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NeilBrown 8e0e99ba64 md/raid5: disable 'DISCARD' by default due to safety concerns. 
It has come to my attention (thanks Martin) that 'discard_zeroes_data'
is only a hint.  Some devices in some cases don't do what it
says on the label.

The use of DISCARD in RAID5 depends on reads from discarded regions
being predictably zero.  If a write to a previously discarded region
performs a read-modify-write cycle it assumes that the parity block
was consistent with the data blocks.  If all were zero, this would
be the case.  If some are and some aren't this would not be the case.
This could lead to data corruption after a device failure when
data needs to be reconstructed from the parity.

As we cannot trust 'discard_zeroes_data', ignore it by default
and so disallow DISCARD on all raid4/5/6 arrays.

As many devices are trustworthy, and as there are benefits to using
DISCARD, add a module parameter to over-ride this caution and cause
DISCARD to work if discard_zeroes_data is set.

If a site want to enable DISCARD on some arrays but not on others they
should select DISCARD support at the filesystem level, and set the
raid456 module parameter.
    raid456.devices_handle_discard_safely=Y

As this is a data-safety issue, I believe this patch is suitable for
-stable.
DISCARD support for RAID456 was added in 3.7

Cc: Shaohua Li <shli@kernel.org>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: Heinz Mauelshagen <heinzm@redhat.com>
Cc: stable@vger.kernel.org (3.7+)
Acked-by: Martin K. Petersen <martin.petersen@oracle.com>
Acked-by: Mike Snitzer <snitzer@redhat.com>
Fixes: 620125f2bf
Signed-off-by: NeilBrown <neilb@suse.de>
 		2014-10-02 13:45:00 +10:00
..
bcache bcache: Drop unneeded blk_sync_queue() calls 2014-08-04 15:23:04 -07:00
persistent-data dm transaction manager: fix corruption due to non-atomic transaction commit 2014-03-27 16:56:23 -04:00
Kconfig dm: add era target 2014-03-27 16:56:23 -04:00
Makefile dm: add era target 2014-03-27 16:56:23 -04:00
bitmap.c md/bitmap: remove confusing code from filemap_get_page. 2014-05-29 16:59:47 +10:00
bitmap.h kernfs: s/sysfs_dirent/kernfs_node/ and rename its friends accordingly 2013-12-11 15:28:36 -08:00
dm-bio-prison.c dm bio prison: implement per bucket locking in the dm_bio_prison hash table 2014-06-11 16:48:54 -04:00
dm-bio-prison.h dm thin: return ENOSPC instead of EIO when error_if_no_space enabled 2014-06-03 13:44:08 -04:00
dm-bio-record.h dm: Refactor for new bio cloning/splitting 2013-11-23 22:33:55 -08:00
dm-bufio.c Merge branch 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2014-08-04 16:23:30 -07:00
dm-bufio.h dm snapshot: use dm-bufio prefetch 2014-01-14 23:23:03 -05:00
dm-builtin.c dm sysfs: fix a module unload race 2014-01-14 23:23:04 -05:00
dm-cache-block-types.h dm cache: remove remainder of distinct discard block size 2014-03-27 16:56:23 -04:00
dm-cache-metadata.c dm cache metadata: use dm-space-map-metadata.h defined size limits 2014-08-01 12:30:33 -04:00
dm-cache-metadata.h dm cache metadata: use dm-space-map-metadata.h defined size limits 2014-08-01 12:30:33 -04:00
dm-cache-policy-cleaner.c dm cache: policy change version from string to integer set 2013-03-20 17:21:27 +00:00
dm-cache-policy-internal.h dm cache: add remove_cblock method to policy interface 2013-11-11 11:37:50 -05:00
dm-cache-policy-mq.c dm cache mq: fix memory allocation failure for large cache devices 2014-02-28 12:18:29 -05:00
dm-cache-policy.c dm cache: add policy name to status output 2014-01-16 13:44:11 -05:00
dm-cache-policy.h dm cache: add policy name to status output 2014-01-16 13:44:11 -05:00
dm-cache-target.c dm cache: fix race causing dirty blocks to be marked as clean 2014-09-10 11:20:47 -04:00
dm-crypt.c dm crypt: fix access beyond the end of allocated space 2014-08-28 14:24:09 -04:00
dm-delay.c Merge branch 'for-3.14/core' of git://git.kernel.dk/linux-block 2014-01-30 11:19:05 -08:00
dm-era-target.c dm era: check for a non-NULL metadata object before closing it 2014-06-03 13:44:08 -04:00
dm-exception-store.c dm: replace simple_strtoul 2012-07-27 15:07:59 +01:00
dm-exception-store.h
…
dm-flakey.c block: Abstract out bvec iterator 2013-11-23 22:33:47 -08:00
dm-io.c dm io: simplify dec_count and sync_io 2014-08-01 12:30:30 -04:00
dm-ioctl.c dm: allow remove to be deferred 2013-11-09 18:20:22 -05:00
dm-kcopyd.c dm: stop using WQ_NON_REENTRANT 2013-08-23 09:02:13 -04:00
dm-linear.c block: Abstract out bvec iterator 2013-11-23 22:33:47 -08:00
dm-log-userspace-base.c dm log userspace: allow mark requests to piggyback on flush requests 2014-01-21 23:46:27 -05:00
dm-log-userspace-transfer.c connector: add portid to unicast in addition to broadcasting 2014-02-07 15:40:17 -08:00
dm-log-userspace-transfer.h
…
dm-log.c dm: use memweight() 2012-07-30 17:25:16 -07:00
dm-mpath.c dm mpath: eliminate pg_ready() wrapper 2014-08-01 12:30:31 -04:00
dm-mpath.h
…
dm-path-selector.c
…
dm-path-selector.h
…
dm-queue-length.c dm: reject trailing characters in sccanf input 2012-03-28 18:41:26 +01:00
dm-raid.c MD: Remember the last sync operation that was performed 2013-06-26 12:38:24 +10:00
dm-raid1.c dm raid1: fix immutable biovec related BUG when retrying read bio 2014-02-18 10:48:57 -05:00
dm-region-hash.c block: Abstract out bvec iterator 2013-11-23 22:33:47 -08:00
dm-round-robin.c dm: reject trailing characters in sccanf input 2012-03-28 18:41:26 +01:00
dm-service-time.c dm: reject trailing characters in sccanf input 2012-03-28 18:41:26 +01:00
dm-snap-persistent.c dm snapshot: fix metadata corruption 2014-03-03 17:58:13 -05:00
dm-snap-transient.c
…
dm-snap.c sched: Remove proliferation of wait_on_bit() action functions 2014-07-16 15:10:39 +02:00
dm-stats.c dm stats: initialize read-only module parameter 2013-12-10 19:13:21 -05:00
dm-stats.h dm: add statistics support 2013-09-05 20:46:06 -04:00
dm-stripe.c block: Abstract out bvec iterator 2013-11-23 22:33:47 -08:00
dm-switch.c dm switch: efficiently support repetitive patterns 2014-08-01 12:30:37 -04:00
dm-sysfs.c dm sysfs: fix a module unload race 2014-01-14 23:23:04 -05:00
dm-table.c dm table: propagate QUEUE_FLAG_NO_SG_MERGE 2014-08-10 20:54:49 -04:00
dm-target.c dm: allow error target to replace bio-based and request-based targets 2013-09-05 20:46:05 -04:00
dm-thin-metadata.c dm thin metadata: do not allow the data block size to change 2014-07-15 14:05:26 -04:00
dm-thin-metadata.h dm thin: ensure user takes action to validate data and metadata consistency 2014-03-05 15:25:35 -05:00
dm-thin.c dm thin: set minimum_io_size to pool's data block size 2014-08-01 12:30:35 -04:00
dm-uevent.c
…
dm-uevent.h
…
dm-verity.c dm verity: fix biovecs hash calculation regression 2014-04-15 12:19:24 -04:00
dm-zero.c dm crypt, dm zero: update author name following legal name change 2014-07-10 16:44:14 -04:00
dm.c dm: allocate a special workqueue for deferred device removal 2014-07-10 16:44:13 -04:00
dm.h dm table: make dm_table_supports_discards static 2014-08-01 12:30:34 -04:00
faulty.c block: Abstract out bvec iterator 2013-11-23 22:33:47 -08:00
linear.c block: Introduce new bio_split() 2013-11-23 22:33:57 -08:00
linear.h
…
md.c md: don't allow bitmap file to be added to raid0/linear. 2014-08-08 15:43:20 +10:00
md.h md/bitmap: don't abuse i_writecount for bitmap files. 2014-04-09 12:26:59 +10:00
multipath.c block: Abstract out bvec iterator 2013-11-23 22:33:47 -08:00
multipath.h
…
raid0.c md/raid0: check for bitmap compatability when changing raid levels. 2014-08-08 15:33:17 +10:00
raid0.h md: add proper merge_bvec handling to RAID0 and Linear. 2012-03-19 12:46:39 +11:00
raid1.c md/raid1: fix_read_error should act on all non-faulty devices. 2014-09-22 11:26:01 +10:00
raid1.h raid1: Rewrite the implementation of iobarrier. 2013-11-19 15:19:18 +11:00
raid5.c md/raid5: disable 'DISCARD' by default due to safety concerns. 2014-10-02 13:45:00 +10:00
raid5.h raid5: add an option to avoid copy data from bio to stripe cache 2014-05-29 16:59:47 +10:00
raid10.c md/raid10: always initialise ->state on newly allocated r10_bio 2014-08-19 17:20:27 +10:00
raid10.h MD RAID10: Improve redundancy for 'far' and 'offset' algorithms (part 1) 2013-02-26 11:55:30 +11:00