postgres.git / summary / log / commit / refs

commit    0b8bdb3c3ec092f18813d5b6fc738d7ec450289b
Author:   Amit Kapila <akapila@postgresql.org>
Date:     Sat Feb 02 10:17:00 2019 +0000

    Avoid possible deadlock while locking multiple heap pages.
    
    To avoid deadlock, backend acquires a lock on heap pages in block
    number order.  In certain cases, lock on heap pages is dropped and
    reacquired.  In this case, the locks are dropped for reading in
    corresponding VM page/s. The issue is we re-acquire locks in bufferId
    order whereas the intention was to acquire in blockid order.
    
    This commit ensures that we will always acquire locks on heap pages in
    blockid order.
    
    Reported-by: Nishant Fnu
    Author: Nishant Fnu
    Reviewed-by: Amit Kapila and Robert Haas
    Backpatch-through: 9.4
    Discussion: https://postgr.es/m/5883C831-2ED1-47C8-BFAC-2D5BAE5A8CAE@amazon.com


 src/backend/access/heap/hio.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/backend/access/heap/hio.c b/src/backend/access/heap/hio.c
index 3da0b49ccc4..5839c168e6c 100644
--- a/src/backend/access/heap/hio.c
+++ b/src/backend/access/heap/hio.c
@@ -115,8 +115,8 @@ ReadBufferBI(Relation relation, BlockNumber targetBlock,
  * visibility map page, if we haven't already got one.
  *
  * buffer2 may be InvalidBuffer, if only one buffer is involved.  buffer1
- * must not be InvalidBuffer.  If both buffers are specified, buffer1 must
- * be less than buffer2.
+ * must not be InvalidBuffer.  If both buffers are specified, block1 must
+ * be less than block2.
  */
 static void
 GetVisibilityMapPins(Relation relation, Buffer buffer1, Buffer buffer2,
@@ -127,7 +127,7 @@ GetVisibilityMapPins(Relation relation, Buffer buffer1, Buffer buffer2,
 	bool		need_to_pin_buffer2;
 
 	Assert(BufferIsValid(buffer1));
-	Assert(buffer2 == InvalidBuffer || buffer1 <= buffer2);
+	Assert(buffer2 == InvalidBuffer || block1 <= block2);
 
 	while (1)
 	{
@@ -465,7 +465,7 @@ loop:
 		 * done a bit of extra work for no gain, but there's no real harm
 		 * done.
 		 */
-		if (otherBuffer == InvalidBuffer || buffer <= otherBuffer)
+		if (otherBuffer == InvalidBuffer || targetBlock <= otherBlock)
 			GetVisibilityMapPins(relation, buffer, otherBuffer,
 								 targetBlock, otherBlock, vmbuffer,
 								 vmbuffer_other);


[parent: 3e938a83b2ee]