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Wed, 16 Apr 2025 19:31:23 -0400 X-MC-Unique: -fG8ywgYPrCLDmfO-Wd0hA-1 X-Mimecast-MFC-AGG-ID: -fG8ywgYPrCLDmfO-Wd0hA_1744846280 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 50AC51800876; Wed, 16 Apr 2025 23:31:20 +0000 (UTC) Received: from fedora (unknown [10.72.116.82]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id B71C130001A1; Wed, 16 Apr 2025 23:31:16 +0000 (UTC) Date: Thu, 17 Apr 2025 07:31:11 +0800 From: Ming Lei To: Uday Shankar Cc: Jens Axboe , linux-block@vger.kernel.org, Caleb Sander Mateos Subject: Re: [PATCH V2 4/8] ublk: move device reset into ublk_ch_release() Message-ID: References: <20250416035444.99569-1-ming.lei@redhat.com> <20250416035444.99569-5-ming.lei@redhat.com> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 On Wed, Apr 16, 2025 at 01:02:42PM -0600, Uday Shankar wrote: > On Wed, Apr 16, 2025 at 11:54:38AM +0800, Ming Lei wrote: > > ublk_ch_release() is called after ublk char device is closed, when all > > uring_cmd are done, so it is perfect fine to move ublk device reset to > > ublk_ch_release() from ublk_ctrl_start_recovery(). > > > > This way can avoid to grab the exiting daemon task_struct too long. > > > > However, reset of the following ublk IO flags has to be moved until ublk > > io_uring queues are ready: > > > > - ubq->canceling > > > > For requeuing IO in case of ublk_nosrv_dev_should_queue_io() before device > > is recovered > > > > - ubq->fail_io > > > > For failing IO in case of UBLK_F_USER_RECOVERY_FAIL_IO before device is > > recovered > > > > - ublk_io->flags > > > > For preventing using io->cmd > > > > With this way, recovery is simplified a lot. > > > > Signed-off-by: Ming Lei > > --- > > drivers/block/ublk_drv.c | 121 +++++++++++++++++++++++---------------- > > 1 file changed, 72 insertions(+), 49 deletions(-) > > > > diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c > > index a479969fd77e..1fe39cf85b2f 100644 > > --- a/drivers/block/ublk_drv.c > > +++ b/drivers/block/ublk_drv.c > > @@ -1074,7 +1074,7 @@ static inline struct ublk_uring_cmd_pdu *ublk_get_uring_cmd_pdu( > > > > static inline bool ubq_daemon_is_dying(struct ublk_queue *ubq) > > { > > - return ubq->ubq_daemon->flags & PF_EXITING; > > + return !ubq->ubq_daemon || ubq->ubq_daemon->flags & PF_EXITING; > > } > > > > /* todo: handle partial completion */ > > @@ -1470,6 +1470,37 @@ static const struct blk_mq_ops ublk_mq_ops = { > > .timeout = ublk_timeout, > > }; > > > > +static void ublk_queue_reinit(struct ublk_device *ub, struct ublk_queue *ubq) > > +{ > > + int i; > > + > > + /* All old ioucmds have to be completed */ > > + ubq->nr_io_ready = 0; > > + > > + /* > > + * old daemon is PF_EXITING, put it now > > + * > > + * It could be NULL in case of closing one quisced device. > > + */ > > + if (ubq->ubq_daemon) > > + put_task_struct(ubq->ubq_daemon); > > + /* We have to reset it to NULL, otherwise ub won't accept new FETCH_REQ */ > > + ubq->ubq_daemon = NULL; > > + ubq->timeout = false; > > + > > + for (i = 0; i < ubq->q_depth; i++) { > > + struct ublk_io *io = &ubq->ios[i]; > > + > > + /* > > + * UBLK_IO_FLAG_CANCELED is kept for avoiding to touch > > + * io->cmd > > + */ > > + io->flags &= UBLK_IO_FLAG_CANCELED; > > + io->cmd = NULL; > > + io->addr = 0; > > + } > > +} > > + > > static int ublk_ch_open(struct inode *inode, struct file *filp) > > { > > struct ublk_device *ub = container_of(inode->i_cdev, > > @@ -1481,10 +1512,26 @@ static int ublk_ch_open(struct inode *inode, struct file *filp) > > return 0; > > } > > > > +static void ublk_reset_ch_dev(struct ublk_device *ub) > > +{ > > + int i; > > + > > + for (i = 0; i < ub->dev_info.nr_hw_queues; i++) > > + ublk_queue_reinit(ub, ublk_get_queue(ub, i)); > > + > > + /* set to NULL, otherwise new ubq_daemon cannot mmap the io_cmd_buf */ > > + ub->mm = NULL; > > + ub->nr_queues_ready = 0; > > + ub->nr_privileged_daemon = 0; > > +} > > + > > static int ublk_ch_release(struct inode *inode, struct file *filp) > > { > > struct ublk_device *ub = filp->private_data; > > > > + /* all uring_cmd has been done now, reset device & ubq */ > > + ublk_reset_ch_dev(ub); > > Can we take the ub->mutex here? I can't see a concrete data race but I > feel there is lots of potential for one since the device still may be > concurrently accessed via ctrl commands. Actually it isn't needed: - only the two RECOVERY commands may touch this data, but START_USER_RECOVERY waits until close is done. - for other commands, this data won't be touched, and just the state update need to be protected by ub->mutex, which is always true. ublk_cancel_dev() is one exception, but ubq->cancel_lock provides the protection. thanks, Ming