From: Heikki Linnakangas Date: Wed, 13 May 2015 06:44:43 +0000 (+0300) Subject: Fix RBM_ZERO_AND_LOCK mode to not acquire lock on local buffers. X-Git-Tag: REL9_4_2~21 X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=462a2f1f019fa16087fe2f59e96e339a703923b2;p=postgresql Fix RBM_ZERO_AND_LOCK mode to not acquire lock on local buffers. Commit 81c45081 introduced a new RBM_ZERO_AND_LOCK mode to ReadBuffer, which takes a lock on the buffer before zeroing it. However, you cannot take a lock on a local buffer, and you got a segfault instead. The version of that patch committed to master included a check for !isLocalBuf, and therefore didn't crash, but oddly I missed that in the back-patched versions. This patch adds that check to the back-branches too. RBM_ZERO_AND_LOCK mode is only used during WAL replay, and in hash indexes. WAL replay only deals with shared buffers, so the only way to trigger the bug is with a temporary hash index. Reported by Artem Ignatyev, analysis by Tom Lane. --- diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index 2f753e52db..19ec7eb231 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -515,7 +515,8 @@ ReadBuffer_common(SMgrRelation smgr, char relpersistence, ForkNumber forkNum, * (Note that we cannot use LockBuffer() of LockBufferForCleanup() here, * because they assert that the buffer is already valid.) */ - if (mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK) + if ((mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK) && + !isLocalBuf) LWLockAcquire(bufHdr->content_lock, LW_EXCLUSIVE); if (isLocalBuf)