From 0f928a85ecd509b165bfb9acd71b18c40063a7a0 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Mon, 5 May 2014 14:43:39 -0400 Subject: [PATCH] Fix possible cache invalidation failure in ReceiveSharedInvalidMessages. Commit fad153ec45299bd4d4f29dec8d9e04e2f1c08148 modified sinval.c to reduce the number of calls into sinvaladt.c (which require taking a shared lock) by keeping a local buffer of collected-but-not-yet-processed messages. However, if processing of the last message in a batch resulted in a recursive call to ReceiveSharedInvalidMessages, we could overwrite that message with a new one while the outer invalidation function was still working on it. This would be likely to lead to invalidation of the wrong cache entry, allowing subsequent processing to use stale cache data. The fix is just to make a local copy of each message while we're processing it. Spotted by Andres Freund. Back-patch to 8.4 where the bug was introduced. --- src/backend/storage/ipc/sinval.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/src/backend/storage/ipc/sinval.c b/src/backend/storage/ipc/sinval.c index edd0d73a46..264f700207 100644 --- a/src/backend/storage/ipc/sinval.c +++ b/src/backend/storage/ipc/sinval.c @@ -91,10 +91,10 @@ ReceiveSharedInvalidMessages( /* Deal with any messages still pending from an outer recursion */ while (nextmsg < nummsgs) { - SharedInvalidationMessage *msg = &messages[nextmsg++]; + SharedInvalidationMessage msg = messages[nextmsg++]; SharedInvalidMessageCounter++; - invalFunction(msg); + invalFunction(&msg); } do @@ -121,10 +121,10 @@ ReceiveSharedInvalidMessages( while (nextmsg < nummsgs) { - SharedInvalidationMessage *msg = &messages[nextmsg++]; + SharedInvalidationMessage msg = messages[nextmsg++]; SharedInvalidMessageCounter++; - invalFunction(msg); + invalFunction(&msg); } /* -- 2.40.0