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Fix RBM_ZERO_AND_LOCK mode to not acquire lock on local buffers.

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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.
This commit is contained in:
Heikki Linnakangas 2015-05-13 09:44:43 +03:00
parent 46f9acd3ef
commit 1a99d392c1
1 changed files with 2 additions and 1 deletions
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3
src/backend/storage/buffer/bufmgr.c
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@ -511,7 +511,8 @@ 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)