Re: [PATCH V2] ublk: fix deadlock when reading partition table

[Jens Axboe <axboe@kernel.dk>]

On 12/12/25 7:34 AM, Ming Lei wrote:
> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> index df9831783a13..38f138f248e6 100644
> --- a/drivers/block/ublk_drv.c
> +++ b/drivers/block/ublk_drv.c
> @@ -1080,12 +1080,20 @@ static inline struct ublk_uring_cmd_pdu *ublk_get_uring_cmd_pdu(
>  	return io_uring_cmd_to_pdu(ioucmd, struct ublk_uring_cmd_pdu);
>  }
>  
> +static void ublk_end_request(struct request *req, blk_status_t error)
> +{
> +	local_bh_disable();
> +	blk_mq_end_request(req, error);
> +	local_bh_enable();
> +}

This is really almost too ugly to live, as a work-around for what just
happens to be in __fput_deferred()... Surely we can come up with
something better here? Heck even a PF_ flag would be better than this,
imho.

> @@ -1117,14 +1125,26 @@ static inline void __ublk_complete_rq(struct request *req, struct ublk_io *io,
>  	if (unlikely(unmapped_bytes < io->res))
>  		io->res = unmapped_bytes;
>  
> -	if (blk_update_request(req, BLK_STS_OK, io->res))
> +	/*
> +	 * Run bio->bi_end_io() from softirq context for preventing this
> +	 * ublk's blkdev_release() from being called on current's task
> +	 * work, see fput() implementation.

But that's not what it does, running it from softirq context. It simply
disables local bottomhalf interrupts to trick __fput_deferred(), it's
not scheduling ->bi_end_io() to run from softirq context itself.

-- 
Jens Axboe