postgres.git / summary / log / commit / refs

commit    4f4ef042fddb9698fe4147ca15d92992206d3fbb
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Mon May 05 18:43:42 2014 +0000

    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 98eb814dc3d..1b82241280f 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);
 		}
 
 		/*


[parent: 693a82dddf96]