linux-kernel - [PATCH 0/4] Fix a crash when block device is read and block size is changed at the same time

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Date:	Fri, 31 Aug 2012 14:40:26 -0400 (EDT)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
cc:	Jens Axboe <axboe@...nel.dk>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Jan Kara <jack@...e.cz>, dm-devel@...hat.com,
	linux-kernel@...r.kernel.org, Jeff Moyer <jmoyer@...hat.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	kosaki.motohiro@...fujitsu.com, linux-fsdevel@...r.kernel.org,
	lwoodman@...hat.com, "Alasdair G. Kergon" <agk@...hat.com>
Subject: [PATCH 0/4] Fix a crash when block device is read and block size is
 changed at the same time

Hi

This is a series of patches to prevent a crash when when someone is 
reading block device and block size is changed simultaneously. (the crash 
is already happening in the production environment)

The first patch adds a rw-lock to struct block_device, but doesn't use the 
lock anywhere. The reason why I submit this as a separate patch is that on 
my computer adding an unused field to this structure affects performance 
much more than any locking changes.

The second patch uses the rw-lock. The lock is locked for read when doing 
I/O on the block device and it is locked for write when changing block 
size.

The third patch converts the rw-lock to a percpu rw-lock for better 
performance, to avoid cache line bouncing.

The fourth patch is an alternate percpu rw-lock implementation using RCU 
by Eric Dumazet. It avoids any atomic instruction in the hot path.

Mikulas
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