dm cache: fix race affecting dirty block count

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commit 44fa816bb7 upstream.

nr_dirty is updated without locking, causing it to drift so that it is
non-zero (either a small positive integer, or a very large one when an
underflow occurs) even when there are no actual dirty blocks.  This was
due to a race between the workqueue and map function accessing nr_dirty
in parallel without proper protection.

People were seeing under runs due to a race on increment/decrement of
nr_dirty, see: https://lkml.org/lkml/2014/6/3/648

Fix this by using an atomic_t for nr_dirty.

Reported-by: roma1390@gmail.com
Signed-off-by: Anssi Hannula <anssi.hannula@iki.fi>
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

...

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Anssi Hannula 2014-08-01 11:55:47 -04:00 • committed by Greg Kroah-Hartman

parent 549e73fd84

commit 649bf3fdd2

1 changed files with 6 additions and 7 deletions

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drivers/md/dm-cache-target.c

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