Re: [PATCH] ublk: fix AB-BA lockdep warning

From: Ming Lei <ming.lei@redhat.com>
To: Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Cc: Jens Axboe <axboe@kernel.dk>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	Ziyang Zhang <ZiyangZhang@linux.alibaba.com>
Subject: Re: [PATCH] ublk: fix AB-BA lockdep warning
Date: Thu, 18 May 2023 10:59:10 +0800	[thread overview]
Message-ID: <ZGWUfv+g6EOw/pI2@ovpn-8-16.pek2.redhat.com> (raw)
In-Reply-To: <a57cn4zqgxm5hds2ekgg2y5jbfd4bgwoujimit7enm6eh5wo56@hftyn26mv3aq>

On Thu, May 18, 2023 at 02:01:17AM +0000, Shinichiro Kawasaki wrote:
> On May 17, 2023 / 21:34, Ming Lei wrote:
> > When handling UBLK_IO_FETCH_REQ, ctx->uring_lock is grabbed first, then
> > ub->mutex is acquired.
> > 
> > When handling UBLK_CMD_STOP_DEV or UBLK_CMD_DEL_DEV, ub->mutex is
> > grabbed first, then calling io_uring_cmd_done() for canceling uring
> > command, in which ctx->uring_lock may be required.
> > 
> > Real deadlock only happens when all the above commands are issued from
> > same uring context, and in reality different uring contexts are often used
> > for handing control command and IO command.
> > 
> > Fix the issue by using io_uring_cmd_complete_in_task() to cancel command
> > in ublk_cancel_dev(ublk_cancel_queue).
> > 
> > Reported-by: Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>
> > Closes: https://lore.kernel.org/linux-block/becol2g7sawl4rsjq2dztsbc7mqypfqko6wzsyoyazqydoasml@rcxarzwidrhk
> > Cc: Ziyang Zhang <ZiyangZhang@linux.alibaba.com>
> > Signed-off-by: Ming Lei <ming.lei@redhat.com>
> 
> Using Ziyang's new blktests test cases, I confirmed this patch avoids the
> failure I reported. Thanks.
> 
> Tested-by: Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>

Shinichiro, Thanks for the test!

-- 
Ming