linux-stable.git/drivers/md/raid5.c, branch v4.2.7

md/raid5: fix locking in handle_stripe_clean_event()

2015-11-09T22:37:38+00:00

commit b8a9d66d043ffac116100775a469f05f5158c16f upstream.

After commit 566c09c53455 ("raid5: relieve lock contention in get_active_stripe()")
__find_stripe() is called under conf->hash_locks + hash.
But handle_stripe_clean_event() calls remove_hash() under
conf->device_lock.

Under some cirscumstances the hash chain can be circuited,
and we get an infinite loop with disabled interrupts and locked hash
lock in __find_stripe(). This leads to hard lockup on multiple CPUs
and following system crash.

I was able to reproduce this behavior on raid6 over 6 ssd disks.
The devices_handle_discard_safely option should be set to enable trim
support. The following script was used:

for i in `seq 1 32`; do
    dd if=/dev/zero of=large$i bs=10M count=100 &
done

neilb: original was against a 3.x kernel.  I forward-ported
  to 4.3-rc.  This verison is suitable for any kernel since
  Commit: 59fc630b8b5f ("RAID5: batch adjacent full stripe write")
  (v4.1+).  I'll post a version for earlier kernels to stable.

Signed-off-by: Roman Gushchin 
Fixes: 566c09c53455 ("raid5: relieve lock contention in get_active_stripe()")
Signed-off-by: NeilBrown 
Cc: Shaohua Li 
Signed-off-by: Greg Kroah-Hartman

md/raid5: don't let shrink_slab shrink too far.

2015-08-03T07:10:56+00:00

I have a report of drop_one_stripe() called from
raid5_cache_scan() apparently finding ->max_nr_stripes == 0.

This should not be allowed.

So add a test to keep max_nr_stripes above min_nr_stripes.

Also use a 'mask' rather than a 'mod' in drop_one_stripe
to ensure 'hash' is valid even if max_nr_stripes does reach zero.


Fixes: edbe83ab4c27 ("md/raid5: allow the stripe_cache to grow and shrink.")
Cc: stable@vger.kernel.org (4.1 - please release with 2d5b569b665)
Reported-by: Tomas Papan 
Signed-off-by: NeilBrown

md/raid5: clear R5_NeedReplace when no longer needed.

2015-07-24T03:38:04+00:00

This flag is currently never cleared, which can in rare cases
trigger a warn-on if it is still set but the block isn't
InSync.

So clear it when it isn't need, which includes if the replacement
device has failed.

Signed-off-by: NeilBrown

md/raid5: avoid races when changing cache size.

2015-07-22T04:04:15+00:00

Cache size can grow or shrink due to various pressures at
any time.  So when we resize the cache as part of a 'grow'
operation (i.e. change the size to allow more devices) we need
to blocks that automatic growing/shrinking.

So introduce a mutex.  auto grow/shrink uses mutex_trylock()
and just doesn't bother if there is a blockage.
Resizing the whole cache holds the mutex to ensure that
the correct number of new stripes is allocated.

This bug can result in some stripes not being freed when an
array is stopped.  This leads to the kmem_cache not being
freed and a subsequent array can try to use the same kmem_cache
and get confused.

Fixes: edbe83ab4c27 ("md/raid5: allow the stripe_cache to grow and shrink.")
Cc: stable@vger.kernel.org (4.1 - please delay until 2 weeks after release of 4.2)
Signed-off-by: NeilBrown

md/raid5: ignore released_stripes check

2015-06-17T00:00:33+00:00

conf->released_stripes list isn't always related to where there are
free stripes pending. Active stripes can be in the list too.
And even free stripes were active very recently.

Signed-off-by: Shaohua Li 
Signed-off-by: NeilBrown

md/raid5: per hash value and exclusive wait_for_stripe

2015-06-17T00:00:27+00:00

I noticed heavy spin lock contention at get_active_stripe() with fsmark
multiple thread write workloads.

Here is how this hot contention comes from. We have limited stripes, and
it's a multiple thread write workload. Hence, those stripes will be taken
soon, which puts later processes to sleep for waiting free stripes. When
enough stripes(>= 1/4 total stripes) are released, all process are woken,
trying to get the lock. But there is one only being able to get this lock
for each hash lock, making other processes spinning out there for acquiring
the lock.

Thus, it's effectiveless to wakeup all processes and let them battle for
a lock that permits one to access only each time. Instead, we could make
it be a exclusive wake up: wake up one process only. That avoids the heavy
spin lock contention naturally.

To do the exclusive wake up, we've to split wait_for_stripe into multiple
wait queues, to make it per hash value, just like the hash lock.

Here are some test results I have got with this patch applied(all test run
3 times):

`fsmark.files_per_sec'
=====================

next-20150317                 this patch
-------------------------     -------------------------
metric_value     ±stddev      metric_value     ±stddev     change      testbox/benchmark/testcase-params
-------------------------     -------------------------   --------     ------------------------------
      25.600     ±0.0              92.700     ±2.5          262.1%     ivb44/fsmark/1x-64t-4BRD_12G-RAID5-btrfs-4M-30G-fsyncBeforeClose
      25.600     ±0.0              77.800     ±0.6          203.9%     ivb44/fsmark/1x-64t-9BRD_6G-RAID5-btrfs-4M-30G-fsyncBeforeClose
      32.000     ±0.0              93.800     ±1.7          193.1%     ivb44/fsmark/1x-64t-4BRD_12G-RAID5-ext4-4M-30G-fsyncBeforeClose
      32.000     ±0.0              81.233     ±1.7          153.9%     ivb44/fsmark/1x-64t-9BRD_6G-RAID5-ext4-4M-30G-fsyncBeforeClose
      48.800     ±14.5             99.667     ±2.0          104.2%     ivb44/fsmark/1x-64t-4BRD_12G-RAID5-xfs-4M-30G-fsyncBeforeClose
       6.400     ±0.0              12.800     ±0.0          100.0%     ivb44/fsmark/1x-64t-3HDD-RAID5-btrfs-4M-40G-fsyncBeforeClose
      63.133     ±8.2              82.800     ±0.7           31.2%     ivb44/fsmark/1x-64t-9BRD_6G-RAID5-xfs-4M-30G-fsyncBeforeClose
     245.067     ±0.7             306.567     ±7.9           25.1%     ivb44/fsmark/1x-64t-4BRD_12G-RAID5-f2fs-4M-30G-fsyncBeforeClose
      17.533     ±0.3              21.000     ±0.8           19.8%     ivb44/fsmark/1x-1t-3HDD-RAID5-xfs-4M-40G-fsyncBeforeClose
     188.167     ±1.9             215.033     ±3.1           14.3%     ivb44/fsmark/1x-1t-4BRD_12G-RAID5-btrfs-4M-30G-NoSync
     254.500     ±1.8             290.733     ±2.4           14.2%     ivb44/fsmark/1x-1t-9BRD_6G-RAID5-btrfs-4M-30G-NoSync

`time.system_time'
=====================

next-20150317                 this patch
-------------------------    -------------------------
metric_value     ±stddev     metric_value     ±stddev     change       testbox/benchmark/testcase-params
-------------------------    -------------------------    --------     ------------------------------
    7235.603     ±1.2             185.163     ±1.9          -97.4%     ivb44/fsmark/1x-64t-4BRD_12G-RAID5-btrfs-4M-30G-fsyncBeforeClose
    7666.883     ±2.9             202.750     ±1.0          -97.4%     ivb44/fsmark/1x-64t-9BRD_6G-RAID5-btrfs-4M-30G-fsyncBeforeClose
   14567.893     ±0.7             421.230     ±0.4          -97.1%     ivb44/fsmark/1x-64t-3HDD-RAID5-btrfs-4M-40G-fsyncBeforeClose
    3697.667     ±14.0            148.190     ±1.7          -96.0%     ivb44/fsmark/1x-64t-4BRD_12G-RAID5-xfs-4M-30G-fsyncBeforeClose
    5572.867     ±3.8             310.717     ±1.4          -94.4%     ivb44/fsmark/1x-64t-9BRD_6G-RAID5-ext4-4M-30G-fsyncBeforeClose
    5565.050     ±0.5             313.277     ±1.5          -94.4%     ivb44/fsmark/1x-64t-4BRD_12G-RAID5-ext4-4M-30G-fsyncBeforeClose
    2420.707     ±17.1            171.043     ±2.7          -92.9%     ivb44/fsmark/1x-64t-9BRD_6G-RAID5-xfs-4M-30G-fsyncBeforeClose
    3743.300     ±4.6             379.827     ±3.5          -89.9%     ivb44/fsmark/1x-64t-3HDD-RAID5-ext4-4M-40G-fsyncBeforeClose
    3308.687     ±6.3             363.050     ±2.0          -89.0%     ivb44/fsmark/1x-64t-3HDD-RAID5-xfs-4M-40G-fsyncBeforeClose

Where,

     1x: where 'x' means iterations or loop, corresponding to the 'L' option of fsmark

     1t, 64t: where 't' means thread

     4M: means the single file size, corresponding to the '-s' option of fsmark
     40G, 30G, 120G: means the total test size

     4BRD_12G: BRD is the ramdisk, where '4' means 4 ramdisk, and where '12G' means
               the size of one ramdisk. So, it would be 48G in total. And we made a
               raid on those ramdisk

As you can see, though there are no much performance gain for hard disk
workload, the system time is dropped heavily, up to 97%. And as expected,
the performance increased a lot, up to 260%, for fast device(ram disk).

v2: use bits instead of array to note down wait queue need to wake up.

Signed-off-by: Yuanhan Liu 
Signed-off-by: NeilBrown

md/raid5: split wait_for_stripe and introduce wait_for_quiescent

2015-06-17T00:00:21+00:00

I noticed heavy spin lock contention at get_active_stripe(), introduced
at being wake up stage, where a bunch of processes try to re-hold the
spin lock again.

After giving some thoughts on this issue, I found the lock could be
relieved(and even avoided) if we turn the wait_for_stripe to per
waitqueue for each lock hash and make the wake up exclusive: wake up
one process each time, which avoids the lock contention naturally.

Before go hacking with wait_for_stripe, I found it actually has 2
usages: for the array to enter or leave the quiescent state, and also
to wait for an available stripe in each of the hash lists.

So this patch splits the first usage off into a separate wait_queue,
wait_for_quiescent, and the next patch will turn the second usage into
one waitqueue for each hash value, and make it exclusive, to relieve
the lock contention.

v2: wake_up(wait_for_quiescent) when (active_stripes == 0)
    Commit log refactor suggestion from Neil.

Signed-off-by: Yuanhan Liu 
Signed-off-by: NeilBrown

md: make sure MD_RECOVERY_DONE is clear before starting recovery/resync

2015-06-12T10:16:33+00:00

MD_RECOVERY_DONE is normally cleared by md_check_recovery after a
resync etc finished.  However it is possible for raid5_start_reshape
to race and start a reshape before MD_RECOVERY_DONE is cleared.  This
can lean to multiple reshapes running at the same time, which isn't
good.

To make sure it is cleared before starting a reshape, and also clear
it when reaping a thread, just to be safe.

Signed-off-by: NeilBrown

md/raid5: break stripe-batches when the array has failed.

2015-05-28T01:48:59+00:00

Once the array has too much failure, we need to break
stripe-batches up so they can all be dealt with.

Signed-off-by: NeilBrown

md/raid5: call break_stripe_batch_list from handle_stripe_clean_event

2015-05-28T01:47:02+00:00

Now that the code in break_stripe_batch_list() is nearly identical
to the end of handle_stripe_clean_event, replace the later
with a function call.

The only remaining difference of any interest is the masking that is
applieds to dev[i].flags copied from head_sh.
R5_WriteError certainly isn't wanted as it is set per-stripe, not
per-patch.  R5_Overlap isn't wanted as it is explicitly handled.

Signed-off-by: NeilBrown