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Move memory barrier in UnlockBufHdr to before releasing the lock.

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This bug appears to have been introduced late in the development of
48354581a4 ("Allow Pin/UnpinBuffer to operate in a lockfree
manner.").

Found while debugging a bug which turned out to be independent of the
commit mentioned above.

Backpatch: -
This commit is contained in:
Andres Freund 2016-05-30 15:35:53 -07:00
parent 975ad4e602
commit 87a3023c60
1 changed files with 1 additions and 1 deletions
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2
src/include/storage/buf_internals.h
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@ -242,8 +242,8 @@ extern PGDLLIMPORT LWLockMinimallyPadded *BufferIOLWLockArray;
extern uint32 LockBufHdr(BufferDesc *desc);
#define UnlockBufHdr(desc, s) \
do { \
pg_atomic_write_u32(&(desc)->state, (s) & (~BM_LOCKED)); \
pg_write_barrier(); \
pg_atomic_write_u32(&(desc)->state, (s) & (~BM_LOCKED)); \
} while (0)