From 38a4a5349c8f54a8d835675d395365d11628afac Mon Sep 17 00:00:00 2001 From: Teodor Sigaev Date: Fri, 21 Jul 2017 13:31:49 +0300 Subject: [PATCH] Fix double shared memory allocation. SLRU buffer lwlocks are allocated twice by oversight in commit fe702a7b3f9f2bc5bf6d173166d7d55226af82c8 where that locks were moved to separate tranche. The bug doesn't have user-visible effects except small overspending of shared memory. Backpatch to 9.6 where it was introduced. Alexander Korotkov with small editorization by me. --- src/backend/access/transam/slru.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/src/backend/access/transam/slru.c b/src/backend/access/transam/slru.c index bbae5847f2..ee111ca539 100644 --- a/src/backend/access/transam/slru.c +++ b/src/backend/access/transam/slru.c @@ -204,15 +204,16 @@ SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns, shared->page_lru_count = (int *) (ptr + offset); offset += MAXALIGN(nslots * sizeof(int)); + /* Initialize LWLocks */ + shared->buffer_locks = (LWLockPadded *) (ptr + offset); + offset += MAXALIGN(nslots * sizeof(LWLockPadded)); + if (nlsns > 0) { shared->group_lsn = (XLogRecPtr *) (ptr + offset); offset += MAXALIGN(nslots * nlsns * sizeof(XLogRecPtr)); } - /* Initialize LWLocks */ - shared->buffer_locks = (LWLockPadded *) ShmemAlloc(sizeof(LWLockPadded) * nslots); - Assert(strlen(name) + 1 < SLRU_MAX_NAME_LENGTH); strlcpy(shared->lwlock_tranche_name, name, SLRU_MAX_NAME_LENGTH); shared->lwlock_tranche_id = tranche_id; @@ -232,6 +233,9 @@ SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns, shared->page_lru_count[slotno] = 0; ptr += BLCKSZ; } + + /* Should fit to estimated shmem size */ + Assert(ptr - (char *) shared <= SimpleLruShmemSize(nslots, nlsns)); } else Assert(found);