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  1. 26 5月, 2016 1 次提交
  3. 06 5月, 2016 5 次提交
    • A
      btrfs: fix lock dep warning move scratch super outside of chunk_mutex · 48b3b9d4
      由 Anand Jain 提交于 
      Move scratch super outside of the chunk lock to avoid below
lockdep warning. The better place to scratch super is in
the function btrfs_rm_dev_replace_free_srcdev() just before
free_device, which is outside of the chunk lock as well.

To reproduce:
  (fresh boot)
  mkfs.btrfs -f -draid5 -mraid5 /dev/sdc /dev/sdd /dev/sde
  mount /dev/sdc /btrfs
  dd if=/dev/zero of=/btrfs/tf1 bs=4096 count=100
  (get devmgt from https://github.com/asj/devmgt.git)
  devmgt detach /dev/sde
  dd if=/dev/zero of=/btrfs/tf1 bs=4096 count=100
  sync
  btrfs replace start -Brf 3 /dev/sdf /btrfs <--
  devmgt attach host7

======================================================
[ INFO: possible circular locking dependency detected ]
4.6.0-rc2asj+ #1 Not tainted
---------------------------------------------------

btrfs/2174 is trying to acquire lock:
(sb_writers){.+.+.+}, at:
[<ffffffff812449b4>] __sb_start_write+0xb4/0xf0

but task is already holding lock:
(&fs_info->chunk_mutex){+.+.+.}, at:
[<ffffffffa05c5f55>] btrfs_dev_replace_finishing+0x145/0x980 [btrfs]

which lock already depends on the new lock.

Chain exists of:
sb_writers --> &fs_devs->device_list_mutex --> &fs_info->chunk_mutex
Possible unsafe locking scenario:
CPU0				CPU1
----				----
lock(&fs_info->chunk_mutex);
				lock(&fs_devs->device_list_mutex);
				lock(&fs_info->chunk_mutex);
lock(sb_writers);

*** DEADLOCK ***

-> #0 (sb_writers){.+.+.+}:
[<ffffffff810e6415>] __lock_acquire+0x1bc5/0x1ee0
[<ffffffff810e707e>] lock_acquire+0xbe/0x210
[<ffffffff810df49a>] percpu_down_read+0x4a/0xa0
[<ffffffff812449b4>] __sb_start_write+0xb4/0xf0
[<ffffffff81265534>] mnt_want_write+0x24/0x50
[<ffffffff812508a2>] path_openat+0x952/0x1190
[<ffffffff81252451>] do_filp_open+0x91/0x100
[<ffffffff8123f5cc>] file_open_name+0xfc/0x140
[<ffffffff8123f643>] filp_open+0x33/0x60
[<ffffffffa0572bb6>] update_dev_time+0x16/0x40 [btrfs]
[<ffffffffa057f60d>] btrfs_scratch_superblocks+0x5d/0xb0 [btrfs]
[<ffffffffa057f70e>] btrfs_rm_dev_replace_remove_srcdev+0xae/0xd0 [btrfs]
[<ffffffffa05c62c5>] btrfs_dev_replace_finishing+0x4b5/0x980 [btrfs]
[<ffffffffa05c6ae8>] btrfs_dev_replace_start+0x358/0x530 [btrfs]
Signed-off-by: NAnand Jain <anand.jain@oracle.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>
      48b3b9d4
    • J
      Btrfs: remove BUG_ON()'s in btrfs_map_block · e042d1ec
      由 Josef Bacik 提交于 
      btrfs_map_block can go horribly wrong in the face of fs corruption, lets agree
to not be assholes and panic at any possible chance things are all fucked up.
Signed-off-by: NJosef Bacik <jbacik@fb.com>
[ removed type casts ]
Signed-off-by: NDavid Sterba <dsterba@suse.com>
      e042d1ec
    • L
      Btrfs: fix divide error upon chunk's stripe_len · 3d8da678
      由 Liu Bo 提交于 
      The struct 'map_lookup' uses type int for @stripe_len, while
btrfs_chunk_stripe_len() can return a u64 value, and it may end up with
@stripe_len being undefined value and it can lead to 'divide error' in
 __btrfs_map_block().

This changes 'map_lookup' to use type u64 for stripe_len, also right now
we only use BTRFS_STRIPE_LEN for stripe_len, so this adds a valid checker for
BTRFS_STRIPE_LEN.
Reported-by: NVegard Nossum <vegard.nossum@oracle.com>
Reported-by: NQuentin Casasnovas <quentin.casasnovas@oracle.com>
Signed-off-by: NLiu Bo <bo.li.liu@oracle.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
[ folded division fix to scrub_raid56_parity ]
Signed-off-by: NDavid Sterba <dsterba@suse.com>
      3d8da678
    • A
      btrfs: fix lock dep warning, move scratch dev out of device_list_mutex and uuid_mutex · 779bf3fe
      由 Anand Jain 提交于 
      When the replace target fails, the target device will be taken
out of fs device list, scratch + update_dev_time and freed. However
we could do the scratch  + update_dev_time and free part after the
device has been taken out of device list, so that we don't have to
hold the device_list_mutex and uuid_mutex locks.

Reported issue:

[ 5375.718845] ======================================================
[ 5375.718846] [ INFO: possible circular locking dependency detected ]
[ 5375.718849] 4.4.5-scst31x-debug-11+ #40 Not tainted
[ 5375.718849] -------------------------------------------------------
[ 5375.718851] btrfs-health/4662 is trying to acquire lock:
[ 5375.718861]  (sb_writers){.+.+.+}, at: [<ffffffff812214f7>] __sb_start_write+0xb7/0xf0
[ 5375.718862]
[ 5375.718862] but task is already holding lock:
[ 5375.718907]  (&fs_devs->device_list_mutex){+.+.+.}, at: [<ffffffffa028263c>] btrfs_destroy_dev_replace_tgtdev+0x3c/0x150 [btrfs]
[ 5375.718907]
[ 5375.718907] which lock already depends on the new lock.
[ 5375.718907]
[ 5375.718908]
[ 5375.718908] the existing dependency chain (in reverse order) is:
[ 5375.718911]
[ 5375.718911] -> #3 (&fs_devs->device_list_mutex){+.+.+.}:
[ 5375.718917]        [<ffffffff810da4be>] lock_acquire+0xce/0x1e0
[ 5375.718921]        [<ffffffff81633949>] mutex_lock_nested+0x69/0x3c0
[ 5375.718940]        [<ffffffffa0219bf6>] btrfs_show_devname+0x36/0x210 [btrfs]
[ 5375.718945]        [<ffffffff81267079>] show_vfsmnt+0x49/0x150
[ 5375.718948]        [<ffffffff81240b07>] m_show+0x17/0x20
[ 5375.718951]        [<ffffffff81246868>] seq_read+0x2d8/0x3b0
[ 5375.718955]        [<ffffffff8121df28>] __vfs_read+0x28/0xd0
[ 5375.718959]        [<ffffffff8121e806>] vfs_read+0x86/0x130
[ 5375.718962]        [<ffffffff8121f4c9>] SyS_read+0x49/0xa0
[ 5375.718966]        [<ffffffff81637976>] entry_SYSCALL_64_fastpath+0x16/0x7a
[ 5375.718968]
[ 5375.718968] -> #2 (namespace_sem){+++++.}:
[ 5375.718971]        [<ffffffff810da4be>] lock_acquire+0xce/0x1e0
[ 5375.718974]        [<ffffffff81635199>] down_write+0x49/0x80
[ 5375.718977]        [<ffffffff81243593>] lock_mount+0x43/0x1c0
[ 5375.718979]        [<ffffffff81243c13>] do_add_mount+0x23/0xd0
[ 5375.718982]        [<ffffffff81244afb>] do_mount+0x27b/0xe30
[ 5375.718985]        [<ffffffff812459dc>] SyS_mount+0x8c/0xd0
[ 5375.718988]        [<ffffffff81637976>] entry_SYSCALL_64_fastpath+0x16/0x7a
[ 5375.718991]
[ 5375.718991] -> #1 (&sb->s_type->i_mutex_key#5){+.+.+.}:
[ 5375.718994]        [<ffffffff810da4be>] lock_acquire+0xce/0x1e0
[ 5375.718996]        [<ffffffff81633949>] mutex_lock_nested+0x69/0x3c0
[ 5375.719001]        [<ffffffff8122d608>] path_openat+0x468/0x1360
[ 5375.719004]        [<ffffffff8122f86e>] do_filp_open+0x7e/0xe0
[ 5375.719007]        [<ffffffff8121da7b>] do_sys_open+0x12b/0x210
[ 5375.719010]        [<ffffffff8121db7e>] SyS_open+0x1e/0x20
[ 5375.719013]        [<ffffffff81637976>] entry_SYSCALL_64_fastpath+0x16/0x7a
[ 5375.719015]
[ 5375.719015] -> #0 (sb_writers){.+.+.+}:
[ 5375.719018]        [<ffffffff810d97ca>] __lock_acquire+0x17ba/0x1ae0
[ 5375.719021]        [<ffffffff810da4be>] lock_acquire+0xce/0x1e0
[ 5375.719026]        [<ffffffff810d3bef>] percpu_down_read+0x4f/0xa0
[ 5375.719028]        [<ffffffff812214f7>] __sb_start_write+0xb7/0xf0
[ 5375.719031]        [<ffffffff81242eb4>] mnt_want_write+0x24/0x50
[ 5375.719035]        [<ffffffff8122ded2>] path_openat+0xd32/0x1360
[ 5375.719037]        [<ffffffff8122f86e>] do_filp_open+0x7e/0xe0
[ 5375.719040]        [<ffffffff8121d8a4>] file_open_name+0xe4/0x130
[ 5375.719043]        [<ffffffff8121d923>] filp_open+0x33/0x60
[ 5375.719073]        [<ffffffffa02776a6>] update_dev_time+0x16/0x40 [btrfs]
[ 5375.719099]        [<ffffffffa02825be>] btrfs_scratch_superblocks+0x4e/0x90 [btrfs]
[ 5375.719123]        [<ffffffffa0282665>] btrfs_destroy_dev_replace_tgtdev+0x65/0x150 [btrfs]
[ 5375.719150]        [<ffffffffa02c6c80>] btrfs_dev_replace_finishing+0x6b0/0x990 [btrfs]
[ 5375.719175]        [<ffffffffa02c729e>] btrfs_dev_replace_start+0x33e/0x540 [btrfs]
[ 5375.719199]        [<ffffffffa02c7f58>] btrfs_auto_replace_start+0xf8/0x140 [btrfs]
[ 5375.719222]        [<ffffffffa02464e6>] health_kthread+0x246/0x490 [btrfs]
[ 5375.719225]        [<ffffffff810a70df>] kthread+0xef/0x110
[ 5375.719229]        [<ffffffff81637d2f>] ret_from_fork+0x3f/0x70
[ 5375.719230]
[ 5375.719230] other info that might help us debug this:
[ 5375.719230]
[ 5375.719233] Chain exists of:
[ 5375.719233]   sb_writers --> namespace_sem --> &fs_devs->device_list_mutex
[ 5375.719233]
[ 5375.719234]  Possible unsafe locking scenario:
[ 5375.719234]
[ 5375.719234]        CPU0                    CPU1
[ 5375.719235]        ----                    ----
[ 5375.719236]   lock(&fs_devs->device_list_mutex);
[ 5375.719238]                                lock(namespace_sem);
[ 5375.719239]                                lock(&fs_devs->device_list_mutex);
[ 5375.719241]   lock(sb_writers);
[ 5375.719241]
[ 5375.719241]  *** DEADLOCK ***
[ 5375.719241]
[ 5375.719243] 4 locks held by btrfs-health/4662:
[ 5375.719266]  #0:  (&fs_info->health_mutex){+.+.+.}, at: [<ffffffffa0246303>] health_kthread+0x63/0x490 [btrfs]
[ 5375.719293]  #1:  (&fs_info->dev_replace.lock_finishing_cancel_unmount){+.+.+.}, at: [<ffffffffa02c6611>] btrfs_dev_replace_finishing+0x41/0x990 [btrfs]
[ 5375.719319]  #2:  (uuid_mutex){+.+.+.}, at: [<ffffffffa0282620>] btrfs_destroy_dev_replace_tgtdev+0x20/0x150 [btrfs]
[ 5375.719343]  #3:  (&fs_devs->device_list_mutex){+.+.+.}, at: [<ffffffffa028263c>] btrfs_destroy_dev_replace_tgtdev+0x3c/0x150 [btrfs]
[ 5375.719343]
[ 5375.719343] stack backtrace:
[ 5375.719347] CPU: 2 PID: 4662 Comm: btrfs-health Not tainted 4.4.5-scst31x-debug-11+ #40
[ 5375.719348] Hardware name: Supermicro SYS-6018R-WTRT/X10DRW-iT, BIOS 1.0c 01/07/2015
[ 5375.719352]  0000000000000000 ffff880856f73880 ffffffff813529e3 ffffffff826182a0
[ 5375.719354]  ffffffff8260c090 ffff880856f738c0 ffffffff810d667c ffff880856f73930
[ 5375.719357]  ffff880861f32b40 ffff880861f32b68 0000000000000003 0000000000000004
[ 5375.719357] Call Trace:
[ 5375.719363]  [<ffffffff813529e3>] dump_stack+0x85/0xc2
[ 5375.719366]  [<ffffffff810d667c>] print_circular_bug+0x1ec/0x260
[ 5375.719369]  [<ffffffff810d97ca>] __lock_acquire+0x17ba/0x1ae0
[ 5375.719373]  [<ffffffff810f606d>] ? debug_lockdep_rcu_enabled+0x1d/0x20
[ 5375.719376]  [<ffffffff810da4be>] lock_acquire+0xce/0x1e0
[ 5375.719378]  [<ffffffff812214f7>] ? __sb_start_write+0xb7/0xf0
[ 5375.719383]  [<ffffffff810d3bef>] percpu_down_read+0x4f/0xa0
[ 5375.719385]  [<ffffffff812214f7>] ? __sb_start_write+0xb7/0xf0
[ 5375.719387]  [<ffffffff812214f7>] __sb_start_write+0xb7/0xf0
[ 5375.719389]  [<ffffffff81242eb4>] mnt_want_write+0x24/0x50
[ 5375.719393]  [<ffffffff8122ded2>] path_openat+0xd32/0x1360
[ 5375.719415]  [<ffffffffa02462a0>] ? btrfs_congested_fn+0x180/0x180 [btrfs]
[ 5375.719418]  [<ffffffff810f606d>] ? debug_lockdep_rcu_enabled+0x1d/0x20
[ 5375.719420]  [<ffffffff8122f86e>] do_filp_open+0x7e/0xe0
[ 5375.719423]  [<ffffffff810f615d>] ? rcu_read_lock_sched_held+0x6d/0x80
[ 5375.719426]  [<ffffffff81201a9b>] ? kmem_cache_alloc+0x26b/0x5d0
[ 5375.719430]  [<ffffffff8122e7d4>] ? getname_kernel+0x34/0x120
[ 5375.719433]  [<ffffffff8121d8a4>] file_open_name+0xe4/0x130
[ 5375.719436]  [<ffffffff8121d923>] filp_open+0x33/0x60
[ 5375.719462]  [<ffffffffa02776a6>] update_dev_time+0x16/0x40 [btrfs]
[ 5375.719485]  [<ffffffffa02825be>] btrfs_scratch_superblocks+0x4e/0x90 [btrfs]
[ 5375.719506]  [<ffffffffa0282665>] btrfs_destroy_dev_replace_tgtdev+0x65/0x150 [btrfs]
[ 5375.719530]  [<ffffffffa02c6c80>] btrfs_dev_replace_finishing+0x6b0/0x990 [btrfs]
[ 5375.719554]  [<ffffffffa02c6b23>] ? btrfs_dev_replace_finishing+0x553/0x990 [btrfs]
[ 5375.719576]  [<ffffffffa02c729e>] btrfs_dev_replace_start+0x33e/0x540 [btrfs]
[ 5375.719598]  [<ffffffffa02c7f58>] btrfs_auto_replace_start+0xf8/0x140 [btrfs]
[ 5375.719621]  [<ffffffffa02464e6>] health_kthread+0x246/0x490 [btrfs]
[ 5375.719641]  [<ffffffffa02463d8>] ? health_kthread+0x138/0x490 [btrfs]
[ 5375.719661]  [<ffffffffa02462a0>] ? btrfs_congested_fn+0x180/0x180 [btrfs]
[ 5375.719663]  [<ffffffff810a70df>] kthread+0xef/0x110
[ 5375.719666]  [<ffffffff810a6ff0>] ? kthread_create_on_node+0x200/0x200
[ 5375.719669]  [<ffffffff81637d2f>] ret_from_fork+0x3f/0x70
[ 5375.719672]  [<ffffffff810a6ff0>] ? kthread_create_on_node+0x200/0x200
[ 5375.719697] ------------[ cut here ]------------
Signed-off-by: NAnand Jain <anand.jain@oracle.com>
Reported-by: NYauhen Kharuzhy <yauhen.kharuzhy@zavadatar.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>
      779bf3fe
    • A
      btrfs: allow balancing to dup with multi-device · 88be159c
      由 Austin S. Hemmelgarn 提交于 
      Currently, we don't allow the user to try and rebalance to a dup profile
on a multi-device filesystem.  In most cases, this is a perfectly sensible
restriction as raid1 uses the same amount of space and provides better
protection.

However, when reshaping a multi-device filesystem down to a single device
filesystem, this requires the user to convert metadata and system chunks
to single profile before deleting devices, and then convert again to dup,
which leaves a period of time where metadata integrity is reduced.

This patch removes the single-device-only restriction from converting to
dup profile to remove this potential data integrity reduction.
Signed-off-by: NAustin S. Hemmelgarn <ahferroin7@gmail.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>
      88be159c
  5. 04 5月, 2016 2 次提交
  7. 28 4月, 2016 16 次提交
  9. 05 4月, 2016 1 次提交
    • K
      mm, fs: get rid of PAGE_CACHE_* and page_cache_{get,release} macros · 09cbfeaf
      由 Kirill A. Shutemov 提交于 
      PAGE_CACHE_{SIZE,SHIFT,MASK,ALIGN} macros were introduced *long* time
ago with promise that one day it will be possible to implement page
cache with bigger chunks than PAGE_SIZE.

This promise never materialized.  And unlikely will.

We have many places where PAGE_CACHE_SIZE assumed to be equal to
PAGE_SIZE.  And it's constant source of confusion on whether
PAGE_CACHE_* or PAGE_* constant should be used in a particular case,
especially on the border between fs and mm.

Global switching to PAGE_CACHE_SIZE != PAGE_SIZE would cause to much
breakage to be doable.

Let's stop pretending that pages in page cache are special.  They are
not.

The changes are pretty straight-forward:

 - <foo> << (PAGE_CACHE_SHIFT - PAGE_SHIFT) -> <foo>;

 - <foo> >> (PAGE_CACHE_SHIFT - PAGE_SHIFT) -> <foo>;

 - PAGE_CACHE_{SIZE,SHIFT,MASK,ALIGN} -> PAGE_{SIZE,SHIFT,MASK,ALIGN};

 - page_cache_get() -> get_page();

 - page_cache_release() -> put_page();

This patch contains automated changes generated with coccinelle using
script below.  For some reason, coccinelle doesn't patch header files.
I've called spatch for them manually.

The only adjustment after coccinelle is revert of changes to
PAGE_CAHCE_ALIGN definition: we are going to drop it later.

There are few places in the code where coccinelle didn't reach.  I'll
fix them manually in a separate patch.  Comments and documentation also
will be addressed with the separate patch.

virtual patch

@@
expression E;
@@
- E << (PAGE_CACHE_SHIFT - PAGE_SHIFT)
+ E

@@
expression E;
@@
- E >> (PAGE_CACHE_SHIFT - PAGE_SHIFT)
+ E

@@
@@
- PAGE_CACHE_SHIFT
+ PAGE_SHIFT

@@
@@
- PAGE_CACHE_SIZE
+ PAGE_SIZE

@@
@@
- PAGE_CACHE_MASK
+ PAGE_MASK

@@
expression E;
@@
- PAGE_CACHE_ALIGN(E)
+ PAGE_ALIGN(E)

@@
expression E;
@@
- page_cache_get(E)
+ get_page(E)

@@
expression E;
@@
- page_cache_release(E)
+ put_page(E)
Signed-off-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: NMichal Hocko <mhocko@suse.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      09cbfeaf
  11. 14 3月, 2016 1 次提交
  13. 23 2月, 2016 1 次提交
    • L
      Btrfs: fix lockdep deadlock warning due to dev_replace · 73beece9
      由 Liu Bo 提交于 
      Xfstests btrfs/011 complains about a deadlock warning,

[ 1226.649039] =========================================================
[ 1226.649039] [ INFO: possible irq lock inversion dependency detected ]
[ 1226.649039] 4.1.0+ #270 Not tainted
[ 1226.649039] ---------------------------------------------------------
[ 1226.652955] kswapd0/46 just changed the state of lock:
[ 1226.652955]  (&delayed_node->mutex){+.+.-.}, at: [<ffffffff81458735>] __btrfs_release_delayed_node+0x45/0x1d0
[ 1226.652955] but this lock took another, RECLAIM_FS-unsafe lock in the past:
[ 1226.652955]  (&fs_info->dev_replace.lock){+.+.+.}

and interrupts could create inverse lock ordering between them.

[ 1226.652955]
other info that might help us debug this:
[ 1226.652955] Chain exists of:
  &delayed_node->mutex --> &found->groups_sem --> &fs_info->dev_replace.lock

[ 1226.652955]  Possible interrupt unsafe locking scenario:

[ 1226.652955]        CPU0                    CPU1
[ 1226.652955]        ----                    ----
[ 1226.652955]   lock(&fs_info->dev_replace.lock);
[ 1226.652955]                                local_irq_disable();
[ 1226.652955]                                lock(&delayed_node->mutex);
[ 1226.652955]                                lock(&found->groups_sem);
[ 1226.652955]   <Interrupt>
[ 1226.652955]     lock(&delayed_node->mutex);
[ 1226.652955]
 *** DEADLOCK ***

Commit 084b6e7c ("btrfs: Fix a lockdep warning when running xfstest.") tried
to fix a similar one that has the exactly same warning, but with that, we still
run to this.

The above lock chain comes from
btrfs_commit_transaction
  ->btrfs_run_delayed_items
    ...
    ->__btrfs_update_delayed_inode
      ...
      ->__btrfs_cow_block
         ...
         ->find_free_extent
            ->cache_block_group
              ->load_free_space_cache
                ->btrfs_readpages
                  ->submit_one_bio
                    ...
                    ->__btrfs_map_block
                      ->btrfs_dev_replace_lock

However, with high memory pressure, tasks which hold dev_replace.lock can
be interrupted by kswapd and then kswapd is intended to release memory occupied
by superblock, inodes and dentries, where we may call evict_inode, and it comes
to

[ 1226.652955]  [<ffffffff81458735>] __btrfs_release_delayed_node+0x45/0x1d0
[ 1226.652955]  [<ffffffff81459e74>] btrfs_remove_delayed_node+0x24/0x30
[ 1226.652955]  [<ffffffff8140c5fe>] btrfs_evict_inode+0x34e/0x700

delayed_node->mutex may be acquired in __btrfs_release_delayed_node(), and it leads
to a ABBA deadlock.

To fix this, we can use "blocking rwlock" used in the case of extent_buffer, but
things are simpler here since we only needs read's spinlock to blocking lock.

With this, btrfs/011 no more produces warnings in dmesg.
Signed-off-by: NLiu Bo <bo.li.liu@oracle.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>
      73beece9
  15. 11 2月, 2016 3 次提交
  17. 30 1月, 2016 1 次提交
  19. 22 1月, 2016 1 次提交
  21. 20 1月, 2016 4 次提交
  23. 19 1月, 2016 1 次提交
  25. 16 1月, 2016 2 次提交
  27. 08 1月, 2016 1 次提交
    • F
      Btrfs: fix fitrim discarding device area reserved for boot loader's use · 8cdc7c5b
      由 Filipe Manana 提交于 
      As of the 4.3 kernel release, the fitrim ioctl can now discard any region
of a disk that is not allocated to any chunk/block group, including the
first megabyte which is used for our primary superblock and by the boot
loader (grub for example).

Fix this by not allowing to trim/discard any region in the device starting
with an offset not greater than min(alloc_start_mount_option, 1Mb), just
as it was not possible before 4.3.

A reproducer test case for xfstests follows.

  seq=`basename $0`
  seqres=$RESULT_DIR/$seq
  echo "QA output created by $seq"
  tmp=/tmp/$$
  status=1	# failure is the default!
  trap "_cleanup; exit \$status" 0 1 2 3 15

  _cleanup()
  {
      cd /
      rm -f $tmp.*
  }

  # get standard environment, filters and checks
  . ./common/rc
  . ./common/filter

  # real QA test starts here
  _need_to_be_root
  _supported_fs btrfs
  _supported_os Linux
  _require_scratch

  rm -f $seqres.full

  _scratch_mkfs >>$seqres.full 2>&1

  # Write to the [0, 64Kb[ and [68Kb, 1Mb[ ranges of the device. These ranges are
  # reserved for a boot loader to use (GRUB for example) and btrfs should never
  # use them - neither for allocating metadata/data nor should trim/discard them.
  # The range [64Kb, 68Kb[ is used for the primary superblock of the filesystem.
  $XFS_IO_PROG -c "pwrite -S 0xfd 0 64K" $SCRATCH_DEV | _filter_xfs_io
  $XFS_IO_PROG -c "pwrite -S 0xfd 68K 956K" $SCRATCH_DEV | _filter_xfs_io

  # Now mount the filesystem and perform a fitrim against it.
  _scratch_mount
  _require_batched_discard $SCRATCH_MNT
  $FSTRIM_PROG $SCRATCH_MNT

  # Now unmount the filesystem and verify the content of the ranges was not
  # modified (no trim/discard happened on them).
  _scratch_unmount
  echo "Content of the ranges [0, 64Kb] and [68Kb, 1Mb[ after fitrim:"
  od -t x1 -N $((64 * 1024)) $SCRATCH_DEV
  od -t x1 -j $((68 * 1024)) -N $((956 * 1024)) $SCRATCH_DEV

  status=0
  exit
Reported-by: NVincent Petry  <PVince81@yahoo.fr>
Reported-by: NAndrei Borzenkov <arvidjaar@gmail.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=109341
Fixes: 499f377f (btrfs: iterate over unused chunk space in FITRIM)
Cc: stable@vger.kernel.org # 4.3+
Signed-off-by: NFilipe Manana <fdmanana@suse.com>
      8cdc7c5b