moment -- TBD.)
2. Before storing thread->pt_rwlocked, must issue membar_exit() so
that this is a store-release operation -- except if we had just
done an atomic r/m/w and PTHREAD__ATOMIC_IS_MEMBAR is set, in
which case it can be elided.
The second membar_exit() added here might be safely hoisted out of
the loop but I'm not sure -- needs more analysis to prove that
would be safe.
To generate a diff of this commit:
cvs rdiff -u -r1.42 -r1.43 src/lib/libpthread/pthread_rwlock.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
