linux-kernel - fix block device size update serialization

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Message-Id: <20200821085600.2395666-1-hch@lst.de>
Date:   Fri, 21 Aug 2020 10:55:58 +0200
From:   Christoph Hellwig <hch@....de>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Justin Sanders <justin@...aid.com>,
        Josef Bacik <josef@...icpanda.com>,
        Xianting Tian <xianting_tian@....com>,
        linux-block@...r.kernel.org, dm-devel@...hat.com,
        Stefan Haberland <sth@...ux.ibm.com>,
        Jan Hoeppner <hoeppner@...ux.ibm.com>,
        linux-kernel@...r.kernel.org, nbd@...er.debian.org,
        linux-nvme@...ts.infradead.org, linux-s390@...r.kernel.org
Subject: fix block device size update serialization

Hi Jens,

this series fixes how we update i_size for the block device inodes (and
thus the block device).  Different helpers use two different locks
(bd_mutex and i_rwsem) to protect the update, and it appears device
mapper uses yet another internal lock.  A lot of the drivers do the
update handcrafted in often crufty ways.  And in addition to that mess
it turns out that the "main" lock, bd_mutex is pretty dead lock prone
vs other spots in the block layer that acquire it during revalidation
operations, as reported by Xianting.

Fix all that by adding a dedicated spinlock just for the size updates.