From 8d724382d8a82c007798d735acdeb5ba05911be9 Mon Sep 17 00:00:00 2001 From: Amit Kapila Date: Fri, 1 Feb 2019 10:40:12 +0530 Subject: [PATCH] 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 3da0b49..5839c16 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); -- 1.8.3.1