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12148367d7
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Boris Burkov 12148367d7 btrfs: fix potential dead lock in size class loading logic 
As reported by Filipe, there's a potential deadlock caused by
using btrfs_search_forward on commit_root. The locking there is
unconditional, even if ->skip_locking and ->search_commit_root is set.
It's not meant to be used for commit roots, so it always needs to do
locking.

So if another task is COWing a child node of the same root node and
then needs to wait for block group caching to complete when trying to
allocate a metadata extent, it deadlocks.

For example:

[539604.239315] sysrq: Show Blocked State
[539604.240133] task:kworker/u16:6   state:D stack:0     pid:2119594 ppid:2      flags:0x00004000
[539604.241613] Workqueue: btrfs-cache btrfs_work_helper [btrfs]
[539604.242673] Call Trace:
[539604.243129]  <TASK>
[539604.243925]  __schedule+0x41d/0xee0
[539604.244797]  ? rcu_read_lock_sched_held+0x12/0x70
[539604.245399]  ? rwsem_down_read_slowpath+0x185/0x490
[539604.246111]  schedule+0x5d/0xf0
[539604.246593]  rwsem_down_read_slowpath+0x2da/0x490
[539604.247290]  ? rcu_barrier_tasks_trace+0x10/0x20
[539604.248090]  __down_read_common+0x3d/0x150
[539604.248702]  down_read_nested+0xc3/0x140
[539604.249280]  __btrfs_tree_read_lock+0x24/0x100 [btrfs]
[539604.250097]  btrfs_read_lock_root_node+0x48/0x60 [btrfs]
[539604.250915]  btrfs_search_forward+0x59/0x460 [btrfs]
[539604.251781]  ? btrfs_global_root+0x50/0x70 [btrfs]
[539604.252476]  caching_thread+0x1be/0x920 [btrfs]
[539604.253167]  btrfs_work_helper+0xf6/0x400 [btrfs]
[539604.253848]  process_one_work+0x24f/0x5a0
[539604.254476]  worker_thread+0x52/0x3b0
[539604.255166]  ? __pfx_worker_thread+0x10/0x10
[539604.256047]  kthread+0xf0/0x120
[539604.256591]  ? __pfx_kthread+0x10/0x10
[539604.257212]  ret_from_fork+0x29/0x50
[539604.257822]  </TASK>
[539604.258233] task:btrfs-transacti state:D stack:0     pid:2236474 ppid:2      flags:0x00004000
[539604.259802] Call Trace:
[539604.260243]  <TASK>
[539604.260615]  __schedule+0x41d/0xee0
[539604.261205]  ? rcu_read_lock_sched_held+0x12/0x70
[539604.262000]  ? rwsem_down_read_slowpath+0x185/0x490
[539604.262822]  schedule+0x5d/0xf0
[539604.263374]  rwsem_down_read_slowpath+0x2da/0x490
[539604.266228]  ? lock_acquire+0x160/0x310
[539604.266917]  ? rcu_read_lock_sched_held+0x12/0x70
[539604.267996]  ? lock_contended+0x19e/0x500
[539604.268720]  __down_read_common+0x3d/0x150
[539604.269400]  down_read_nested+0xc3/0x140
[539604.270057]  __btrfs_tree_read_lock+0x24/0x100 [btrfs]
[539604.271129]  btrfs_read_lock_root_node+0x48/0x60 [btrfs]
[539604.272372]  btrfs_search_slot+0x143/0xf70 [btrfs]
[539604.273295]  update_block_group_item+0x9e/0x190 [btrfs]
[539604.274282]  btrfs_start_dirty_block_groups+0x1c4/0x4f0 [btrfs]
[539604.275381]  ? __mutex_unlock_slowpath+0x45/0x280
[539604.276390]  btrfs_commit_transaction+0xee/0xed0 [btrfs]
[539604.277391]  ? lock_acquire+0x1a4/0x310
[539604.278080]  ? start_transaction+0xcb/0x6c0 [btrfs]
[539604.279099]  transaction_kthread+0x142/0x1c0 [btrfs]
[539604.279996]  ? __pfx_transaction_kthread+0x10/0x10 [btrfs]
[539604.280673]  kthread+0xf0/0x120
[539604.281050]  ? __pfx_kthread+0x10/0x10
[539604.281496]  ret_from_fork+0x29/0x50
[539604.281966]  </TASK>
[539604.282255] task:fsstress        state:D stack:0     pid:2236483 ppid:1      flags:0x00004006
[539604.283897] Call Trace:
[539604.284700]  <TASK>
[539604.285088]  __schedule+0x41d/0xee0
[539604.285660]  schedule+0x5d/0xf0
[539604.286175]  btrfs_wait_block_group_cache_progress+0xf2/0x170 [btrfs]
[539604.287342]  ? __pfx_autoremove_wake_function+0x10/0x10
[539604.288450]  find_free_extent+0xd93/0x1750 [btrfs]
[539604.289256]  ? _raw_spin_unlock+0x29/0x50
[539604.289911]  ? btrfs_get_alloc_profile+0x127/0x2a0 [btrfs]
[539604.290843]  btrfs_reserve_extent+0x147/0x290 [btrfs]
[539604.291943]  btrfs_alloc_tree_block+0xcb/0x3e0 [btrfs]
[539604.292903]  __btrfs_cow_block+0x138/0x580 [btrfs]
[539604.293773]  btrfs_cow_block+0x10e/0x240 [btrfs]
[539604.294595]  btrfs_search_slot+0x7f3/0xf70 [btrfs]
[539604.295585]  btrfs_update_device+0x71/0x1b0 [btrfs]
[539604.296459]  btrfs_chunk_alloc_add_chunk_item+0xe0/0x340 [btrfs]
[539604.297489]  btrfs_chunk_alloc+0x1bf/0x490 [btrfs]
[539604.298335]  find_free_extent+0x6fa/0x1750 [btrfs]
[539604.299174]  ? _raw_spin_unlock+0x29/0x50
[539604.299950]  ? btrfs_get_alloc_profile+0x127/0x2a0 [btrfs]
[539604.300918]  btrfs_reserve_extent+0x147/0x290 [btrfs]
[539604.301797]  btrfs_alloc_tree_block+0xcb/0x3e0 [btrfs]
[539604.303017]  ? lock_release+0x224/0x4a0
[539604.303855]  __btrfs_cow_block+0x138/0x580 [btrfs]
[539604.304789]  btrfs_cow_block+0x10e/0x240 [btrfs]
[539604.305611]  btrfs_search_slot+0x7f3/0xf70 [btrfs]
[539604.306682]  ? btrfs_global_root+0x50/0x70 [btrfs]
[539604.308198]  lookup_inline_extent_backref+0x17b/0x7a0 [btrfs]
[539604.309254]  lookup_extent_backref+0x43/0xd0 [btrfs]
[539604.310122]  __btrfs_free_extent+0xf8/0x810 [btrfs]
[539604.310874]  ? lock_release+0x224/0x4a0
[539604.311724]  ? btrfs_merge_delayed_refs+0x17b/0x1d0 [btrfs]
[539604.313023]  __btrfs_run_delayed_refs+0x2ba/0x1260 [btrfs]
[539604.314271]  btrfs_run_delayed_refs+0x8f/0x1c0 [btrfs]
[539604.315445]  ? rcu_read_lock_sched_held+0x12/0x70
[539604.316706]  btrfs_commit_transaction+0xa2/0xed0 [btrfs]
[539604.317855]  ? do_raw_spin_unlock+0x4b/0xa0
[539604.318544]  ? _raw_spin_unlock+0x29/0x50
[539604.319240]  create_subvol+0x53d/0x6e0 [btrfs]
[539604.320283]  btrfs_mksubvol+0x4f5/0x590 [btrfs]
[539604.321220]  __btrfs_ioctl_snap_create+0x11b/0x180 [btrfs]
[539604.322307]  btrfs_ioctl_snap_create_v2+0xc6/0x150 [btrfs]
[539604.323295]  btrfs_ioctl+0x9f7/0x33e0 [btrfs]
[539604.324331]  ? rcu_read_lock_sched_held+0x12/0x70
[539604.325137]  ? lock_release+0x224/0x4a0
[539604.325808]  ? __x64_sys_ioctl+0x87/0xc0
[539604.326467]  __x64_sys_ioctl+0x87/0xc0
[539604.327109]  do_syscall_64+0x38/0x90
[539604.327875]  entry_SYSCALL_64_after_hwframe+0x72/0xdc
[539604.328792] RIP: 0033:0x7f05a7babaeb

This needs to use regular btrfs_search_slot() with some skip and stop
logic.

Since we only consider five samples (five search slots), don't bother
with the complexity of looking for commit_root_sem contention. If
necessary, it can be added to the load function in between samples.

Reported-by: Filipe Manana <fdmanana@kernel.org>
Link: https://lore.kernel.org/linux-btrfs/CAL3q7H7eKMD44Z1+=Kb-1RFMMeZpAm2fwyO59yeBwCcSOU80Pg@mail.gmail.com/
Fixes: c7eec3d9aa ("btrfs: load block group size class when caching")
Signed-off-by: Boris Burkov <boris@bur.io>
Signed-off-by: David Sterba <dsterba@suse.com>
2023-03-06 19:28:19 +01:00
arch powerpc fixes for 6.2 #5 2023-02-12 11:08:15 -08:00
block block: export bio_split_rw 2023-02-15 19:38:50 +01:00
certs certs: Fix build error when PKCS#11 URI contains semicolon 2023-01-31 17:53:01 +09:00
crypto This update includes the following changes: 2022-12-14 12:31:09 -08:00
Documentation Networking fixes for 6.2-rc8, including fixes from can and 2023-02-09 09:17:38 -08:00
drivers USB fixes for 6.2-rc8 2023-02-12 11:18:57 -08:00
fs btrfs: fix potential dead lock in size class loading logic 2023-03-06 19:28:19 +01:00
include iomap: remove IOMAP_F_ZONE_APPEND 2023-02-15 19:38:53 +01:00
init Kbuild fixes for v6.2 (3rd) 2023-01-21 10:56:37 -08:00
io_uring io_uring: always prep_async for drain requests 2023-01-27 06:29:29 -07:00
ipc Non-MM patches for 6.2-rc1. 2022-12-12 17:28:58 -08:00
kernel tracing: Fix showing of TASK_COMM_LEN instead of its value 2023-02-12 13:52:17 -08:00
lib - Lock the proper critical section when dealing with perf event context 2023-02-05 11:03:56 -08:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm Fix page corruption caused by racy check in __free_pages 2023-02-12 10:30:05 -08:00
net rds: rds_rm_zerocopy_callback() use list_first_entry() 2023-02-09 10:37:26 +01:00
rust rust: print: avoid evaluating arguments in pr_* macros in unsafe blocks 2023-01-16 00:54:35 +01:00
samples ftrace: Export ftrace_free_filter() to modules 2023-01-24 11:20:58 -05:00
scripts Kbuild fixes for v6.2 (4th) 2023-02-04 11:30:23 -08:00
security tomoyo: Update website link 2023-01-13 23:11:38 +09:00
sound sound fixes for 6.2-rc8 2023-02-10 08:37:48 -08:00
tools Revert "mm: Always release pages to the buddy allocator in memblock_free_late()." 2023-02-11 10:51:45 -08:00
usr usr/gen_init_cpio.c: remove unnecessary -1 values from int file 2022-10-03 14:21:44 -07:00
virt VFIO fixes for v6.2-rc6 2023-01-23 11:56:07 -08:00
.clang-format iommufd for 6.2 2022-12-14 09:15:43 -08:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore *.rpm 2022-12-30 17:22:14 +09:00
.mailmap 25 hotfixes, mainly for MM. 13 are cc:stable. 2023-02-03 10:01:57 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: update SCTP maintainers 2023-02-02 11:35:33 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: Add myself as maintainer for arch/sh (SUPERH) 2023-02-12 13:57:09 -08:00
Makefile Linux 6.2-rc8 2023-02-12 14:10:17 -08:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.