linux-toradex.git/fs/btrfs/send.c, branch v5.15

btrfs: allocate backref_ctx on stack in find_extent_clone

2021-08-23T11:19:10+00:00

Instead of using kmalloc() to allocate backref_ctx, allocate backref_ctx
on stack. The size is reasonably small.

sizeof(backref_ctx) = 48

Reviewed-by: Anand Jain 
Signed-off-by: Goldwyn Rodrigues 
Signed-off-by: David Sterba

btrfs: constify and cleanup variables in comparators

2021-08-23T11:19:03+00:00

Comparators just read the data and thus get const parameters. This
should be also preserved by the local variables, update all comparators
passed to sort or bsearch.

Cleanups:

- unnecessary casts are dropped
- btrfs_cmp_device_free_bytes is cleaned up to follow the common pattern
  and 'inline' is dropped as the function address is taken

Signed-off-by: David Sterba

btrfs: send: fix crash when memory allocations trigger reclaim

2021-06-22T12:11:58+00:00

When doing a send we don't expect the task to ever start a transaction
after the initial check that verifies if commit roots match the regular
roots. This is because after that we set current->journal_info with a
stub (special value) that signals we are in send context, so that we take
a read lock on an extent buffer when reading it from disk and verifying
it is valid (its generation matches the generation stored in the parent).
This stub was introduced in 2014 by commit a26e8c9f75b0bf ("Btrfs: don't
clear uptodate if the eb is under IO") in order to fix a concurrency issue
between send and balance.

However there is one particular exception where we end up needing to start
a transaction and when this happens it results in a crash with a stack
trace like the following:

[60015.902283] kernel: WARNING: CPU: 3 PID: 58159 at arch/x86/include/asm/kfence.h:44 kfence_protect_page+0x21/0x80
[60015.902292] kernel: Modules linked in: uinput rfcomm snd_seq_dummy (...)
[60015.902384] kernel: CPU: 3 PID: 58159 Comm: btrfs Not tainted 5.12.9-300.fc34.x86_64 #1
[60015.902387] kernel: Hardware name: Gigabyte Technology Co., Ltd. To be filled by O.E.M./F2A88XN-WIFI, BIOS F6 12/24/2015
[60015.902389] kernel: RIP: 0010:kfence_protect_page+0x21/0x80
[60015.902393] kernel: Code: ff 0f 1f 84 00 00 00 00 00 55 48 89 fd (...)
[60015.902396] kernel: RSP: 0018:ffff9fb583453220 EFLAGS: 00010246
[60015.902399] kernel: RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff9fb583453224
[60015.902401] kernel: RDX: ffff9fb583453224 RSI: 0000000000000000 RDI: 0000000000000000
[60015.902402] kernel: RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
[60015.902404] kernel: R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000002
[60015.902406] kernel: R13: ffff9fb583453348 R14: 0000000000000000 R15: 0000000000000001
[60015.902408] kernel: FS:  00007f158e62d8c0(0000) GS:ffff93bd37580000(0000) knlGS:0000000000000000
[60015.902410] kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[60015.902412] kernel: CR2: 0000000000000039 CR3: 00000001256d2000 CR4: 00000000000506e0
[60015.902414] kernel: Call Trace:
[60015.902419] kernel:  kfence_unprotect+0x13/0x30
[60015.902423] kernel:  page_fault_oops+0x89/0x270
[60015.902427] kernel:  ? search_module_extables+0xf/0x40
[60015.902431] kernel:  ? search_bpf_extables+0x57/0x70
[60015.902435] kernel:  kernelmode_fixup_or_oops+0xd6/0xf0
[60015.902437] kernel:  __bad_area_nosemaphore+0x142/0x180
[60015.902440] kernel:  exc_page_fault+0x67/0x150
[60015.902445] kernel:  asm_exc_page_fault+0x1e/0x30
[60015.902450] kernel: RIP: 0010:start_transaction+0x71/0x580
[60015.902454] kernel: Code: d3 0f 84 92 00 00 00 80 e7 06 0f 85 63 (...)
[60015.902456] kernel: RSP: 0018:ffff9fb5834533f8 EFLAGS: 00010246
[60015.902458] kernel: RAX: 0000000000000001 RBX: 0000000000000001 RCX: 0000000000000000
[60015.902460] kernel: RDX: 0000000000000801 RSI: 0000000000000000 RDI: 0000000000000039
[60015.902462] kernel: RBP: ffff93bc0a7eb800 R08: 0000000000000001 R09: 0000000000000000
[60015.902463] kernel: R10: 0000000000098a00 R11: 0000000000000001 R12: 0000000000000001
[60015.902464] kernel: R13: 0000000000000000 R14: ffff93bc0c92b000 R15: ffff93bc0c92b000
[60015.902468] kernel:  btrfs_commit_inode_delayed_inode+0x5d/0x120
[60015.902473] kernel:  btrfs_evict_inode+0x2c5/0x3f0
[60015.902476] kernel:  evict+0xd1/0x180
[60015.902480] kernel:  inode_lru_isolate+0xe7/0x180
[60015.902483] kernel:  __list_lru_walk_one+0x77/0x150
[60015.902487] kernel:  ? iput+0x1a0/0x1a0
[60015.902489] kernel:  ? iput+0x1a0/0x1a0
[60015.902491] kernel:  list_lru_walk_one+0x47/0x70
[60015.902495] kernel:  prune_icache_sb+0x39/0x50
[60015.902497] kernel:  super_cache_scan+0x161/0x1f0
[60015.902501] kernel:  do_shrink_slab+0x142/0x240
[60015.902505] kernel:  shrink_slab+0x164/0x280
[60015.902509] kernel:  shrink_node+0x2c8/0x6e0
[60015.902512] kernel:  do_try_to_free_pages+0xcb/0x4b0
[60015.902514] kernel:  try_to_free_pages+0xda/0x190
[60015.902516] kernel:  __alloc_pages_slowpath.constprop.0+0x373/0xcc0
[60015.902521] kernel:  ? __memcg_kmem_charge_page+0xc2/0x1e0
[60015.902525] kernel:  __alloc_pages_nodemask+0x30a/0x340
[60015.902528] kernel:  pipe_write+0x30b/0x5c0
[60015.902531] kernel:  ? set_next_entity+0xad/0x1e0
[60015.902534] kernel:  ? switch_mm_irqs_off+0x58/0x440
[60015.902538] kernel:  __kernel_write+0x13a/0x2b0
[60015.902541] kernel:  kernel_write+0x73/0x150
[60015.902543] kernel:  send_cmd+0x7b/0xd0
[60015.902545] kernel:  send_extent_data+0x5a3/0x6b0
[60015.902549] kernel:  process_extent+0x19b/0xed0
[60015.902551] kernel:  btrfs_ioctl_send+0x1434/0x17e0
[60015.902554] kernel:  ? _btrfs_ioctl_send+0xe1/0x100
[60015.902557] kernel:  _btrfs_ioctl_send+0xbf/0x100
[60015.902559] kernel:  ? enqueue_entity+0x18c/0x7b0
[60015.902562] kernel:  btrfs_ioctl+0x185f/0x2f80
[60015.902564] kernel:  ? psi_task_change+0x84/0xc0
[60015.902569] kernel:  ? _flat_send_IPI_mask+0x21/0x40
[60015.902572] kernel:  ? check_preempt_curr+0x2f/0x70
[60015.902576] kernel:  ? selinux_file_ioctl+0x137/0x1e0
[60015.902579] kernel:  ? expand_files+0x1cb/0x1d0
[60015.902582] kernel:  ? __x64_sys_ioctl+0x82/0xb0
[60015.902585] kernel:  __x64_sys_ioctl+0x82/0xb0
[60015.902588] kernel:  do_syscall_64+0x33/0x40
[60015.902591] kernel:  entry_SYSCALL_64_after_hwframe+0x44/0xae
[60015.902595] kernel: RIP: 0033:0x7f158e38f0ab
[60015.902599] kernel: Code: ff ff ff 85 c0 79 9b (...)
[60015.902602] kernel: RSP: 002b:00007ffcb2519bf8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[60015.902605] kernel: RAX: ffffffffffffffda RBX: 00007ffcb251ae00 RCX: 00007f158e38f0ab
[60015.902607] kernel: RDX: 00007ffcb2519cf0 RSI: 0000000040489426 RDI: 0000000000000004
[60015.902608] kernel: RBP: 0000000000000004 R08: 00007f158e297640 R09: 00007f158e297640
[60015.902610] kernel: R10: 0000000000000008 R11: 0000000000000246 R12: 0000000000000000
[60015.902612] kernel: R13: 0000000000000002 R14: 00007ffcb251aee0 R15: 0000558c1a83e2a0
[60015.902615] kernel: ---[ end trace 7bbc33e23bb887ae ]---

This happens because when writing to the pipe, by calling kernel_write(),
we end up doing page allocations using GFP_HIGHUSER | __GFP_ACCOUNT as the
gfp flags, which allow reclaim to happen if there is memory pressure. This
allocation happens at fs/pipe.c:pipe_write().

If the reclaim is triggered, inode eviction can be triggered and that in
turn can result in starting a transaction if the inode has a link count
of 0. The transaction start happens early on during eviction, when we call
btrfs_commit_inode_delayed_inode() at btrfs_evict_inode(). This happens if
there is currently an open file descriptor for an inode with a link count
of 0 and the reclaim task gets a reference on the inode before that
descriptor is closed, in which case the reclaim task ends up doing the
final iput that triggers the inode eviction.

When we have assertions enabled (CONFIG_BTRFS_ASSERT=y), this triggers
the following assertion at transaction.c:start_transaction():

    /* Send isn't supposed to start transactions. */
    ASSERT(current->journal_info != BTRFS_SEND_TRANS_STUB);

And when assertions are not enabled, it triggers a crash since after that
assertion we cast current->journal_info into a transaction handle pointer
and then dereference it:

   if (current->journal_info) {
       WARN_ON(type & TRANS_EXTWRITERS);
       h = current->journal_info;
       refcount_inc(&h->use_count);
       (...)

Which obviously results in a crash due to an invalid memory access.

The same type of issue can happen during other memory allocations we
do directly in the send code with kmalloc (and friends) as they use
GFP_KERNEL and therefore may trigger reclaim too, which started to
happen since 2016 after commit e780b0d1c1523e ("btrfs: send: use
GFP_KERNEL everywhere").

The issue could be solved by setting up a NOFS context for the entire
send operation so that reclaim could not be triggered when allocating
memory or pages through kernel_write(). However that is not very friendly
and we can in fact get rid of the send stub because:

1) The stub was introduced way back in 2014 by commit a26e8c9f75b0bf
   ("Btrfs: don't clear uptodate if the eb is under IO") to solve an
   issue exclusive to when send and balance are running in parallel,
   however there were other problems between balance and send and we do
   not allow anymore to have balance and send run concurrently since
   commit 9e967495e0e0ae ("Btrfs: prevent send failures and crashes due
   to concurrent relocation"). More generically the issues are between
   send and relocation, and that last commit eliminated only the
   possibility of having send and balance run concurrently, but shrinking
   a device also can trigger relocation, and on zoned filesystems we have
   relocation of partially used block groups triggered automatically as
   well. The previous patch that has a subject of:

   "btrfs: ensure relocation never runs while we have send operations running"

   Addresses all the remaining cases that can trigger relocation.

2) We can actually allow starting and even committing transactions while
   in a send context if needed because send is not holding any locks that
   would block the start or the commit of a transaction.

So get rid of all the logic added by commit a26e8c9f75b0bf ("Btrfs: don't
clear uptodate if the eb is under IO"). We can now always call
clear_extent_buffer_uptodate() at verify_parent_transid() since send is
the only case that uses commit roots without having a transaction open or
without holding the commit_root_sem.

Reported-by: Chris Murphy 
Link: https://lore.kernel.org/linux-btrfs/CAJCQCtRQ57=qXo3kygwpwEBOU_CA_eKvdmjP52sU=eFvuVOEGw@mail.gmail.com/
Signed-off-by: Filipe Manana 
Reviewed-by: David Sterba 
Signed-off-by: David Sterba

btrfs: ensure relocation never runs while we have send operations running

2021-06-22T12:11:58+00:00

Relocation and send do not play well together because while send is
running a block group can be relocated, a transaction committed and
the respective disk extents get re-allocated and written to or discarded
while send is about to do something with the extents.

This was explained in commit 9e967495e0e0ae ("Btrfs: prevent send failures
and crashes due to concurrent relocation"), which prevented balance and
send from running in parallel but it did not address one remaining case
where chunk relocation can happen: shrinking a device (and device deletion
which shrinks a device's size to 0 before deleting the device).

We also have now one more case where relocation is triggered: on zoned
filesystems partially used block groups get relocated by a background
thread, introduced in commit 18bb8bbf13c183 ("btrfs: zoned: automatically
reclaim zones").

So make sure that instead of preventing balance from running when there
are ongoing send operations, we prevent relocation from happening.
This uses the infrastructure recently added by a patch that has the
subject: "btrfs: add cancellable chunk relocation support".

Also it adds a spinlock used exclusively for the exclusivity between
send and relocation, as before fs_info->balance_mutex was used, which
would make an attempt to run send to block waiting for balance to
finish, which can take a lot of time on large filesystems.

Signed-off-by: Filipe Manana 
Reviewed-by: David Sterba 
Signed-off-by: David Sterba

btrfs: fix typos in comments

2021-06-22T12:11:57+00:00

Fix typos that have snuck in since the last round. Found by codespell.

Signed-off-by: David Sterba

btrfs: send: use list_move_tail instead of list_del/list_add_tail

2021-06-22T12:11:57+00:00

Use list_move_tail() instead of list_del() + list_add_tail() as it's
doing the same thing and allows further cleanups.  Open code
name_cache_used() as there is only one user.

Reported-by: Hulk Robot 
Signed-off-by: Baokun Li 
Reviewed-by: David Sterba 
Signed-off-by: David Sterba

btrfs: send: fix invalid path for unlink operations after parent orphanization

2021-06-22T12:11:57+00:00

During an incremental send operation, when processing the new references
for the current inode, we might send an unlink operation for another inode
that has a conflicting path and has more than one hard link. However this
path was computed and cached before we processed previous new references
for the current inode. We may have orphanized a directory of that path
while processing a previous new reference, in which case the path will
be invalid and cause the receiver process to fail.

The following reproducer triggers the problem and explains how/why it
happens in its comments:

  $ cat test-send-unlink.sh
  #!/bin/bash

  DEV=/dev/sdi
  MNT=/mnt/sdi

  mkfs.btrfs -f $DEV >/dev/null
  mount $DEV $MNT

  # Create our test files and directory. Inode 259 (file3) has two hard
  # links.
  touch $MNT/file1
  touch $MNT/file2
  touch $MNT/file3

  mkdir $MNT/A
  ln $MNT/file3 $MNT/A/hard_link

  # Filesystem looks like:
  #
  # .                                     (ino 256)
  # |----- file1                          (ino 257)
  # |----- file2                          (ino 258)
  # |----- file3                          (ino 259)
  # |----- A/                             (ino 260)
  #        |---- hard_link                (ino 259)
  #

  # Now create the base snapshot, which is going to be the parent snapshot
  # for a later incremental send.
  btrfs subvolume snapshot -r $MNT $MNT/snap1
  btrfs send -f /tmp/snap1.send $MNT/snap1

  # Move inode 257 into directory inode 260. This results in computing the
  # path for inode 260 as "/A" and caching it.
  mv $MNT/file1 $MNT/A/file1

  # Move inode 258 (file2) into directory inode 260, with a name of
  # "hard_link", moving first inode 259 away since it currently has that
  # location and name.
  mv $MNT/A/hard_link $MNT/tmp
  mv $MNT/file2 $MNT/A/hard_link

  # Now rename inode 260 to something else (B for example) and then create
  # a hard link for inode 258 that has the old name and location of inode
  # 260 ("/A").
  mv $MNT/A $MNT/B
  ln $MNT/B/hard_link $MNT/A

  # Filesystem now looks like:
  #
  # .                                     (ino 256)
  # |----- tmp                            (ino 259)
  # |----- file3                          (ino 259)
  # |----- B/                             (ino 260)
  # |      |---- file1                    (ino 257)
  # |      |---- hard_link                (ino 258)
  # |
  # |----- A                              (ino 258)

  # Create another snapshot of our subvolume and use it for an incremental
  # send.
  btrfs subvolume snapshot -r $MNT $MNT/snap2
  btrfs send -f /tmp/snap2.send -p $MNT/snap1 $MNT/snap2

  # Now unmount the filesystem, create a new one, mount it and try to
  # apply both send streams to recreate both snapshots.
  umount $DEV

  mkfs.btrfs -f $DEV >/dev/null

  mount $DEV $MNT

  # First add the first snapshot to the new filesystem by applying the
  # first send stream.
  btrfs receive -f /tmp/snap1.send $MNT

  # The incremental receive operation below used to fail with the
  # following error:
  #
  #    ERROR: unlink A/hard_link failed: No such file or directory
  #
  # This is because when send is processing inode 257, it generates the
  # path for inode 260 as "/A", since that inode is its parent in the send
  # snapshot, and caches that path.
  #
  # Later when processing inode 258, it first processes its new reference
  # that has the path of "/A", which results in orphanizing inode 260
  # because there is a a path collision. This results in issuing a rename
  # operation from "/A" to "/o260-6-0".
  #
  # Finally when processing the new reference "B/hard_link" for inode 258,
  # it notices that it collides with inode 259 (not yet processed, because
  # it has a higher inode number), since that inode has the name
  # "hard_link" under the directory inode 260. It also checks that inode
  # 259 has two hardlinks, so it decides to issue a unlink operation for
  # the name "hard_link" for inode 259. However the path passed to the
  # unlink operation is "/A/hard_link", which is incorrect since currently
  # "/A" does not exists, due to the orphanization of inode 260 mentioned
  # before. The path is incorrect because it was computed and cached
  # before the orphanization. This results in the receiver to fail with
  # the above error.
  btrfs receive -f /tmp/snap2.send $MNT

  umount $MNT

When running the test, it fails like this:

  $ ./test-send-unlink.sh
  Create a readonly snapshot of '/mnt/sdi' in '/mnt/sdi/snap1'
  At subvol /mnt/sdi/snap1
  Create a readonly snapshot of '/mnt/sdi' in '/mnt/sdi/snap2'
  At subvol /mnt/sdi/snap2
  At subvol snap1
  At snapshot snap2
  ERROR: unlink A/hard_link failed: No such file or directory

Fix this by recomputing a path before issuing an unlink operation when
processing the new references for the current inode if we previously
have orphanized a directory.

A test case for fstests will follow soon.

CC: stable@vger.kernel.org # 4.4+
Signed-off-by: Filipe Manana 
Signed-off-by: David Sterba

btrfs: fix deadlock when cloning inline extents and using qgroups

2021-04-28T18:09:47+00:00

There are a few exceptional cases where cloning an inline extent needs to
copy the inline extent data into a page of the destination inode.

When this happens, we end up starting a transaction while having a dirty
page for the destination inode and while having the range locked in the
destination's inode iotree too. Because when reserving metadata space
for a transaction we may need to flush existing delalloc in case there is
not enough free space, we have a mechanism in place to prevent a deadlock,
which was introduced in commit 3d45f221ce627d ("btrfs: fix deadlock when
cloning inline extent and low on free metadata space").

However when using qgroups, a transaction also reserves metadata qgroup
space, which can also result in flushing delalloc in case there is not
enough available space at the moment. When this happens we deadlock, since
flushing delalloc requires locking the file range in the inode's iotree
and the range was already locked at the very beginning of the clone
operation, before attempting to start the transaction.

When this issue happens, stack traces like the following are reported:

  [72747.556262] task:kworker/u81:9   state:D stack:    0 pid:  225 ppid:     2 flags:0x00004000
  [72747.556268] Workqueue: writeback wb_workfn (flush-btrfs-1142)
  [72747.556271] Call Trace:
  [72747.556273]  __schedule+0x296/0x760
  [72747.556277]  schedule+0x3c/0xa0
  [72747.556279]  io_schedule+0x12/0x40
  [72747.556284]  __lock_page+0x13c/0x280
  [72747.556287]  ? generic_file_readonly_mmap+0x70/0x70
  [72747.556325]  extent_write_cache_pages+0x22a/0x440 [btrfs]
  [72747.556331]  ? __set_page_dirty_nobuffers+0xe7/0x160
  [72747.556358]  ? set_extent_buffer_dirty+0x5e/0x80 [btrfs]
  [72747.556362]  ? update_group_capacity+0x25/0x210
  [72747.556366]  ? cpumask_next_and+0x1a/0x20
  [72747.556391]  extent_writepages+0x44/0xa0 [btrfs]
  [72747.556394]  do_writepages+0x41/0xd0
  [72747.556398]  __writeback_single_inode+0x39/0x2a0
  [72747.556403]  writeback_sb_inodes+0x1ea/0x440
  [72747.556407]  __writeback_inodes_wb+0x5f/0xc0
  [72747.556410]  wb_writeback+0x235/0x2b0
  [72747.556414]  ? get_nr_inodes+0x35/0x50
  [72747.556417]  wb_workfn+0x354/0x490
  [72747.556420]  ? newidle_balance+0x2c5/0x3e0
  [72747.556424]  process_one_work+0x1aa/0x340
  [72747.556426]  worker_thread+0x30/0x390
  [72747.556429]  ? create_worker+0x1a0/0x1a0
  [72747.556432]  kthread+0x116/0x130
  [72747.556435]  ? kthread_park+0x80/0x80
  [72747.556438]  ret_from_fork+0x1f/0x30

  [72747.566958] Workqueue: btrfs-flush_delalloc btrfs_work_helper [btrfs]
  [72747.566961] Call Trace:
  [72747.566964]  __schedule+0x296/0x760
  [72747.566968]  ? finish_wait+0x80/0x80
  [72747.566970]  schedule+0x3c/0xa0
  [72747.566995]  wait_extent_bit.constprop.68+0x13b/0x1c0 [btrfs]
  [72747.566999]  ? finish_wait+0x80/0x80
  [72747.567024]  lock_extent_bits+0x37/0x90 [btrfs]
  [72747.567047]  btrfs_invalidatepage+0x299/0x2c0 [btrfs]
  [72747.567051]  ? find_get_pages_range_tag+0x2cd/0x380
  [72747.567076]  __extent_writepage+0x203/0x320 [btrfs]
  [72747.567102]  extent_write_cache_pages+0x2bb/0x440 [btrfs]
  [72747.567106]  ? update_load_avg+0x7e/0x5f0
  [72747.567109]  ? enqueue_entity+0xf4/0x6f0
  [72747.567134]  extent_writepages+0x44/0xa0 [btrfs]
  [72747.567137]  ? enqueue_task_fair+0x93/0x6f0
  [72747.567140]  do_writepages+0x41/0xd0
  [72747.567144]  __filemap_fdatawrite_range+0xc7/0x100
  [72747.567167]  btrfs_run_delalloc_work+0x17/0x40 [btrfs]
  [72747.567195]  btrfs_work_helper+0xc2/0x300 [btrfs]
  [72747.567200]  process_one_work+0x1aa/0x340
  [72747.567202]  worker_thread+0x30/0x390
  [72747.567205]  ? create_worker+0x1a0/0x1a0
  [72747.567208]  kthread+0x116/0x130
  [72747.567211]  ? kthread_park+0x80/0x80
  [72747.567214]  ret_from_fork+0x1f/0x30

  [72747.569686] task:fsstress        state:D stack:    0 pid:841421 ppid:841417 flags:0x00000000
  [72747.569689] Call Trace:
  [72747.569691]  __schedule+0x296/0x760
  [72747.569694]  schedule+0x3c/0xa0
  [72747.569721]  try_flush_qgroup+0x95/0x140 [btrfs]
  [72747.569725]  ? finish_wait+0x80/0x80
  [72747.569753]  btrfs_qgroup_reserve_data+0x34/0x50 [btrfs]
  [72747.569781]  btrfs_check_data_free_space+0x5f/0xa0 [btrfs]
  [72747.569804]  btrfs_buffered_write+0x1f7/0x7f0 [btrfs]
  [72747.569810]  ? path_lookupat.isra.48+0x97/0x140
  [72747.569833]  btrfs_file_write_iter+0x81/0x410 [btrfs]
  [72747.569836]  ? __kmalloc+0x16a/0x2c0
  [72747.569839]  do_iter_readv_writev+0x160/0x1c0
  [72747.569843]  do_iter_write+0x80/0x1b0
  [72747.569847]  vfs_writev+0x84/0x140
  [72747.569869]  ? btrfs_file_llseek+0x38/0x270 [btrfs]
  [72747.569873]  do_writev+0x65/0x100
  [72747.569876]  do_syscall_64+0x33/0x40
  [72747.569879]  entry_SYSCALL_64_after_hwframe+0x44/0xa9

  [72747.569899] task:fsstress        state:D stack:    0 pid:841424 ppid:841417 flags:0x00004000
  [72747.569903] Call Trace:
  [72747.569906]  __schedule+0x296/0x760
  [72747.569909]  schedule+0x3c/0xa0
  [72747.569936]  try_flush_qgroup+0x95/0x140 [btrfs]
  [72747.569940]  ? finish_wait+0x80/0x80
  [72747.569967]  __btrfs_qgroup_reserve_meta+0x36/0x50 [btrfs]
  [72747.569989]  start_transaction+0x279/0x580 [btrfs]
  [72747.570014]  clone_copy_inline_extent+0x332/0x490 [btrfs]
  [72747.570041]  btrfs_clone+0x5b7/0x7a0 [btrfs]
  [72747.570068]  ? lock_extent_bits+0x64/0x90 [btrfs]
  [72747.570095]  btrfs_clone_files+0xfc/0x150 [btrfs]
  [72747.570122]  btrfs_remap_file_range+0x3d8/0x4a0 [btrfs]
  [72747.570126]  do_clone_file_range+0xed/0x200
  [72747.570131]  vfs_clone_file_range+0x37/0x110
  [72747.570134]  ioctl_file_clone+0x7d/0xb0
  [72747.570137]  do_vfs_ioctl+0x138/0x630
  [72747.570140]  __x64_sys_ioctl+0x62/0xc0
  [72747.570143]  do_syscall_64+0x33/0x40
  [72747.570146]  entry_SYSCALL_64_after_hwframe+0x44/0xa9

So fix this by skipping the flush of delalloc for an inode that is
flagged with BTRFS_INODE_NO_DELALLOC_FLUSH, meaning it is currently under
such a special case of cloning an inline extent, when flushing delalloc
during qgroup metadata reservation.

The special cases for cloning inline extents were added in kernel 5.7 by
by commit 05a5a7621ce66c ("Btrfs: implement full reflink support for
inline extents"), while having qgroup metadata space reservation flushing
delalloc when low on space was added in kernel 5.9 by commit
c53e9653605dbf ("btrfs: qgroup: try to flush qgroup space when we get
-EDQUOT"). So use a "Fixes:" tag for the later commit to ease stable
kernel backports.

Reported-by: Wang Yugui 
Link: https://lore.kernel.org/linux-btrfs/20210421083137.31E3.409509F4@e16-tech.com/
Fixes: c53e9653605dbf ("btrfs: qgroup: try to flush qgroup space when we get -EDQUOT")
CC: stable@vger.kernel.org # 5.9+
Reviewed-by: Qu Wenruo 
Signed-off-by: Filipe Manana 
Reviewed-by: David Sterba 
Signed-off-by: David Sterba

btrfs: improve btree readahead for full send operations

2021-04-19T15:25:17+00:00

Currently a full send operation uses the standard btree readahead when
iterating over the subvolume/snapshot btree, which despite bringing good
performance benefits, it could be improved in a few aspects for use cases
such as full send operations, which are guaranteed to visit every node
and leaf of a btree, in ascending and sequential order. The limitations
of that standard btree readahead implementation are the following:

1) It only triggers readahead for leaves that are physically close
   to the leaf being read, within a 64K range;

2) It only triggers readahead for the next or previous leaves if the
   leaf being read is not currently in memory;

3) It never triggers readahead for nodes.

So add a new readahead mode that addresses all these points and use it
for full send operations.

The following test script was used to measure the improvement on a box
using an average, consumer grade, spinning disk and with 16GiB of RAM:

  $ cat test.sh
  #!/bin/bash

  DEV=/dev/sdj
  MNT=/mnt/sdj
  MKFS_OPTIONS="--nodesize 16384"     # default, just to be explicit
  MOUNT_OPTIONS="-o max_inline=2048"  # default, just to be explicit

  mkfs.btrfs -f $MKFS_OPTIONS $DEV > /dev/null
  mount $MOUNT_OPTIONS $DEV $MNT

  # Create files with inline data to make it easier and faster to create
  # large btrees.
  add_files()
  {
      local total=$1
      local start_offset=$2
      local number_jobs=$3
      local total_per_job=$(($total / $number_jobs))

      echo "Creating $total new files using $number_jobs jobs"
      for ((n = 0; n < $number_jobs; n++)); do
          (
              local start_num=$(($start_offset + $n * $total_per_job))
              for ((i = 1; i <= $total_per_job; i++)); do
                  local file_num=$((start_num + $i))
                  local file_path="$MNT/file_${file_num}"
                  xfs_io -f -c "pwrite -S 0xab 0 2000" $file_path > /dev/null
                  if [ $? -ne 0 ]; then
                      echo "Failed creating file $file_path"
                      break
                  fi
              done
          ) &
          worker_pids[$n]=$!
      done

      wait ${worker_pids[@]}

      sync
      echo
      echo "btree node/leaf count: $(btrfs inspect-internal dump-tree -t 5 $DEV | egrep '^(node|leaf) ' | wc -l)"
  }

  initial_file_count=500000
  add_files $initial_file_count 0 4

  echo
  echo "Creating first snapshot..."
  btrfs subvolume snapshot -r $MNT $MNT/snap1

  echo
  echo "Adding more files..."
  add_files $((initial_file_count / 4)) $initial_file_count 4

  echo
  echo "Updating 1/50th of the initial files..."
  for ((i = 1; i < $initial_file_count; i += 50)); do
      xfs_io -c "pwrite -S 0xcd 0 20" $MNT/file_$i > /dev/null
  done

  echo
  echo "Creating second snapshot..."
  btrfs subvolume snapshot -r $MNT $MNT/snap2

  umount $MNT

  echo 3 > /proc/sys/vm/drop_caches
  blockdev --flushbufs $DEV &> /dev/null
  hdparm -F $DEV &> /dev/null

  mount $MOUNT_OPTIONS $DEV $MNT

  echo
  echo "Testing full send..."
  start=$(date +%s)
  btrfs send $MNT/snap1 > /dev/null
  end=$(date +%s)
  echo
  echo "Full send took $((end - start)) seconds"

  umount $MNT

The durations of the full send operation in seconds were the following:

Before this change:  217 seconds
After this change:   205 seconds (-5.7%)

Signed-off-by: Filipe Manana 
Signed-off-by: David Sterba

btrfs: add btree read ahead for incremental send operations

2021-04-19T15:25:15+00:00

Currently we do not do btree read ahead when doing an incremental send,
however we know that we will read and process any node or leaf in the
send root that has a generation greater than the generation of the parent
root. So triggering read ahead for such nodes and leafs is beneficial
for an incremental send.

This change does that, triggers read ahead of any node or leaf in the
send root that has a generation greater then the generation of the
parent root. As for the parent root, no readahead is triggered because
knowing in advance which nodes/leaves are going to be read is not so
linear and there's often a large time window between visiting nodes or
leaves of the parent root. So I opted to leave out the parent root,
and triggering read ahead for its nodes/leaves seemed to have not made
significant difference.

The following test script was used to measure the improvement on a box
using an average, consumer grade, spinning disk and with 16GiB of ram:

  $ cat test.sh
  #!/bin/bash

  DEV=/dev/sdj
  MNT=/mnt/sdj
  MKFS_OPTIONS="--nodesize 16384"     # default, just to be explicit
  MOUNT_OPTIONS="-o max_inline=2048"  # default, just to be explicit

  mkfs.btrfs -f $MKFS_OPTIONS $DEV > /dev/null
  mount $MOUNT_OPTIONS $DEV $MNT

  # Create files with inline data to make it easier and faster to create
  # large btrees.
  add_files()
  {
      local total=$1
      local start_offset=$2
      local number_jobs=$3
      local total_per_job=$(($total / $number_jobs))

      echo "Creating $total new files using $number_jobs jobs"
      for ((n = 0; n < $number_jobs; n++)); do
          (
              local start_num=$(($start_offset + $n * $total_per_job))
              for ((i = 1; i <= $total_per_job; i++)); do
                  local file_num=$((start_num + $i))
                  local file_path="$MNT/file_${file_num}"
                  xfs_io -f -c "pwrite -S 0xab 0 2000" $file_path > /dev/null
                  if [ $? -ne 0 ]; then
                      echo "Failed creating file $file_path"
                      break
                  fi
              done
          ) &
          worker_pids[$n]=$!
      done

      wait ${worker_pids[@]}

      sync
      echo
      echo "btree node/leaf count: $(btrfs inspect-internal dump-tree -t 5 $DEV | egrep '^(node|leaf) ' | wc -l)"
  }

  initial_file_count=500000
  add_files $initial_file_count 0 4

  echo
  echo "Creating first snapshot..."
  btrfs subvolume snapshot -r $MNT $MNT/snap1

  echo
  echo "Adding more files..."
  add_files $((initial_file_count / 4)) $initial_file_count 4

  echo
  echo "Updating 1/50th of the initial files..."
  for ((i = 1; i < $initial_file_count; i += 50)); do
      xfs_io -c "pwrite -S 0xcd 0 20" $MNT/file_$i > /dev/null
  done

  echo
  echo "Creating second snapshot..."
  btrfs subvolume snapshot -r $MNT $MNT/snap2

  umount $MNT

  echo 3 > /proc/sys/vm/drop_caches
  blockdev --flushbufs $DEV &> /dev/null
  hdparm -F $DEV &> /dev/null

  mount $MOUNT_OPTIONS $DEV $MNT

  echo
  echo "Testing full send..."
  start=$(date +%s)
  btrfs send $MNT/snap1 > /dev/null
  end=$(date +%s)
  echo
  echo "Full send took $((end - start)) seconds"

  umount $MNT

  echo 3 > /proc/sys/vm/drop_caches
  blockdev --flushbufs $DEV &> /dev/null
  hdparm -F $DEV &> /dev/null

  mount $MOUNT_OPTIONS $DEV $MNT

  echo
  echo "Testing incremental send..."
  start=$(date +%s)
  btrfs send -p $MNT/snap1 $MNT/snap2 > /dev/null
  end=$(date +%s)
  echo
  echo "Incremental send took $((end - start)) seconds"

  umount $MNT

Before this change, incremental send duration:

  with $initial_file_count == 200000:  51 seconds
  with $initial_file_count == 500000: 168 seconds

After this change, incremental send duration:

  with $initial_file_count == 200000:   39 seconds (-26.7%)
  with $initial_file_count == 500000:  125 seconds (-29.4%)

For $initial_file_count == 200000 there are 62600 nodes and leaves in the
btree of the first snapshot, and 77759 nodes and leaves in the btree of
the second snapshot. The root nodes were at level 2.

While for $initial_file_count == 500000 there are 152476 nodes and leaves
in the btree of the first snapshot, and 190511 nodes and leaves in the
btree of the second snapshot. The root nodes were at level 2 as well.

Signed-off-by: Filipe Manana 
Reviewed-by: David Sterba 
Signed-off-by: David Sterba