tree 786cdf119ce33641438cd841deb0c480dd92f900
parent a6d8113a986c66aeb379a26b6e0062488b3e59e1
author Dan Williams <dan.j.williams@intel.com> 1212731154 -0700
committer Linus Torvalds <torvalds@linux-foundation.org> 1212776948 -0700

md: do not compute parity unless it is on a failed drive

If a block is computed (rather than read) then a check/repair operation
may be lead to believe that the data on disk is correct, when infact it
isn't.  So only compute blocks for failed devices.

This issue has been around since at least 2.6.12, but has become harder to
hit in recent kernels since most reads bypass the cache.

echo repair > /sys/block/mdN/md/sync_action will set the parity blocks to the
correct state.

Cc: <stable@kernel.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>