Re: [PATCH] virtio-blk: don't keep queue frozen during system suspend

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Tue, Nov 12, 2024 at 08:58:21PM +0800, Ming Lei wrote:
> Commit 4ce6e2db00de ("virtio-blk: Ensure no requests in virtqueues before
> deleting vqs.") replaces queue quiesce with queue freeze in virtio-blk's
> PM callbacks. And the motivation is to drain inflight IOs before suspending.
> 
> block layer's queue freeze looks very handy, but it is also easy to cause
> deadlock, such as, any attempt to call into bio_queue_enter() may run into
> deadlock if the queue is frozen in current context. There are all kinds
> of ->suspend() called in suspend context, so keeping queue frozen in the
> whole suspend context isn't one good idea. And Marek reported lockdep
> warning[1] caused by virtio-blk's freeze queue in virtblk_freeze().
> 
> [1] https://lore.kernel.org/linux-block/ca16370e-d646-4eee-b9cc-87277c89c43c@samsung.com/
> 
> Given the motivation is to drain in-flight IOs, it can be done by calling
> freeze & unfreeze, meantime restore to previous behavior by keeping queue
> quiesced during suspend.
> 
> Cc: Yi Sun <yi.sun@unisoc.com>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Jason Wang <jasowang@redhat.com>
> Cc: Stefan Hajnoczi <stefanha@redhat.com>
> Cc: virtualization@lists.linux.dev
> Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
>  drivers/block/virtio_blk.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)

Acked-by: Stefan Hajnoczi <stefanha@redhat.com>

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