Mailing List Archive

Author: phk
Date: 2007-08-07 12:27:34 +0200 (Tue, 07 Aug 2007)
New Revision: 1809

Modified:
trunk/varnish-cache/bin/varnishd/cache_backend.c
Log:
Minimize a race when looking up addresses for backends.

The race is not closed however, proper locking needs to be thought out.

An XXX comment documents this for now.



Modified: trunk/varnish-cache/bin/varnishd/cache_backend.c
===================================================================
--- trunk/varnish-cache/bin/varnishd/cache_backend.c 2007-08-07 07:23:10 UTC (rev 1808)
+++ trunk/varnish-cache/bin/varnishd/cache_backend.c 2007-08-07 10:27:34 UTC (rev 1809)
@@ -116,20 +116,20 @@
return (vbc);
}

-/*--------------------------------------------------------------------*/
+/*--------------------------------------------------------------------
+ * XXX: There is a race here, we need to lock the replacement of the
+ * XXX: resolved addresses, or some other thread might try to access
+ * XXX: them while/during/after we changed them.
+ * XXX: preferably, we should make a copy to the vbe while we hold a
+ * XXX: lock anyway.
+ */

static void
vbe_lookup(struct backend *bp)
{
- struct addrinfo *res, hint;
+ struct addrinfo *res, hint, *old;
int error;

- if (bp->addr != NULL) {
- freeaddrinfo(bp->addr);
- bp->addr = NULL;
- bp->last_addr = NULL;
- }
-
memset(&hint, 0, sizeof hint);
hint.ai_family = PF_UNSPEC;
hint.ai_socktype = SOCK_STREAM;
@@ -144,8 +144,11 @@
printf("getaddrinfo: %s\n", gai_strerror(error)); /* XXX */
return;
}
+ old = bp->addr;
bp->last_addr = res;
bp->addr = res;
+ if (old != NULL)
+ freeaddrinfo(old);
}

/*--------------------------------------------------------------------*/