util/oslib-posix: Fix missing unlock in the error path of os_mem_prea…

…lloc()

We're missing an unlock in case installing the signal handler failed.
Fortunately, we barely see this error in real life.

Fixes: a960d66 ("util/oslib-posix: Support concurrent os_mem_prealloc() invocation")
Fixes: CID 1468941
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta@ionos.com>
Cc: Daniel P. Berrangé <berrange@redhat.com>
Cc: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20220111120830.119912-1-david@redhat.com>
Reviewed-by: Pankaj Gupta <pankaj.gupta@ionos.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

util/oslib-posix.c

@@ -683,6 +683,7 @@ void os_mem_prealloc(int fd, char *area, size_t memory, int smp_cpus,
 
         ret = sigaction(SIGBUS, &act, &sigbus_oldact);
         if (ret) {
+            qemu_mutex_unlock(&sigbus_mutex);
             error_setg_errno(errp, errno,
                 "os_mem_prealloc: failed to install signal handler");
             return;