block/nvme: don't access CQE after moving cq.head
Do not access a CQE after incrementing q->cq.head and releasing q->lock.
It is unlikely that this causes problems in practice but it's a latent
bug.
The reason why it should be safe at the moment is that completion
processing is not re-entrant and the CQ doorbell isn't written until the
end of nvme_process_completion().
Make this change now because QEMU expects completion processing to be
re-entrant and later patches will do that.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Sergio Lopez <slp@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20200617132201.1832152-4-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/block/nvme.c b/block/nvme.c
index d567ece..3448938 100644
--- a/block/nvme.c
+++ b/block/nvme.c
@@ -321,11 +321,14 @@
q->busy = true;
assert(q->inflight >= 0);
while (q->inflight) {
+ int ret;
int16_t cid;
+
c = (NvmeCqe *)&q->cq.queue[q->cq.head * NVME_CQ_ENTRY_BYTES];
if ((le16_to_cpu(c->status) & 0x1) == q->cq_phase) {
break;
}
+ ret = nvme_translate_error(c);
q->cq.head = (q->cq.head + 1) % NVME_QUEUE_SIZE;
if (!q->cq.head) {
q->cq_phase = !q->cq_phase;
@@ -344,7 +347,7 @@
preq->busy = false;
preq->cb = preq->opaque = NULL;
qemu_mutex_unlock(&q->lock);
- req.cb(req.opaque, nvme_translate_error(c));
+ req.cb(req.opaque, ret);
qemu_mutex_lock(&q->lock);
q->inflight--;
progress = true;
