Thank you, Stefan, I tested this one as well and it boots now and seems to behave correctly under the load as well.
Regards,
Lukáš
Tested-by: Lukas Doktor <ldok...@redhat.com>
Dne 12. 07. 23 v 21:16 Stefan Hajnoczi napsal(a):
> blk_io_plug_call() is invoked outside a blk_io_plug()/blk_io_unplug()
> section while opening the NVMe drive from:
>
> nvme_file_open() ->
> nvme_init() ->
> nvme_identify() ->
> nvme_admin_cmd_sync() ->
> nvme_submit_command() ->
> blk_io_plug_call()
>
> blk_io_plug_call() immediately invokes the given callback when the
> current thread is not plugged, as is the case during nvme_file_open().
>
> Unfortunately, nvme_submit_command() calls blk_io_plug_call() with
> q->lock still held:
>
> ...
> q->sq.tail = (q->sq.tail + 1) % NVME_QUEUE_SIZE;
> q->need_kick++;
> blk_io_plug_call(nvme_unplug_fn, q);
> qemu_mutex_unlock(&q->lock);
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> nvme_unplug_fn() deadlocks trying to acquire q->lock because the lock is
> already acquired by the same thread. The symptom is that QEMU hangs
> during startup while opening the NVMe drive.
>
> Fix this by moving the blk_io_plug_call() outside q->lock. This is safe
> because no other thread runs code related to this queue and
> blk_io_plug_call()'s internal state is immune to thread safety issues
> since it is thread-local.
>
> Reported-by: Lukáš Doktor <ldok...@redhat.com>
> Fixes: f2e590002bd6 ("block/nvme: convert to blk_io_plug_call() API")
> Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
> ---
> block/nvme.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/block/nvme.c b/block/nvme.c
> index 7ca85bc44a..b6e95f0b7e 100644
> --- a/block/nvme.c
> +++ b/block/nvme.c
> @@ -501,8 +501,9 @@ static void nvme_submit_command(NVMeQueuePair *q,
> NVMeRequest *req,
> q->sq.tail * NVME_SQ_ENTRY_BYTES, cmd, sizeof(*cmd));
> q->sq.tail = (q->sq.tail + 1) % NVME_QUEUE_SIZE;
> q->need_kick++;
> + qemu_mutex_unlock(&q->lock);
> +
> blk_io_plug_call(nvme_unplug_fn, q);
> - qemu_mutex_unlock(&q->lock);
> }
>
> static void nvme_admin_cmd_sync_cb(void *opaque, int ret)
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