When inserting a key range item (BTRFS_DIR_LOG_INDEX_KEY) while logging
a directory, we don't expect the insertion to fail with -EEXIST, because
we are holding the directory's log_mutex and we have dropped all existing
BTRFS_DIR_LOG_INDEX_KEY keys from the log tree before we started to log
the directory. However it's possible that during the logging we attempt
to insert the same BTRFS_DIR_LOG_INDEX_KEY key twice, but for this to
happen we need to race with insertions of items from other inodes in the
subvolume's tree while we are logging a directory. Here's how this can
happen:

1) We are logging a directory with inode number 1000 that has its items
   spread across 3 leaves in the subvolume's tree:

   leaf A - has index keys from the range 2 to 20 for example. The last
   item in the leaf corresponds to a dir item for index number 20. All
   these dir items were created in a past transaction.

   leaf B - has index keys from the range 22 to 100 for example. It has
   no keys from other inodes, all its keys are dir index keys for our
   directory inode number 1000. Its first key is for the dir item with
   a sequence number of 22. All these dir items were also created in a
   past transaction.

   leaf C - has index keys for our directory for the range 101 to 120 for
   example. This leaf also has items from other inodes, and its first
   item corresponds to the dir item for index number 101 for our directory
   with inode number 1000;

2) When we finish processing the items from leaf A at log_dir_items(),
   we log a BTRFS_DIR_LOG_INDEX_KEY key with an offset of 21 and a last
   offset of 21, meaning the log is authoritative for the index range
   from 21 to 21 (a single sequence number). At this point leaf B was
   not yet modified in the current transaction;

3) When we return from log_dir_items() we have released our read lock on
   leaf B, and have set *last_offset_ret to 21 (index number of the first
   item on leaf B minus 1);

4) Some other task inserts an item for other inode (inode number 1001 for
   example) into leaf C. That resulted in pushing some items from leaf C
   into leaf B, in order to make room for the new item, so now leaf B
   has dir index keys for the sequence number range from 22 to 102 and
   leaf C has the dir items for the sequence number range 103 to 120;

5) At log_directory_changes() we call log_dir_items() again, passing it
   a 'min_offset' / 'min_key' value of 22 (*last_offset_ret from step 3
   plus 1, so 21 + 1). Then btrfs_search_forward() leaves us at slot 0
   of leaf B, since leaf B was modified in the current transaction.

   We have also initialized 'last_old_dentry_offset' to 20 after calling
   btrfs_previous_item() at log_dir_items(), as it left us at the last
   item of leaf A, which refers to the dir item with sequence number 20;

6) We then call process_dir_items_leaf() to process the dir items of
   leaf B, and when we process the first item, corresponding to slot 0,
   sequence number 22, we notice the dir item was created in a past
   transaction and its sequence number is greater than the value of
   *last_old_dentry_offset + 1 (20 + 1), so we decide to log again a
   BTRFS_DIR_LOG_INDEX_KEY key with an offset of 21 and an end range
   of 21 (key.offset - 1 == 22 - 1 == 21), which results in an -EEXIST
   error from insert_dir_log_key(), as we have already inserted that
   key at step 2, triggering the assertion at process_dir_items_leaf().

The trace produced in dmesg is like the following:

assertion failed: ret != -EEXIST, in fs/btrfs/tree-log.c:3857
[198255.980839][ T7460] ------------[ cut here ]------------
[198255.981666][ T7460] kernel BUG at fs/btrfs/ctree.h:3617!
[198255.983141][ T7460] invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI
[198255.984080][ T7460] CPU: 0 PID: 7460 Comm: repro-ghost-dir Not tainted 5.18.0-5314c78ac373-misc-next+
[198255.986027][ T7460] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
[198255.988600][ T7460] RIP: 0010:assertfail.constprop.0+0x1c/0x1e
[198255.989465][ T7460] Code: 8b 4c 89 (...)
[198255.992599][ T7460] RSP: 0018:ffffc90007387188 EFLAGS: 00010282
[198255.993414][ T7460] RAX: 000000000000003d RBX: 0000000000000065 RCX: 0000000000000000
[198255.996056][ T7460] RDX: 0000000000000001 RSI: ffffffff8b62b180 RDI: fffff52000e70e24
[198255.997668][ T7460] RBP: ffffc90007387188 R08: 000000000000003d R09: ffff8881f0e16507
[198255.999199][ T7460] R10: ffffed103e1c2ca0 R11: 0000000000000001 R12: 00000000ffffffef
[198256.000683][ T7460] R13: ffff88813befc630 R14: ffff888116c16e70 R15: ffffc90007387358
[198256.007082][ T7460] FS:  00007fc7f7c24640(0000) GS:ffff8881f0c00000(0000) knlGS:0000000000000000
[198256.009939][ T7460] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[198256.014133][ T7460] CR2: 0000560bb16d0b78 CR3: 0000000140b34005 CR4: 0000000000170ef0
[198256.015239][ T7460] Call Trace:
[198256.015674][ T7460]  <TASK>
[198256.016313][ T7460]  log_dir_items.cold+0x16/0x2c
[198256.018858][ T7460]  ? replay_one_extent+0xbf0/0xbf0
[198256.025932][ T7460]  ? release_extent_buffer+0x1d2/0x270
[198256.029658][ T7460]  ? rcu_read_lock_sched_held+0x16/0x80
[198256.031114][ T7460]  ? lock_acquired+0xbe/0x660
[198256.032633][ T7460]  ? rcu_read_lock_sched_held+0x16/0x80
[198256.034386][ T7460]  ? lock_release+0xcf/0x8a0
[198256.036152][ T7460]  log_directory_changes+0xf9/0x170
[198256.036993][ T7460]  ? log_dir_items+0xba0/0xba0
[198256.037661][ T7460]  ? do_raw_write_unlock+0x7d/0xe0
[198256.038680][ T7460]  btrfs_log_inode+0x233b/0x26d0
[198256.041294][ T7460]  ? log_directory_changes+0x170/0x170
[198256.042864][ T7460]  ? btrfs_attach_transaction_barrier+0x60/0x60
[198256.045130][ T7460]  ? rcu_read_lock_sched_held+0x16/0x80
[198256.046568][ T7460]  ? lock_release+0xcf/0x8a0
[198256.047504][ T7460]  ? lock_downgrade+0x420/0x420
[198256.048712][ T7460]  ? ilookup5_nowait+0x81/0xa0
[198256.049747][ T7460]  ? lock_downgrade+0x420/0x420
[198256.050652][ T7460]  ? do_raw_spin_unlock+0xa9/0x100
[198256.051618][ T7460]  ? __might_resched+0x128/0x1c0
[198256.052511][ T7460]  ? __might_sleep+0x66/0xc0
[198256.053442][ T7460]  ? __kasan_check_read+0x11/0x20
[198256.054251][ T7460]  ? iget5_locked+0xbd/0x150
[198256.054986][ T7460]  ? run_delayed_iput_locked+0x110/0x110
[198256.055929][ T7460]  ? btrfs_iget+0xc7/0x150
[198256.056630][ T7460]  ? btrfs_orphan_cleanup+0x4a0/0x4a0
[198256.057502][ T7460]  ? free_extent_buffer+0x13/0x20
[198256.058322][ T7460]  btrfs_log_inode+0x2654/0x26d0
[198256.059137][ T7460]  ? log_directory_changes+0x170/0x170
[198256.060020][ T7460]  ? rcu_read_lock_sched_held+0x16/0x80
[198256.060930][ T7460]  ? rcu_read_lock_sched_held+0x16/0x80
[198256.061905][ T7460]  ? lock_contended+0x770/0x770
[198256.062682][ T7460]  ? btrfs_log_inode_parent+0xd04/0x1750
[198256.063582][ T7460]  ? lock_downgrade+0x420/0x420
[198256.064432][ T7460]  ? preempt_count_sub+0x18/0xc0
[198256.065550][ T7460]  ? __mutex_lock+0x580/0xdc0
[198256.066654][ T7460]  ? stack_trace_save+0x94/0xc0
[198256.068008][ T7460]  ? __kasan_check_write+0x14/0x20
[198256.072149][ T7460]  ? __mutex_unlock_slowpath+0x12a/0x430
[198256.073145][ T7460]  ? mutex_lock_io_nested+0xcd0/0xcd0
[198256.074341][ T7460]  ? wait_for_completion_io_timeout+0x20/0x20
[198256.075345][ T7460]  ? lock_downgrade+0x420/0x420
[198256.076142][ T7460]  ? lock_contended+0x770/0x770
[198256.076939][ T7460]  ? do_raw_spin_lock+0x1c0/0x1c0
[198256.078401][ T7460]  ? btrfs_sync_file+0x5e6/0xa40
[198256.080598][ T7460]  btrfs_log_inode_parent+0x523/0x1750
[198256.081991][ T7460]  ? wait_current_trans+0xc8/0x240
[198256.083320][ T7460]  ? lock_downgrade+0x420/0x420
[198256.085450][ T7460]  ? btrfs_end_log_trans+0x70/0x70
[198256.086362][ T7460]  ? rcu_read_lock_sched_held+0x16/0x80
[198256.087544][ T7460]  ? lock_release+0xcf/0x8a0
[198256.088305][ T7460]  ? lock_downgrade+0x420/0x420
[198256.090375][ T7460]  ? dget_parent+0x8e/0x300
[198256.093538][ T7460]  ? do_raw_spin_lock+0x1c0/0x1c0
[198256.094918][ T7460]  ? lock_downgrade+0x420/0x420
[198256.097815][ T7460]  ? do_raw_spin_unlock+0xa9/0x100
[198256.101822][ T7460]  ? dget_parent+0xb7/0x300
[198256.103345][ T7460]  btrfs_log_dentry_safe+0x48/0x60
[198256.105052][ T7460]  btrfs_sync_file+0x629/0xa40
[198256.106829][ T7460]  ? start_ordered_ops.constprop.0+0x120/0x120
[198256.109655][ T7460]  ? __fget_files+0x161/0x230
[198256.110760][ T7460]  vfs_fsync_range+0x6d/0x110
[198256.111923][ T7460]  ? start_ordered_ops.constprop.0+0x120/0x120
[198256.113556][ T7460]  __x64_sys_fsync+0x45/0x70
[198256.114323][ T7460]  do_syscall_64+0x5c/0xc0
[198256.115084][ T7460]  ? syscall_exit_to_user_mode+0x3b/0x50
[198256.116030][ T7460]  ? do_syscall_64+0x69/0xc0
[198256.116768][ T7460]  ? do_syscall_64+0x69/0xc0
[198256.117555][ T7460]  ? do_syscall_64+0x69/0xc0
[198256.118324][ T7460]  ? sysvec_call_function_single+0x57/0xc0
[198256.119308][ T7460]  ? asm_sysvec_call_function_single+0xa/0x20
[198256.120363][ T7460]  entry_SYSCALL_64_after_hwframe+0x44/0xae
[198256.121334][ T7460] RIP: 0033:0x7fc7fe97b6ab
[198256.122067][ T7460] Code: 0f 05 48 (...)
[198256.125198][ T7460] RSP: 002b:00007fc7f7c23950 EFLAGS: 00000293 ORIG_RAX: 000000000000004a
[198256.126568][ T7460] RAX: ffffffffffffffda RBX: 00007fc7f7c239f0 RCX: 00007fc7fe97b6ab
[198256.127942][ T7460] RDX: 0000000000000002 RSI: 000056167536bcf0 RDI: 0000000000000004
[198256.129302][ T7460] RBP: 0000000000000004 R08: 0000000000000000 R09: 000000007ffffeb8
[198256.130670][ T7460] R10: 00000000000001ff R11: 0000000000000293 R12: 0000000000000001
[198256.132046][ T7460] R13: 0000561674ca8140 R14: 00007fc7f7c239d0 R15: 000056167536dab8
[198256.133403][ T7460]  </TASK>

Fix this by treating -EEXIST as expected at insert_dir_log_key() and have
it update the item with an end offset corresponding to the maximum between
the previously logged end offset and the new requested end offset. The end
offsets may be different due to dir index key deletions that happened as
part of unlink operations while we are logging a directory (triggered when
fsyncing some other inode parented by the directory) or during renames
which always attempt to log a single dir index deletion.
Reported-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org>
Link: https://lore.kernel.org/linux-btrfs/YmyefE9mc2xl5ZMz@hungrycats.org/
Fixes: 732d591a ("btrfs: stop copying old dir items when logging a directory")
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>