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Date:   Fri, 16 Jun 2023 09:27:21 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Ming Lei <ming.lei@redhat.com>
Cc:     Christoph Hellwig <hch@lst.de>, Keith Busch <kbusch@kernel.org>,
        Jens Axboe <axboe@kernel.dk>, Sagi Grimberg <sagi@grimberg.me>,
        linux-nvme@lists.infradead.org, Yi Zhang <yi.zhang@redhat.com>,
        linux-block@vger.kernel.org, Chunguang Xu <brookxu.cn@gmail.com>
Subject: Re: [PATCH 1/4] blk-mq: add API of blk_mq_unfreeze_queue_force
Message-ID: <20230616072721.GA30186@lst.de>
References: <20230615143236.297456-1-ming.lei@redhat.com> <20230615143236.297456-2-ming.lei@redhat.com> <ZIsrSyEqWMw8/ikq@kbusch-mbp.dhcp.thefacebook.com> <ZIsxt7Q2nmiLNTX2@ovpn-8-16.pek2.redhat.com> <20230616054800.GA28499@lst.de> <ZIwNRu1zodp61PEO@ovpn-8-18.pek2.redhat.com>
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On Fri, Jun 16, 2023 at 03:20:38PM +0800, Ming Lei wrote:
> > > > Shouldn't those writebacks be unblocked by the existing check in
> > > > bio_queue_enter, test_bit(GD_DEAD, &disk->state))? Or are we missing a
> > > > disk state update or wakeup on this condition?
> > > 
> > > GD_DEAD is only set if the device is really dead, then all pending IO
> > > will be failed.
> > 
> > del_gendisk also sets GD_DEAD early on.
> 
> No.
> 
> The hang happens in fsync_bdev() of del_gendisk(), and there are IOs pending on
> bio_queue_enter().

What is the workload here?  If del_gendisk is called to remove a disk
that is in perfectly fine state and can do I/O, fsync_bdev should write
back data, which is what is exists for.  If the disk is dead, we should
have called blk_mark_disk_dead before.