diff options
| author | Andres Freund <andres@anarazel.de> | 2025-11-24 17:37:09 -0500 |
|---|---|---|
| committer | Andres Freund <andres@anarazel.de> | 2025-11-24 18:10:48 -0500 |
| commit | 81f773895321ac69d3d71fe9d203e09d072f9c36 (patch) | |
| tree | 3e8e98efe0d141533bf884e67feb473e8b6b8b31 /src | |
| parent | f81bf78ce12b9fd3e50eb00dd875440007262ec4 (diff) | |
lwlock: Fix, currently harmless, bug in LWLockWakeup()
Accidentally the code in LWLockWakeup() checked the list of to-be-woken up
processes to see if LW_FLAG_HAS_WAITERS should be unset. That means that
HAS_WAITERS would not get unset immediately, but only during the next,
unnecessary, call to LWLockWakeup().
Luckily, as the code stands, this is just a small efficiency issue.
However, if there were (as in a patch of mine) a case in which LWLockWakeup()
would not find any backend to wake, despite the wait list not being empty,
we'd wrongly unset LW_FLAG_HAS_WAITERS, leading to potentially hanging.
While the consequences in the backbranches are limited, the code as-is
confusing, and it is possible that there are workloads where the additional
wait list lock acquisitions hurt, therefore backpatch.
Discussion: https://postgr.es/m/fvfmkr5kk4nyex56ejgxj3uzi63isfxovp2biecb4bspbjrze7@az2pljabhnff
Backpatch-through: 14
Diffstat (limited to 'src')
| -rw-r--r-- | src/backend/storage/lmgr/lwlock.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c index b017880f5e4..255cfa8fa95 100644 --- a/src/backend/storage/lmgr/lwlock.c +++ b/src/backend/storage/lmgr/lwlock.c @@ -998,7 +998,7 @@ LWLockWakeup(LWLock *lock) else desired_state &= ~LW_FLAG_RELEASE_OK; - if (proclist_is_empty(&wakeup)) + if (proclist_is_empty(&lock->waiters)) desired_state &= ~LW_FLAG_HAS_WAITERS; desired_state &= ~LW_FLAG_LOCKED; /* release lock */ |