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From: Thorsten Leemhuis <>
To: Zygo Blaxell <>,
	Thorsten Leemhuis <>
Cc: Josef Bacik <>,
	Nikolay Borisov <>,
	linux-btrfs <>,
	"" <>
Subject: Re: bisected: btrfs dedupe regression in v5.11-rc1
Date: Fri, 18 Feb 2022 15:46:26 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Hi, this is your Linux kernel regression tracker speaking. Top-posting
for once, to make this easy accessible to everyone.

What's up here? Can anyone (Zygo? Josef?) please provide a status
update? Yes, it took quite a while till this regression got found, but
nevertheless this looks to take awfully long to get resolved for a
regression was bisected weeks ago.

Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)

P.S.: As the Linux kernel's regression tracker I'm getting a lot of
reports on my table. I can only look briefly into most of them and lack
knowledge about most of the areas they concern. I thus unfortunately
will sometimes get things wrong or miss something important. I hope
that's not the case here; if you think it is, don't hesitate to tell me
in a public reply, it's in everyone's interest to set the public record

On 21.01.22 01:27, Zygo Blaxell wrote:
> On Thu, Jan 20, 2022 at 03:04:19PM +0100, Thorsten Leemhuis wrote:
>> Hi, this is your Linux kernel regression tracker speaking.
>> On 07.01.22 19:31, Zygo Blaxell wrote:
>>> On Fri, Dec 17, 2021 at 03:50:44PM -0500, Zygo Blaxell wrote:
>>> I left my VM running tests for a few weeks and got some more information.
>>> Or at least more data, I'm not feeling particularly informed by it.  :-P
>>> 1.  It's not a regression.  5.10 has the same symptoms, but about 100x
>>> less often (once a week under these test conditions, compared to once
>>> every 90 minutes or so on 5.11-rc1).
>> Well, I'd still call it a regression, as it's now happening way more
>> often and thus will likely hit more users. It's thus a bit like a
>> problem that leads to higher energy consumption: things still work, but
>> worse than before -- nevertheless it's considered a regression. Anway:
>> What's the status here? Are you still investigating the issue? Are any
>> developers looking out for the root cause?
> I think Josef's plan (start inside the logical_ino ioctl with bpftrace
> and work upwards to see where the looping is getting stuck) is a good plan,
> but due to conflicting priorities I haven't found the time to act on it.
> I can take experimental patches and throw them at my repro setup if
> anyone would like to supply some.
>> Ciao, Thorsten
>> P.S.: As a Linux kernel regression tracker I'm getting a lot of reports
>> on my table. I can only look briefly into most of them. Unfortunately
>> therefore I sometimes will get things wrong or miss something important.
>> I hope that's not the case here; if you think it is, don't hesitate to
>> tell me about it in a public reply, that's in everyone's interest.
>> BTW, I have no personal interest in this issue, which is tracked using
>> regzbot, my Linux kernel regression tracking bot
>> ( I'm only posting
>> this mail to get things rolling again and hence don't need to be CC on
>> all further activities wrt to this regression.
>> #regzbot poke
>>> 2.  Bisection doesn't work, because there are patches that are repeatably
>>> good and bad mixed together, so the bisect algorithm (even with stochastic
>>> enhancement) repeatably picks the wrong commits and converges with
>>> high confidence on nonsense.  Instead of bisecting, I picked commits
>>> semi-randomly from 5.11-rc1's patch set, and got these results:
>>>    124  3a160a933111 btrfs: drop never met disk total bytes check in verify_one_dev_extent
>>> 	1x hang, 2x slower
>>>    125  bacce86ae8a7 btrfs: drop unused argument step from btrfs_free_extra_devids
>>> 	1x pass (fast)
>>>    126  2766ff61762c btrfs: update the number of bytes used by an inode atomically
>>> 	1x hang (<20 minutes)
>>>    127  7f458a3873ae btrfs: fix race when defragmenting leads to unnecessary IO
>>> 	1x hang, runs 3x slower
>>>    128  5893dfb98f25 btrfs: refactor btrfs_drop_extents() to make it easier to extend
>>> 	2x hang (<20 minutes)
>>>    129  e114c545bb69 btrfs: set the lockdep class for extent buffers on creation
>>> 	2x pass (but runs 2x slower, both times)
>>>    130  3fbaf25817f7 btrfs: pass the owner_root and level to alloc_extent_buffer
>>> 	1x pass
>>>    131  5d81230baa90 btrfs: pass the root owner and level around for readahead
>>> 	1x pass
>>>    132  1b7ec85ef490 btrfs: pass root owner to read_tree_block
>>> 	1x pass
>>>    133  182c79fcb857 btrfs: use btrfs_read_node_slot in btrfs_qgroup_trace_subtree
>>>    134  3acfbd6a990c btrfs: use btrfs_read_node_slot in qgroup_trace_new_subtree_blocks
>>> 	1x hang
>>>    135  6b2cb7cb959a btrfs: use btrfs_read_node_slot in qgroup_trace_extent_swap
>>>    136  c990ada2a0bb btrfs: use btrfs_read_node_slot in walk_down_tree
>>> 	1x hang
>>>    137  6b3426be27de btrfs: use btrfs_read_node_slot in replace_path
>>> 	1x hang, 1x pass
>>>    138  c975253682e0 btrfs: use btrfs_read_node_slot in do_relocation
>>> 	1x hang
>>>    139  8ef385bbf099 btrfs: use btrfs_read_node_slot in walk_down_reloc_tree
>>> 	1x hang, 1x pass
>>>    140  206983b72a36 btrfs: use btrfs_read_node_slot in btrfs_realloc_node
>>> 	1x pass
>>>    141  bfb484d922a3 btrfs: cleanup extent buffer readahead
>>> 	1x pass
>>>    142  416e3445ef80 btrfs: remove lockdep classes for the fs tree
>>>    143  3e48d8d2540d btrfs: discard: reschedule work after sysfs param update
>>>    144  df903e5d294f btrfs: don't miss async discards after scheduled work override
>>>    145  6e88f116bd4c btrfs: discard: store async discard delay as ns not as jiffies
>>> 	2x hang
>>>    146  e50404a8a699 btrfs: discard: speed up async discard up to iops_limit
>>>    [snip]
>>>    155  0d01e247a06b btrfs: assert page mapping lock in attach_extent_buffer_page
>>> 	1x hang, 1x pass
>>>    156  bbb86a371791 btrfs: protect fs_info->caching_block_groups by block_group_cache_lock
>>> 	1x hang
>>>    157  e747853cae3a btrfs: load free space cache asynchronously
>>> 	1x pass
>>>    158  4d7240f0abda btrfs: load the free space cache inode extents from commit root
>>> 	1x hang
>>>    159  cd79909bc7cd btrfs: load free space cache into a temporary ctl
>>> 	2x pass
>>>    160  66b53bae46c8 btrfs: cleanup btrfs_discard_update_discardable usage
>>> 	2x hang, 1x pass
>>>    161  2ca08c56e813 btrfs: explicitly protect ->last_byte_to_unpin in unpin_extent_range
>>> 	2x pass
>>>    162  27d56e62e474 btrfs: update last_byte_to_unpin in switch_commit_roots
>>> 	2x pass
>>>    163  9076dbd5ee83 btrfs: do not shorten unpin len for caching block groups
>>>    164  dc5161648693 btrfs: reorder extent buffer members for better packing
>>> 	2x pass
>>>    165  b9729ce014f6 btrfs: locking: rip out path->leave_spinning
>>>    166  ac5887c8e013 btrfs: locking: remove all the blocking helpers
>>>    167  2ae0c2d80d25 btrfs: scrub: remove local copy of csum_size from context
>>>    168  419b791ce760 btrfs: check integrity: remove local copy of csum_size
>>> 	1x hang, 1x pass
>>>    169  713cebfb9891 btrfs: remove unnecessary local variables for checksum size
>>>    170  223486c27b36 btrfs: switch cached fs_info::csum_size from u16 to u32
>>>    171  55fc29bed8dd btrfs: use cached value of fs_info::csum_size everywhere
>>>    172  fe5ecbe818de btrfs: precalculate checksums per leaf once
>>>    173  22b6331d9617 btrfs: store precalculated csum_size in fs_info
>>>    174  265fdfa6ce0a btrfs: replace s_blocksize_bits with fs_info::sectorsize_bits
>>>    175  098e63082b9b btrfs: replace div_u64 by shift in free_space_bitmap_size
>>> 	2x pass
>>>    176  ab108d992b12 btrfs: use precalculated sectorsize_bits from fs_info
>>>    [snip]
>>>    200  5e8b9ef30392 btrfs: move pos increment and pagecache extension to btrfs_buffered_write
>>> 	1x pass
>>>    201  4e4cabece9f9 btrfs: split btrfs_direct_IO to read and write
>>>    [snip]
>>>    215  d70bf7484f72 btrfs: unify the ro checking for mount options
>>> 	1x pass
>>>    216  a6889caf6ec6 btrfs: do not start readahead for csum tree when scrubbing non-data block groups
>>>    217  a57ad681f12e btrfs: assert we are holding the reada_lock when releasing a readahead zone
>>>    218  aa8c1a41a1e6 btrfs: set EXTENT_NORESERVE bits side btrfs_dirty_pages()
>>>    219  13f0dd8f7861 btrfs: use round_down while calculating start position in btrfs_dirty_pages()
>>>    220  949b32732eab btrfs: use iosize while reading compressed pages
>>>    221  eefa45f59379 btrfs: calculate num_pages, reserve_bytes once in btrfs_buffered_write
>>>    222  fb8a7e941b1b btrfs: calculate more accurate remaining time to sleep in transaction_kthread
>>> 	1x pass
>>> There is some repeatability in these results--some commits have a much
>>> lower failure rate than others--but I don't see a reason why the bad
>>> commits are bad or the good commits are good.  There are some commits with
>>> locking and concurrency implications, but they're as likely to produce
>>> good as bad results in test.  Sometimes there's a consistent change in
>>> test result after a commit that only rearranges function arguments on
>>> the stack.
>>> Maybe what we're looking at is a subtle race that is popping up due
>>> to unrelated changes in the kernel, and disappearing just as often,
>>> and 5.11-rc1 in particular did something innocent that aggravates
>>> it somehow, so all later kernels hit the problem more often than
>>> 5.10 did.
>>> 3.  Somewhere around "7f458a3873ae btrfs: fix race when defragmenting
>>> leads to unnecessary IO" bees starts running about 3x slower than on
>>> earlier kernels.  bees is a nightmare of nondeterministically racing
>>> worker threads, so I'm not sure how important this observation is,
>>> but it keeps showing up in the data.
>>> 4.  I had one machine on 5.10.84 (not a test VM) with a shell process
>>> that got stuck spinning 100% CPU in the kernel on sys_write.  bees was
>>> also running, but its threads were all stuck waiting for the shell to
>>> release the transaction.  Other crashes on 5.10.8x kernels look more
>>> like the one in this thread, with a logical_ino spinning.
>>>>> If it's not looping there, it may be looping higher up, but I don't see where it
>>>>> would be doing that.  Lets start here and work our way up if we need to.
>>>>> Thanks,

  parent reply	other threads:[~2022-02-18 14:46 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-10 18:34 bisected: btrfs dedupe regression in v5.11-rc1: 3078d85c9a10 vfs: verify source area in vfs_dedupe_file_range_one() Zygo Blaxell
2021-12-12 10:03 ` Thorsten Leemhuis
2021-12-13 13:28 ` Nikolay Borisov
2021-12-13 23:12   ` Zygo Blaxell
2021-12-14 11:11     ` Nikolay Borisov
2021-12-14 19:50       ` Zygo Blaxell
2021-12-14 22:25         ` Nikolay Borisov
2021-12-16  5:33           ` Zygo Blaxell
2021-12-16 21:29             ` Nikolay Borisov
2021-12-16 22:07               ` Josef Bacik
2021-12-17 20:50                 ` Zygo Blaxell
2022-01-07 18:31                   ` bisected: btrfs dedupe regression in v5.11-rc1 Zygo Blaxell
2022-01-20 14:04                     ` Thorsten Leemhuis
2022-01-21  0:27                       ` Zygo Blaxell
2022-02-09 12:22                         ` Libor Klepáč
2022-02-18 14:46                         ` Thorsten Leemhuis [this message]
2022-03-06 10:31                           ` Thorsten Leemhuis
2022-03-06 23:34                             ` Zygo Blaxell
2022-03-07  6:17                               ` Thorsten Leemhuis
2021-12-17  5:38               ` bisected: btrfs dedupe regression in v5.11-rc1: 3078d85c9a10 vfs: verify source area in vfs_dedupe_file_range_one() Zygo Blaxell
2022-06-13  8:38 ` Libor Klepáč
2022-06-21  5:08   ` Zygo Blaxell

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