nvme: Kick and check completions in BDS context

nvme_process_completion() must run in the main BDS context, so schedule
a BH for requests that aren’t there.

The context in which we kick does not matter, but let’s just keep kick
and process_completion together for simplicity’s sake.

(For what it’s worth, a quick fio bandwidth test indicates that on my
test hardware, if anything, this may be a bit better than kicking
immediately before scheduling a pure nvme_process_completion() BH.  But
I wouldn’t take more from those results than that it doesn’t really seem
to matter either way.)

Cc: qemu-stable@nongnu.org
Signed-off-by: Hanna Czenczek <hreitz@redhat.com>
Message-ID: <20251110154854.151484-8-hreitz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/nvme.c

@@ -481,7 +481,7 @@ static void nvme_trace_command(const NvmeCmd *cmd)
     }
 }
 
-static void nvme_deferred_fn(void *opaque)
+static void nvme_kick_and_check_completions(void *opaque)
 {
     NVMeQueuePair *q = opaque;
 
@@ -490,6 +490,18 @@ static void nvme_deferred_fn(void *opaque)
     nvme_process_completion(q);
 }
 
+static void nvme_deferred_fn(void *opaque)
+{
+    NVMeQueuePair *q = opaque;
+
+    if (qemu_get_current_aio_context() == q->s->aio_context) {
+        nvme_kick_and_check_completions(q);
+    } else {
+        aio_bh_schedule_oneshot(q->s->aio_context,
+                                nvme_kick_and_check_completions, q);
+    }
+}
+
 static void nvme_submit_command(NVMeQueuePair *q, NVMeRequest *req,
                                 NvmeCmd *cmd, BlockCompletionFunc cb,
                                 void *opaque)