postgres.git / summary / log / commit / refs

commit    7e1fb4c59e4ac86de2640d0f3453fde270ec1ff8
Author:   Teodor Sigaev <teodor@sigaev.ru>
Date:     Fri Jul 21 10:31:20 2017 +0000

    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 93ec653dd60..d037c369a72 100644
--- a/src/backend/access/transam/slru.c
+++ b/src/backend/access/transam/slru.c
@@ -205,15 +205,16 @@ 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;
@@ -230,6 +231,9 @@ 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);


[parent: 68f785fd522b]