Re: [libvirt] [PATCH] add an assert, to avoid a false-positive NULL-deref warning from clang

1 Mar 2010


      According to Jim Meyering on 3/1/2010 10:13 AM:
...
Here's a case in which using an assertion appears to be the only
way to tell clang that "client" really is non-NULL at that point.
I'm sure clang's analyzers will eventually improve, and hence avoid
this sort of false positive, so have marked this with a FIXME comment,
to help ensure we eventually remove this otherwise unnecessary assertion.
Thanks for the extra context; it makes in-line review a breeze.
...
@@ -1504,34 +1505,38 @@ static void *qemudWorker(void *data)
         virMutexLock(&server->lock);
         while (((client = qemudPendingJob(server)) == NULL) &&
                !worker->quitRequest) {
             if (virCondWait(&server->job, &server->lock) < 0) {
                 virMutexUnlock(&server->lock);
                 return NULL;
             }
         }
Indeed, the only way client can be NULL at this point is if
worker->quitRequest is true...
...
if (worker->quitRequest) {
             if (client)
                 virMutexUnlock(&client->lock);
             virMutexUnlock(&server->lock);
             return NULL;
         }
But that means we exit here.
...
worker->processingCall = 1;
         virMutexUnlock(&server->lock);
+        /* Tell clang we know what we're doing.
+           FIXME: remove when clang improves.  */
+        assert (client);
So this assertion is valid.  ACK, if assert() is okay.

On the other hand, perhaps a more invasive rewrite would also work while
also avoiding assert(), by hoisting the worker->quitRequest into the while
loop, something like:

     while ((client = qemudPendingJob(server)) == NULL) {
         if (worker->quitRequest
             || virCondWait(&server->job, &server->lock) < 0) {
             virMutexUnlock(&server->lock);
             return NULL;
         }
     }
     if (worker->quitRequest) {
         virMutexUnlock(&client->lock);
         virMutexUnlock(&server->lock);
         return NULL;
     }

Should I write that into patch format?

-- 
Eric Blake   eblake@redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

    