Currently, scrub_missing_raid56_worker() puts and potentially frees
sblock (which embeds the work item) and then submits a bio through
scrub_wr_submit(). This is another potential instance of the bug in
"btrfs: don't prematurely free work in run_ordered_work()". Fix it by
dropping the reference after we submit the bio.
Reviewed-by: NJohannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: NOmar Sandoval <osandov@fb.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

This is prep work for moving all of the block group cache code into its
own file.
Signed-off-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
[ minor comment updates ]
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Preparatory patch for additional RAID1 profiles with more copies. The
mask will contain 3-copy and 4-copy, most of the checks for plain RAID1
work the same for the other profiles.
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Currently btrfs_csum_data() relied on the crc32c() wrapper around the
crypto framework for calculating the CRCs.

As we have our own crypto_shash structure in the fs_info now, we can
directly call into the crypto framework without going trough the wrapper.

This way we can even remove the btrfs_csum_data() and btrfs_csum_final()
wrappers.

The module dependency on crc32c is preserved via MODULE_SOFTDEP("pre:
crc32c"), which was previously provided by LIBCRC32C config option doing
the same.
Signed-off-by: NJohannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

BTRFS has the implicit assumption that a checksum in btrfs_orderd_sums
is 4 bytes. While this is true for CRC32C, it is not for any other
checksum.

Change the data type to be a byte array and adjust loop index
calculation accordingly.

This includes moving the adjustment of 'index' by 'ins_size' in
btrfs_csum_file_blocks() before dividing 'ins_size' by the checksum
size, because before this patch the 'sums' member of 'struct
btrfs_ordered_sum' was 4 Bytes in size and afterwards it is only one
byte.
Reviewed-by: NNikolay Borisov <nborisov@suse.com>
Signed-off-by: NJohannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

There are several places that call nr_data_stripes, but this value does
not change.
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs_info::mapping_tree is the physical<->logical mapping tree and uses
the same underlying structure as extents, but is embedded to another
structure. There are no other members and this indirection is useless.
No functional change.
Signed-off-by: NDavid Sterba <dsterba@suse.com>

We can read fs_info from the device and can drop it from the parameters.
Signed-off-by: NDavid Sterba <dsterba@suse.com>

The error code used here is wrong as it's not invalid to try to start
scrub when umount has begun.  Returning EAGAIN is more user friendly as
it's recoverable.
Signed-off-by: NDavid Sterba <dsterba@suse.com>

The scrub_ctx csum_list member must be initialized before scrub_free_ctx
is called. If the csum_list is not initialized beforehand, the
list_empty call in scrub_free_csums will result in a null deref if the
allocation fails in the for loop.

Fixes: a2de733c ("btrfs: scrub")
CC: stable@vger.kernel.org # 3.0+
Reviewed-by: NNikolay Borisov <nborisov@suse.com>
Signed-off-by: NDan Robertson <dan@dlrobertson.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

The scrub worker pointers are not NULL iff the scrub is running, so
reset them back once the last reference is dropped. Add assertions to
the initial phase of scrub to verify that.
Reviewed-by: NAnand Jain <anand.jain@oracle.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Use the refcount_t for fs_info::scrub_workers_refcnt instead of int so
we get the extra checks. All reference changes are still done under
scrub_lock.
Signed-off-by: NAnand Jain <anand.jain@oracle.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

scrub_workers_refcnt is protected by scrub_lock, add lockdep_assert_held()
in scrub_workers_get().
Signed-off-by: NAnand Jain <anand.jain@oracle.com>
Suggested-by: NNikolay Borisov <nborisov@suse.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

This fixes a longstanding lockdep warning triggered by
fstests/btrfs/011.

Circular locking dependency check reports warning[1], that's because the
btrfs_scrub_dev() calls the stack #0 below with, the fs_info::scrub_lock
held. The test case leading to this warning:

  $ mkfs.btrfs -f /dev/sdb
  $ mount /dev/sdb /btrfs
  $ btrfs scrub start -B /btrfs

In fact we have fs_info::scrub_workers_refcnt to track if the init and destroy
of the scrub workers are needed. So once we have incremented and decremented
the fs_info::scrub_workers_refcnt value in the thread, its ok to drop the
scrub_lock, and then actually do the btrfs_destroy_workqueue() part. So this
patch drops the scrub_lock before calling btrfs_destroy_workqueue().

  [359.258534] ======================================================
  [359.260305] WARNING: possible circular locking dependency detected
  [359.261938] 5.0.0-rc6-default #461 Not tainted
  [359.263135] ------------------------------------------------------
  [359.264672] btrfs/20975 is trying to acquire lock:
  [359.265927] 00000000d4d32bea ((wq_completion)"%s-%s""btrfs", name){+.+.}, at: flush_workqueue+0x87/0x540
  [359.268416]
  [359.268416] but task is already holding lock:
  [359.270061] 0000000053ea26a6 (&fs_info->scrub_lock){+.+.}, at: btrfs_scrub_dev+0x322/0x590 [btrfs]
  [359.272418]
  [359.272418] which lock already depends on the new lock.
  [359.272418]
  [359.274692]
  [359.274692] the existing dependency chain (in reverse order) is:
  [359.276671]
  [359.276671] -> #3 (&fs_info->scrub_lock){+.+.}:
  [359.278187]        __mutex_lock+0x86/0x9c0
  [359.279086]        btrfs_scrub_pause+0x31/0x100 [btrfs]
  [359.280421]        btrfs_commit_transaction+0x1e4/0x9e0 [btrfs]
  [359.281931]        close_ctree+0x30b/0x350 [btrfs]
  [359.283208]        generic_shutdown_super+0x64/0x100
  [359.284516]        kill_anon_super+0x14/0x30
  [359.285658]        btrfs_kill_super+0x12/0xa0 [btrfs]
  [359.286964]        deactivate_locked_super+0x29/0x60
  [359.288242]        cleanup_mnt+0x3b/0x70
  [359.289310]        task_work_run+0x98/0xc0
  [359.290428]        exit_to_usermode_loop+0x83/0x90
  [359.291445]        do_syscall_64+0x15b/0x180
  [359.292598]        entry_SYSCALL_64_after_hwframe+0x49/0xbe
  [359.294011]
  [359.294011] -> #2 (sb_internal#2){.+.+}:
  [359.295432]        __sb_start_write+0x113/0x1d0
  [359.296394]        start_transaction+0x369/0x500 [btrfs]
  [359.297471]        btrfs_finish_ordered_io+0x2aa/0x7c0 [btrfs]
  [359.298629]        normal_work_helper+0xcd/0x530 [btrfs]
  [359.299698]        process_one_work+0x246/0x610
  [359.300898]        worker_thread+0x3c/0x390
  [359.302020]        kthread+0x116/0x130
  [359.303053]        ret_from_fork+0x24/0x30
  [359.304152]
  [359.304152] -> #1 ((work_completion)(&work->normal_work)){+.+.}:
  [359.306100]        process_one_work+0x21f/0x610
  [359.307302]        worker_thread+0x3c/0x390
  [359.308465]        kthread+0x116/0x130
  [359.309357]        ret_from_fork+0x24/0x30
  [359.310229]
  [359.310229] -> #0 ((wq_completion)"%s-%s""btrfs", name){+.+.}:
  [359.311812]        lock_acquire+0x90/0x180
  [359.312929]        flush_workqueue+0xaa/0x540
  [359.313845]        drain_workqueue+0xa1/0x180
  [359.314761]        destroy_workqueue+0x17/0x240
  [359.315754]        btrfs_destroy_workqueue+0x57/0x200 [btrfs]
  [359.317245]        scrub_workers_put+0x2c/0x60 [btrfs]
  [359.318585]        btrfs_scrub_dev+0x336/0x590 [btrfs]
  [359.319944]        btrfs_dev_replace_by_ioctl.cold.19+0x179/0x1bb [btrfs]
  [359.321622]        btrfs_ioctl+0x28a4/0x2e40 [btrfs]
  [359.322908]        do_vfs_ioctl+0xa2/0x6d0
  [359.324021]        ksys_ioctl+0x3a/0x70
  [359.325066]        __x64_sys_ioctl+0x16/0x20
  [359.326236]        do_syscall_64+0x54/0x180
  [359.327379]        entry_SYSCALL_64_after_hwframe+0x49/0xbe
  [359.328772]
  [359.328772] other info that might help us debug this:
  [359.328772]
  [359.330990] Chain exists of:
  [359.330990]   (wq_completion)"%s-%s""btrfs", name --> sb_internal#2 --> &fs_info->scrub_lock
  [359.330990]
  [359.334376]  Possible unsafe locking scenario:
  [359.334376]
  [359.336020]        CPU0                    CPU1
  [359.337070]        ----                    ----
  [359.337821]   lock(&fs_info->scrub_lock);
  [359.338506]                                lock(sb_internal#2);
  [359.339506]                                lock(&fs_info->scrub_lock);
  [359.341461]   lock((wq_completion)"%s-%s""btrfs", name);
  [359.342437]
  [359.342437]  *** DEADLOCK ***
  [359.342437]
  [359.343745] 1 lock held by btrfs/20975:
  [359.344788]  #0: 0000000053ea26a6 (&fs_info->scrub_lock){+.+.}, at: btrfs_scrub_dev+0x322/0x590 [btrfs]
  [359.346778]
  [359.346778] stack backtrace:
  [359.347897] CPU: 0 PID: 20975 Comm: btrfs Not tainted 5.0.0-rc6-default #461
  [359.348983] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.11.2-0-gf9626cc-prebuilt.qemu-project.org 04/01/2014
  [359.350501] Call Trace:
  [359.350931]  dump_stack+0x67/0x90
  [359.351676]  print_circular_bug.isra.37.cold.56+0x15c/0x195
  [359.353569]  check_prev_add.constprop.44+0x4f9/0x750
  [359.354849]  ? check_prev_add.constprop.44+0x286/0x750
  [359.356505]  __lock_acquire+0xb84/0xf10
  [359.357505]  lock_acquire+0x90/0x180
  [359.358271]  ? flush_workqueue+0x87/0x540
  [359.359098]  flush_workqueue+0xaa/0x540
  [359.359912]  ? flush_workqueue+0x87/0x540
  [359.360740]  ? drain_workqueue+0x1e/0x180
  [359.361565]  ? drain_workqueue+0xa1/0x180
  [359.362391]  drain_workqueue+0xa1/0x180
  [359.363193]  destroy_workqueue+0x17/0x240
  [359.364539]  btrfs_destroy_workqueue+0x57/0x200 [btrfs]
  [359.365673]  scrub_workers_put+0x2c/0x60 [btrfs]
  [359.366618]  btrfs_scrub_dev+0x336/0x590 [btrfs]
  [359.367594]  ? start_transaction+0xa1/0x500 [btrfs]
  [359.368679]  btrfs_dev_replace_by_ioctl.cold.19+0x179/0x1bb [btrfs]
  [359.369545]  btrfs_ioctl+0x28a4/0x2e40 [btrfs]
  [359.370186]  ? __lock_acquire+0x263/0xf10
  [359.370777]  ? kvm_clock_read+0x14/0x30
  [359.371392]  ? kvm_sched_clock_read+0x5/0x10
  [359.372248]  ? sched_clock+0x5/0x10
  [359.372786]  ? sched_clock_cpu+0xc/0xc0
  [359.373662]  ? do_vfs_ioctl+0xa2/0x6d0
  [359.374552]  do_vfs_ioctl+0xa2/0x6d0
  [359.375378]  ? do_sigaction+0xff/0x250
  [359.376233]  ksys_ioctl+0x3a/0x70
  [359.376954]  __x64_sys_ioctl+0x16/0x20
  [359.377772]  do_syscall_64+0x54/0x180
  [359.378841]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
  [359.380422] RIP: 0033:0x7f5429296a97

Backporting to older kernels: scrub_nocow_workers must be freed the same
way as the others.

CC: stable@vger.kernel.org # 4.4+
Signed-off-by: NAnand Jain <anand.jain@oracle.com>
[ update changelog ]
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

The kernel log messages help debugging and audit, add them for scrub
Signed-off-by: NAnand Jain <anand.jain@oracle.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Both btrfs_find_device() and find_device() does the same thing except
that the latter does not take the seed device onto account in the device
scanning context. We can merge them.
Signed-off-by: NAnand Jain <anand.jain@oracle.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

btrfs_find_device() accepts fs_info as an argument and retrieves
fs_devices from fs_info.

Instead use fs_devices, so that this function can be used in non-mount
(during device scanning) context as well.
Signed-off-by: NAnand Jain <anand.jain@oracle.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

The typos accumulate over time so once in a while time they get fixed in
a large patch.
Signed-off-by: NAndrea Gelmini <andrea.gelmini@gelma.net>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Since scrub workers only do memory allocation with GFP_KERNEL when they
need to perform repair, we can move the recent setup of the nofs context
up to scrub_handle_errored_block() instead of setting it up down the call
chain at insert_full_stripe_lock() and scrub_add_page_to_wr_bio(),
removing some duplicate code and comment. So the only paths for which a
scrub worker can do memory allocations using GFP_KERNEL are the following:

 scrub_bio_end_io_worker()
   scrub_block_complete()
     scrub_handle_errored_block()
       lock_full_stripe()
         insert_full_stripe_lock()
           -> kmalloc with GFP_KERNEL

  scrub_bio_end_io_worker()
    scrub_block_complete()
      scrub_handle_errored_block()
        scrub_write_page_to_dev_replace()
          scrub_add_page_to_wr_bio()
            -> kzalloc with GFP_KERNEL
Signed-off-by: NFilipe Manana <fdmanana@suse.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

The scrub context is allocated with GFP_KERNEL and called from
btrfs_scrub_dev under the fs_info::device_list_mutex. This is not safe
regarding reclaim that could try to flush filesystem data in order to
get the memory. And the device_list_mutex is held during superblock
commit, so this would cause a lockup.

Move the alocation and initialization before any changes that require
the mutex.
Signed-off-by: NDavid Sterba <dsterba@suse.com>

We can pass fs_info directly as this is the only member of btrfs_device
that's bing used inside scrub_setup_ctx.
Reviewed-by: NNikolay Borisov <nborisov@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

The dev-replace locking functions are now trivial wrappers around rw
semaphore that can be used directly everywhere. No functional change.
Signed-off-by: NDavid Sterba <dsterba@suse.com>

When a transaction commit starts, it attempts to pause scrub and it blocks
until the scrub is paused. So while the transaction is blocked waiting for
scrub to pause, we can not do memory allocation with GFP_KERNEL from scrub,
otherwise we risk getting into a deadlock with reclaim.

Checking for scrub pause requests is done early at the beginning of the
while loop of scrub_stripe() and later in the loop, scrub_extent() and
scrub_raid56_parity() are called, which in turn call scrub_pages() and
scrub_pages_for_parity() respectively. These last two functions do memory
allocations using GFP_KERNEL. Same problem could happen while scrubbing
the super blocks, since it calls scrub_pages().

We also can not have any of the worker tasks, created by the scrub task,
doing GFP_KERNEL allocations, because before pausing, the scrub task waits
for all the worker tasks to complete (also done at scrub_stripe()).

So make sure GFP_NOFS is used for the memory allocations because at any
time a scrub pause request can happen from another task that started to
commit a transaction.

Fixes: 58c4e173 ("btrfs: scrub: use GFP_KERNEL on the submission path")
CC: stable@vger.kernel.org # 4.6+
Reviewed-by: NNikolay Borisov <nborisov@suse.com>
Signed-off-by: NFilipe Manana <fdmanana@suse.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

The wrapper is too trivial, open coding does not make it less readable.
Reviewed-by: NOmar Sandoval <osandov@fb.com>
Reviewed-by: NAnand Jain <anand.jain@oracle.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

struct scrub_ctx has an ->is_dev_replace member, so there's no point in
passing around is_dev_replace where sctx is available.
Signed-off-by: NOmar Sandoval <osandov@fb.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Cleanup patch and no functional changes.
Signed-off-by: NMisono Tomohiro <misono.tomohiro@jp.fujitsu.com>
Reviewed-by: NQu Wenruo <wqu@suse.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Remove the remaining code that misused the page cache pages during
device replace and could cause data corruption for compressed nodatasum
extents. Such files do not normally exist but there's a bug that allows
this combination and the corruption was exposed by device replace fixup
code.
Signed-off-by: NQu Wenruo <wqu@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Introduce a small helper, btrfs_mark_bg_unused(), to acquire locks and
add a block group to unused_bgs list.

No functional modification, and only 3 callers are involved.
Signed-off-by: NQu Wenruo <wqu@suse.com>
Reviewed-by: NNikolay Borisov <nborisov@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

The helper is trivial and marked as deprecated.
Signed-off-by: NDavid Sterba <dsterba@suse.com>

It can be referenced from the passed bg cache.
Signed-off-by: NNikolay Borisov <nborisov@suse.com>
Reviewed-by: NQu Wenruo <wqu@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Since commit ac0b4145 ("btrfs: scrub: Don't use inode pages
for device replace") the function is not used and we can remove all
functions down the call chain.

There was an optimization that reused inode pages to speed up device
replace, but broke when there was nodatasum and compressed page. The
potential performance gain is small so we don't loose much by removing
it and using scrub_pages same as the other pages.
Signed-off-by: NQu Wenruo <wqu@suse.com>
[ update changelog ]
Signed-off-by: NDavid Sterba <dsterba@suse.com>

In commit ac0b4145 ("btrfs: scrub: Don't use inode pages for device
replace") we removed the branch of copy_nocow_pages() to avoid
corruption for compressed nodatasum extents.

However above commit only solves the problem in scrub_extent(), if
during scrub_pages() we failed to read some pages,
sctx->no_io_error_seen will be non-zero and we go to fixup function
scrub_handle_errored_block().

In scrub_handle_errored_block(), for sctx without csum (no matter if
we're doing replace or scrub) we go to scrub_fixup_nodatasum() routine,
which does the similar thing with copy_nocow_pages(), but does it
without the extra check in copy_nocow_pages() routine.

So for test cases like btrfs/100, where we emulate read errors during
replace/scrub, we could corrupt compressed extent data again.

This patch will fix it just by avoiding any "optimization" for
nodatasum, just falls back to the normal fixup routine by try read from
any good copy.

This also solves WARN_ON() or dead lock caused by lame backref iteration
in scrub_fixup_nodatasum() routine.

The deadlock or WARN_ON() won't be triggered before commit ac0b4145
("btrfs: scrub: Don't use inode pages for device replace") since
copy_nocow_pages() have better locking and extra check for data extent,
and it's already doing the fixup work by try to read data from any good
copy, so it won't go scrub_fixup_nodatasum() anyway.

This patch disables the faulty code and will be removed completely in a
followup patch.

Fixes: ac0b4145 ("btrfs: scrub: Don't use inode pages for device replace")
Signed-off-by: NQu Wenruo <wqu@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

[BUG]
Btrfs can create compressed extent without checksum (even though it
shouldn't), and if we then try to replace device containing such extent,
the result device will contain all the uncompressed data instead of the
compressed one.

Test case already submitted to fstests:
https://patchwork.kernel.org/patch/10442353/

[CAUSE]
When handling compressed extent without checksum, device replace will
goe into copy_nocow_pages() function.

In that function, btrfs will get all inodes referring to this data
extents and then use find_or_create_page() to get pages direct from that
inode.

The problem here is, pages directly from inode are always uncompressed.
And for compressed data extent, they mismatch with on-disk data.
Thus this leads to corrupted compressed data extent written to replace
device.

[FIX]
In this attempt, we could just remove the "optimization" branch, and let
unified scrub_pages() to handle it.

Although scrub_pages() won't bother reusing page cache, it will be a
little slower, but it does the correct csum checking and won't cause
such data corruption caused by "optimization".

Note about the fix: this is the minimal fix that can be backported to
older stable trees without conflicts. The whole callchain from
copy_nocow_pages() can be deleted, and will be in followup patches.

Fixes: ff023aac ("Btrfs: add code to scrub to copy read data to another disk")
CC: stable@vger.kernel.org # 4.4+
Reported-by: NJames Harvey <jamespharvey20@gmail.com>
Reviewed-by: NJames Harvey <jamespharvey20@gmail.com>
Signed-off-by: NQu Wenruo <wqu@suse.com>
[ remove code removal, add note why ]
Signed-off-by: NDavid Sterba <dsterba@suse.com>

This patch will add the following trace events:
1) btrfs_remove_block_group
   For btrfs_remove_block_group() function.
   Triggered when a block group is really removed.

2) btrfs_add_unused_block_group
   Triggered which block group is added to unused_bgs list.

3) btrfs_skip_unused_block_group
   Triggered which unused block group is not deleted.

These trace events is pretty handy to debug case related to block group
auto remove.
Signed-off-by: NQu Wenruo <wqu@suse.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Remove GPL boilerplate text (long, short, one-line) and keep the rest,
ie. personal, company or original source copyright statements. Add the
SPDX header.
Signed-off-by: NDavid Sterba <dsterba@suse.com>

The current calls are unclear in what way btrfs_dev_replace_lock takes
the locks, so drop the argument, split the helpers and use similar
naming as for read and write locks.
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Using lockdep_assert_held is preferred, replace mutex_is_locked.
Signed-off-by: NDavid Sterba <dsterba@suse.com>

Added in b5d67f64 ("Btrfs: change scrub to support big blocks") but
rendered redundant by be50a8dd ("Btrfs: Simplify
scrub_setup_recheck_block()'s argument").
Signed-off-by: NNikolay Borisov <nborisov@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

In case of raid56, writes and rebuilds always take BTRFS_STRIPE_LEN(64K)
as unit, however, scrub_extent() sets blocksize as unit, so rebuild
process may be triggered on every block on a same stripe.

A typical example would be that when we're replacing a disappeared disk,
all reads on the disks get -EIO, every block (size is 4K if blocksize is
4K) would go thru these,

scrub_handle_errored_block
  scrub_recheck_block # re-read pages one by one
  scrub_recheck_block # rebuild by calling raid56_parity_recover()
                        page by page

Although with raid56 stripe cache most of reads during rebuild can be
avoided, the parity recover calculation(xor or raid6 algorithms) needs to
be done $(BTRFS_STRIPE_LEN / blocksize) times.

This makes it smarter by doing raid56 scrub/replace on stripe length.
Signed-off-by: NLiu Bo <bo.li.liu@oracle.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

In the last step of scrub_handle_error_block, we try to combine good
copies on all possible mirrors, this works fine for raid1 and raid10,
but not for raid56 as it's doing parity rebuild.

If parity rebuild doesn't get back with correct data which matches its
checksum, in case of replace we'd rather write what is stored in the
source device than the data calculuated from parity.
Signed-off-by: NLiu Bo <bo.li.liu@oracle.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>