linux/drivers/md, branch v3.17

md/raid5: disable 'DISCARD' by default due to safety concerns.

2014-10-02T03:45:00Z

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 Cc: "Martin K. Petersen" Cc: Mike Snitzer Cc: Heinz Mauelshagen Cc: stable@vger.kernel.org (3.7+) Acked-by: Martin K. Petersen Acked-by: Mike Snitzer Fixes: 620125f2bf8ff0c4969b79653b54d7bcc9d40637 Signed-off-by: NeilBrown

Merge tag 'md/3.17-more-fixes' of git://git.neil.brown.name/md

2014-09-24T15:53:33Z

Pull bugfixes for md/raid1 from Neil Brown: "It is amazing how much easier it is to find bugs when you know one is there. Two bug reports resulted in finding 7 bugs! All are tagged for -stable. Those that can't cause (rare) data corruption, cause lockups. Particularly, but not only, fixing new "resync" code" * tag 'md/3.17-more-fixes' of git://git.neil.brown.name/md: md/raid1: fix_read_error should act on all non-faulty devices. md/raid1: count resync requests in nr_pending. md/raid1: update next_resync under resync_lock. md/raid1: Don't use next_resync to determine how far resync has progressed md/raid1: make sure resync waits for conflicting writes to complete. md/raid1: clean up request counts properly in close_sync() md/raid1: be more cautious where we read-balance during resync. md/raid1: intialise start_next_window for READ case to avoid hang

md/raid1: fix_read_error should act on all non-faulty devices.

2014-09-22T01:26:01Z

If a devices is being recovered it is not InSync and is not Faulty. If a read error is experienced on that device, fix_read_error() will be called, but it ignores non-InSync devices. So it will neither fix the error nor fail the device. It is incorrect that fix_read_error() ignores non-InSync devices. It should only ignore Faulty devices. So fix it. This became a bug when we allowed reading from a device that was being recovered. It is suitable for any subsequent -stable kernel. Fixes: da8840a747c0dbf49506ec906757a6b87b9741e9 Cc: stable@vger.kernel.org (v3.5+) Reported-by: Alexander Lyakas Tested-by: Alexander Lyakas Signed-off-by: NeilBrown

md/raid1: count resync requests in nr_pending.

2014-09-22T01:26:01Z

Both normal IO and resync IO can be retried with reschedule_retry() and so be counted into ->nr_queued, but only normal IO gets counted in ->nr_pending. Before the recent improvement to RAID1 resync there could only possibly have been one or the other on the queue. When handling a read failure it could only be normal IO. So when handle_read_error() called freeze_array() the fact that freeze_array only compares ->nr_queued against ->nr_pending was safe. But now that these two types can interleave, we can have both normal and resync IO requests queued, so we need to count them both in nr_pending. This error can lead to freeze_array() hanging if there is a read error, so it is suitable for -stable. Fixes: 79ef3a8aa1cb1523cc231c9a90a278333c21f761 cc: stable@vger.kernel.org (v3.13+) Reported-by: Brassow Jonathan Signed-off-by: NeilBrown

md/raid1: update next_resync under resync_lock.

2014-09-22T01:26:01Z

raise_barrier() uses next_resync as part of its calculations, so it really should be updated first, instead of afterwards. next_resync is always used under resync_lock so update it under resync lock to, just before it is used. That is safest. This could cause normal IO and resync IO to interact badly so it suitable for -stable. Fixes: 79ef3a8aa1cb1523cc231c9a90a278333c21f761 cc: stable@vger.kernel.org (v3.13+) Signed-off-by: NeilBrown

md/raid1: Don't use next_resync to determine how far resync has progressed

2014-09-22T01:26:01Z

next_resync is (approximately) the location for the next resync request. However it does *not* reliably determine the earliest location at which resync might be happening. This is because resync requests can complete out of order, and we only limit the number of current requests, not the distance from the earliest pending request to the latest. mddev->curr_resync_completed is a reliable indicator of the earliest position at which resync could be happening. It is updated less frequently, but is actually reliable which is more important. So use it to determine if a write request is before the region being resynced and so safe from conflict. This error can allow resync IO to interfere with normal IO which could lead to data corruption. Hence: stable. Fixes: 79ef3a8aa1cb1523cc231c9a90a278333c21f761 cc: stable@vger.kernel.org (v3.13+) Signed-off-by: NeilBrown

md/raid1: make sure resync waits for conflicting writes to complete.

2014-09-22T01:26:01Z

The resync/recovery process for raid1 was recently changed so that writes could happen in parallel with resync providing they were in different regions of the device. There is a problem though: While a write request will always wait for conflicting resync to complete, a resync request will *not* always wait for conflicting writes to complete. Two changes are needed to fix this: 1/ raise_barrier (which waits until it is safe to do resync) must wait until current_window_requests is zero 2/ wait_battier (which waits at the start of a new write request) must update current_window_requests if the request could possible conflict with a concurrent resync. As concurrent writes and resync can lead to data loss, this patch is suitable for -stable. Fixes: 79ef3a8aa1cb1523cc231c9a90a278333c21f761 Cc: stable@vger.kernel.org (v3.13+) Cc: majianpeng Signed-off-by: NeilBrown

md/raid1: clean up request counts properly in close_sync()

2014-09-22T01:26:01Z

If there are outstanding writes when close_sync is called, the change to ->start_next_window might cause them to decrement the wrong counter when they complete. Fix this by merging the two counters into the one that will be decremented. Having an incorrect value in a counter can cause raise_barrier() to hangs, so this is suitable for -stable. Fixes: 79ef3a8aa1cb1523cc231c9a90a278333c21f761 cc: stable@vger.kernel.org (v3.13+) Signed-off-by: NeilBrown

md/raid1: be more cautious where we read-balance during resync.

2014-09-22T00:26:41Z

commit 79ef3a8aa1cb1523cc231c9a90a278333c21f761 made it possible for reads to happen concurrently with resync. This means that we need to be more careful where read_balancing is allowed during resync - we can no longer be sure that any resync that has already started will definitely finish. So keep read_balancing to before recovery_cp, which is conservative but safe. This bug makes it possible to read from a device that doesn't have up-to-date data, so it can cause data corruption. So it is suitable for any kernel since 3.11. Fixes: 79ef3a8aa1cb1523cc231c9a90a278333c21f761 cc: stable@vger.kernel.org (v3.13+) Signed-off-by: NeilBrown

md/raid1: intialise start_next_window for READ case to avoid hang

2014-09-22T00:18:03Z

r1_bio->start_next_window is not initialised in the READ case, so allow_barrier may incorrectly decrement conf->current_window_requests which can cause raise_barrier() to block forever. Fixes: 79ef3a8aa1cb1523cc231c9a90a278333c21f761 cc: stable@vger.kernel.org (v3.13+) Reported-by: Brassow Jonathan Signed-off-by: NeilBrown