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Robbie Ko 9ac63333d6 btrfs: fix deadlock in wait_current_trans() due to ignored transaction type 
commit 5037b34282 upstream.

When wait_current_trans() is called during start_transaction(), it
currently waits for a blocked transaction without considering whether
the given transaction type actually needs to wait for that particular
transaction state. The btrfs_blocked_trans_types[] array already defines
which transaction types should wait for which transaction states, but
this check was missing in wait_current_trans().

This can lead to a deadlock scenario involving two transactions and
pending ordered extents:

  1. Transaction A is in TRANS_STATE_COMMIT_DOING state

  2. A worker processing an ordered extent calls start_transaction()
     with TRANS_JOIN

  3. join_transaction() returns -EBUSY because Transaction A is in
     TRANS_STATE_COMMIT_DOING

  4. Transaction A moves to TRANS_STATE_UNBLOCKED and completes

  5. A new Transaction B is created (TRANS_STATE_RUNNING)

  6. The ordered extent from step 2 is added to Transaction B's
     pending ordered extents

  7. Transaction B immediately starts commit by another task and
     enters TRANS_STATE_COMMIT_START

  8. The worker finally reaches wait_current_trans(), sees Transaction B
     in TRANS_STATE_COMMIT_START (a blocked state), and waits
     unconditionally

  9. However, TRANS_JOIN should NOT wait for TRANS_STATE_COMMIT_START
     according to btrfs_blocked_trans_types[]

  10. Transaction B is waiting for pending ordered extents to complete

  11. Deadlock: Transaction B waits for ordered extent, ordered extent
      waits for Transaction B

This can be illustrated by the following call stacks:
  CPU0                              CPU1
                                    btrfs_finish_ordered_io()
                                      start_transaction(TRANS_JOIN)
                                        join_transaction()
                                          # -EBUSY (Transaction A is
                                          # TRANS_STATE_COMMIT_DOING)
  # Transaction A completes
  # Transaction B created
  # ordered extent added to
  # Transaction B's pending list
  btrfs_commit_transaction()
    # Transaction B enters
    # TRANS_STATE_COMMIT_START
    # waiting for pending ordered
    # extents
                                        wait_current_trans()
                                          # waits for Transaction B
                                          # (should not wait!)

Task bstore_kv_sync in btrfs_commit_transaction waiting for ordered
extents:

  __schedule+0x2e7/0x8a0
  schedule+0x64/0xe0
  btrfs_commit_transaction+0xbf7/0xda0 [btrfs]
  btrfs_sync_file+0x342/0x4d0 [btrfs]
  __x64_sys_fdatasync+0x4b/0x80
  do_syscall_64+0x33/0x40
  entry_SYSCALL_64_after_hwframe+0x44/0xa9

Task kworker in wait_current_trans waiting for transaction commit:

  Workqueue: btrfs-syno_nocow btrfs_work_helper [btrfs]
  __schedule+0x2e7/0x8a0
  schedule+0x64/0xe0
  wait_current_trans+0xb0/0x110 [btrfs]
  start_transaction+0x346/0x5b0 [btrfs]
  btrfs_finish_ordered_io.isra.0+0x49b/0x9c0 [btrfs]
  btrfs_work_helper+0xe8/0x350 [btrfs]
  process_one_work+0x1d3/0x3c0
  worker_thread+0x4d/0x3e0
  kthread+0x12d/0x150
  ret_from_fork+0x1f/0x30

Fix this by passing the transaction type to wait_current_trans() and
checking btrfs_blocked_trans_types[cur_trans->state] against the given
type before deciding to wait. This ensures that transaction types which
are allowed to join during certain blocked states will not unnecessarily
wait and cause deadlocks.

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Robbie Ko <robbieko@synology.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Cc: Motiejus Jakštys <motiejus@jakstys.lt>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2026-01-23 11:21:36 +01:00
arch iommu/sva: invalidate stale IOTLB entries for kernel address space 2026-01-23 11:21:35 +01:00
block block: zero non-PI portion of auto integrity buffer 2026-01-23 11:21:16 +01:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: seqiv - Do not use req->iv after crypto_aead_encrypt 2026-01-08 10:16:43 +01:00
Documentation dt-bindings: PCI: qcom,pcie-sm8550: Add missing required power-domains and resets 2026-01-02 12:57:27 +01:00
drivers HID: intel-ish-hid: Fix -Wcast-function-type-strict in devm_ishtp_alloc_workqueue() 2026-01-23 11:21:36 +01:00
fs btrfs: fix deadlock in wait_current_trans() due to ignored transaction type 2026-01-23 11:21:36 +01:00
include HID: intel-ish-hid: Use dedicated unbound workqueues to prevent resume blocking 2026-01-23 11:21:36 +01:00
init printk changes for 6.18 2025-10-04 11:13:11 -07:00
io_uring io_uring: move local task_work in exit cancel loop 2026-01-23 11:21:13 +01:00
ipc namespace-6.18-rc1 2025-09-29 11:20:29 -07:00
kernel hrtimer: Fix softirq base check in update_needs_ipi() 2026-01-23 11:21:28 +01:00
lib lib/buildid: use __kernel_read() for sleepable context 2026-01-23 11:21:25 +01:00
LICENSES LICENSES: Replace the obsolete address of the FSF in the GFDL-1.2 2025-07-24 11:15:39 +02:00
mm iommu/sva: invalidate stale IOTLB entries for kernel address space 2026-01-23 11:21:35 +01:00
net net: can: j1939: j1939_xtp_rx_rts_session_active(): deactivate session upon receiving the second rts 2026-01-23 11:21:24 +01:00
rust rust: bitops: fix missing _find_* functions on 32-bit ARM 2026-01-23 11:21:12 +01:00
samples samples/ftrace: Adjust LoongArch register restore order in direct calls 2026-01-08 10:17:11 +01:00
scripts mcb: Add missing modpost build support 2026-01-08 10:16:47 +01:00
security landlock: Fix wrong type usage 2026-01-23 11:21:22 +01:00
sound ASoC: codecs: wsa881x: fix unnecessary initialisation 2026-01-23 11:21:28 +01:00
tools tools/testing/selftests: fix gup_longterm for unknown fs 2026-01-23 11:21:25 +01:00
usr gen_init_cpio: Ignore fsync() returning EINVAL on pipes 2025-10-07 09:53:05 -07:00
virt KVM: Fix last_boosted_vcpu index assignment bug 2026-01-02 12:57:21 +01:00
.clang-format memblock: drop for_each_free_mem_pfn_range_in_zone_from() 2025-09-14 08:49:03 +03:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: remove Alyssa Rosenzweig 2025-09-18 21:17:31 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore .gitignore: ignore compile_commands.json globally 2025-08-12 15:53:55 -07:00
.mailmap 8 hotfixes. 4 are cc:stable, 7 are against mm/. 2025-11-26 12:38:05 -08:00
.pylintrc tools: docs: parse-headers.py: move it from sphinx dir 2025-08-29 15:54:42 -06:00
.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: mark ISDN subsystem as orphan 2025-10-27 17:49:45 -07:00
Kbuild sched: Make migrate_{en,dis}able() inline 2025-09-25 09:57:16 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS soc: fixes for 6.18, part 4 2025-11-28 09:57:31 -08:00
Makefile Linux 6.18.6 2026-01-17 16:35:34 +01:00
README README: Fix spelling 2024-03-18 03:36:32 -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 reStructuredText 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.