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Filipe Manana 65241e3ddd btrfs: release path before iget_failed() in btrfs_read_locked_inode() 
[ Upstream commit 1e1f2055ad ]

In btrfs_read_locked_inode() if we fail to lookup the inode, we jump to
the 'out' label with a path that has a read locked leaf and then we call
iget_failed(). This can result in a ABBA deadlock, since iget_failed()
triggers inode eviction and that causes the release of the delayed inode,
which must lock the delayed inode's mutex, and a task updating a delayed
inode starts by taking the node's mutex and then modifying the inode's
subvolume btree.

Syzbot reported the following lockdep splat for this:

   ======================================================
   WARNING: possible circular locking dependency detected
   syzkaller #0 Not tainted
   ------------------------------------------------------
   btrfs-cleaner/8725 is trying to acquire lock:
   ffff0000d6826a48 (&delayed_node->mutex){+.+.}-{4:4}, at: __btrfs_release_delayed_node+0xa0/0x9b0 fs/btrfs/delayed-inode.c:290

   but task is already holding lock:
   ffff0000dbeba878 (btrfs-tree-00){++++}-{4:4}, at: btrfs_tree_read_lock_nested+0x44/0x2ec fs/btrfs/locking.c:145

   which lock already depends on the new lock.

   the existing dependency chain (in reverse order) is:

   -> #1 (btrfs-tree-00){++++}-{4:4}:
          __lock_release kernel/locking/lockdep.c:5574 [inline]
          lock_release+0x198/0x39c kernel/locking/lockdep.c:5889
          up_read+0x24/0x3c kernel/locking/rwsem.c:1632
          btrfs_tree_read_unlock+0xdc/0x298 fs/btrfs/locking.c:169
          btrfs_tree_unlock_rw fs/btrfs/locking.h:218 [inline]
          btrfs_search_slot+0xa6c/0x223c fs/btrfs/ctree.c:2133
          btrfs_lookup_inode+0xd8/0x38c fs/btrfs/inode-item.c:395
          __btrfs_update_delayed_inode+0x124/0xed0 fs/btrfs/delayed-inode.c:1032
          btrfs_update_delayed_inode fs/btrfs/delayed-inode.c:1118 [inline]
          __btrfs_commit_inode_delayed_items+0x15f8/0x1748 fs/btrfs/delayed-inode.c:1141
          __btrfs_run_delayed_items+0x1ac/0x514 fs/btrfs/delayed-inode.c:1176
          btrfs_run_delayed_items_nr+0x28/0x38 fs/btrfs/delayed-inode.c:1219
          flush_space+0x26c/0xb68 fs/btrfs/space-info.c:828
          do_async_reclaim_metadata_space+0x110/0x364 fs/btrfs/space-info.c:1158
          btrfs_async_reclaim_metadata_space+0x90/0xd8 fs/btrfs/space-info.c:1226
          process_one_work+0x7e8/0x155c kernel/workqueue.c:3263
          process_scheduled_works kernel/workqueue.c:3346 [inline]
          worker_thread+0x958/0xed8 kernel/workqueue.c:3427
          kthread+0x5fc/0x75c kernel/kthread.c:463
          ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:844

   -> #0 (&delayed_node->mutex){+.+.}-{4:4}:
          check_prev_add kernel/locking/lockdep.c:3165 [inline]
          check_prevs_add kernel/locking/lockdep.c:3284 [inline]
          validate_chain kernel/locking/lockdep.c:3908 [inline]
          __lock_acquire+0x1774/0x30a4 kernel/locking/lockdep.c:5237
          lock_acquire+0x14c/0x2e0 kernel/locking/lockdep.c:5868
          __mutex_lock_common+0x1d0/0x2678 kernel/locking/mutex.c:598
          __mutex_lock kernel/locking/mutex.c:760 [inline]
          mutex_lock_nested+0x2c/0x38 kernel/locking/mutex.c:812
          __btrfs_release_delayed_node+0xa0/0x9b0 fs/btrfs/delayed-inode.c:290
          btrfs_release_delayed_node fs/btrfs/delayed-inode.c:315 [inline]
          btrfs_remove_delayed_node+0x68/0x84 fs/btrfs/delayed-inode.c:1326
          btrfs_evict_inode+0x578/0xe28 fs/btrfs/inode.c:5587
          evict+0x414/0x928 fs/inode.c:810
          iput_final fs/inode.c:1914 [inline]
          iput+0x95c/0xad4 fs/inode.c:1966
          iget_failed+0xec/0x134 fs/bad_inode.c:248
          btrfs_read_locked_inode+0xe1c/0x1234 fs/btrfs/inode.c:4101
          btrfs_iget+0x1b0/0x264 fs/btrfs/inode.c:5837
          btrfs_run_defrag_inode fs/btrfs/defrag.c:237 [inline]
          btrfs_run_defrag_inodes+0x520/0xdc4 fs/btrfs/defrag.c:309
          cleaner_kthread+0x21c/0x418 fs/btrfs/disk-io.c:1516
          kthread+0x5fc/0x75c kernel/kthread.c:463
          ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:844

   other info that might help us debug this:

    Possible unsafe locking scenario:

          CPU0                    CPU1
          ----                    ----
     rlock(btrfs-tree-00);
                                  lock(&delayed_node->mutex);
                                  lock(btrfs-tree-00);
     lock(&delayed_node->mutex);

    *** DEADLOCK ***

   1 lock held by btrfs-cleaner/8725:
    #0: ffff0000dbeba878 (btrfs-tree-00){++++}-{4:4}, at: btrfs_tree_read_lock_nested+0x44/0x2ec fs/btrfs/locking.c:145

   stack backtrace:
   CPU: 0 UID: 0 PID: 8725 Comm: btrfs-cleaner Not tainted syzkaller #0 PREEMPT
   Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/03/2025
   Call trace:
    show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C)
    __dump_stack+0x30/0x40 lib/dump_stack.c:94
    dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120
    dump_stack+0x1c/0x28 lib/dump_stack.c:129
    print_circular_bug+0x324/0x32c kernel/locking/lockdep.c:2043
    check_noncircular+0x154/0x174 kernel/locking/lockdep.c:2175
    check_prev_add kernel/locking/lockdep.c:3165 [inline]
    check_prevs_add kernel/locking/lockdep.c:3284 [inline]
    validate_chain kernel/locking/lockdep.c:3908 [inline]
    __lock_acquire+0x1774/0x30a4 kernel/locking/lockdep.c:5237
    lock_acquire+0x14c/0x2e0 kernel/locking/lockdep.c:5868
    __mutex_lock_common+0x1d0/0x2678 kernel/locking/mutex.c:598
    __mutex_lock kernel/locking/mutex.c:760 [inline]
    mutex_lock_nested+0x2c/0x38 kernel/locking/mutex.c:812
    __btrfs_release_delayed_node+0xa0/0x9b0 fs/btrfs/delayed-inode.c:290
    btrfs_release_delayed_node fs/btrfs/delayed-inode.c:315 [inline]
    btrfs_remove_delayed_node+0x68/0x84 fs/btrfs/delayed-inode.c:1326
    btrfs_evict_inode+0x578/0xe28 fs/btrfs/inode.c:5587
    evict+0x414/0x928 fs/inode.c:810
    iput_final fs/inode.c:1914 [inline]
    iput+0x95c/0xad4 fs/inode.c:1966
    iget_failed+0xec/0x134 fs/bad_inode.c:248
    btrfs_read_locked_inode+0xe1c/0x1234 fs/btrfs/inode.c:4101
    btrfs_iget+0x1b0/0x264 fs/btrfs/inode.c:5837
    btrfs_run_defrag_inode fs/btrfs/defrag.c:237 [inline]
    btrfs_run_defrag_inodes+0x520/0xdc4 fs/btrfs/defrag.c:309
    cleaner_kthread+0x21c/0x418 fs/btrfs/disk-io.c:1516
    kthread+0x5fc/0x75c kernel/kthread.c:463
    ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:844

Fix this by releasing the path before calling iget_failed().

Reported-by: syzbot+c1c6edb02bea1da754d8@syzkaller.appspotmail.com
Link: https://lore.kernel.org/linux-btrfs/694530c2.a70a0220.207337.010d.GAE@google.com/
Fixes: 69673992b1 ("btrfs: push cleanup into btrfs_read_locked_inode()")
Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2026-01-23 11:21:15 +01:00
arch x86/fpu: Clear XSTATE_BV[i] in guest XSAVE state whenever XFD[i]=1 2026-01-23 11:21:12 +01:00
block block: validate pi_offset integrity limit 2026-01-17 16:35:33 +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 cxl/port: Fix target list setup for multiple decoders sharing the same dport 2026-01-23 11:21:15 +01:00
fs btrfs: release path before iget_failed() in btrfs_read_locked_inode() 2026-01-23 11:21:15 +01:00
include ipv4: ip_tunnel: spread netdev_lockdep_set_classes() 2026-01-23 11:21:15 +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 trace: ftrace_dump_on_oops[] is not exported, make it static 2026-01-17 16:35:29 +01:00
lib lib/crypto: aes: Fix missing MMU protection for AES S-box 2026-01-17 16:35:12 +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 mm/damon/tests/core-kunit: handle alloc failures on damon_test_split_regions_of() 2026-01-08 10:17:21 +01:00
net ipv4: ip_tunnel: spread netdev_lockdep_set_classes() 2026-01-23 11:21:15 +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 kernel/kexec: change the prototype of kimage_map_segment() 2026-01-08 10:17:10 +01:00
sound ASoC: codecs: wsa883x: fix unnecessary initialisation 2026-01-23 11:21:13 +01:00
tools selftests: drv-net: Bring back tool() to driver __init__s 2026-01-17 16:35:28 +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.