[syzbot] [bcachefs?] possible deadlock in __bch2_trans_get

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 08b06c30a445 Merge tag 'v6.17-rc4-ksmbd-fix' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13851312580000
kernel config: https://syzkaller.appspot.com/x/.config?x=385d836f07b5a70d
dashboard link: https://syzkaller.appspot.com/bug?extid=b70ffe7893bd1110ddd0
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-08b06c30.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/516e142f1f8b/vmlinux-08b06c30.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a968d13b9737/bzImage-08b06c30.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b70ffe...@syzkaller.appspotmail.com

bcachefs (loop0): /file0/file0 offset 0: data_read_io_err
u64s 8 type extent 4099:8:U32_MAX len 8 ver 1: durability: 1 crc: c_size 8 size 8 offset 0 nonce 0 csum chacha20_poly1305_80 77fa:f532966a693125aa compress incompressible ptr: 0:34:0 gen 0
bcachefs (loop0): /file0/file0 offset 0: data read error: data_read_io_err
bcachefs (loop0): /file0/file0 offset 0: data read error, data_read_io_err
u64s 8 type extent 4099:8:U32_MAX len 8 ver 1: durability: 1 crc: c_size 8 size 8 offset 0 nonce 0 csum chacha20_poly1305_80 77fa:f532966a693125aa compress incompressible ptr: 0:34:0 gen 0
loop0 io error
============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
kworker/u4:5/1037 is trying to acquire lock:
ffff888055bec1b0 (bcachefs_btree){+.+.}-{0:0}, at: srcu_lock_acquire include/linux/srcu.h:161 [inline]
ffff888055bec1b0 (bcachefs_btree){+.+.}-{0:0}, at: srcu_read_lock include/linux/srcu.h:253 [inline]
ffff888055bec1b0 (bcachefs_btree){+.+.}-{0:0}, at: __bch2_trans_get+0x7f4/0xd80 fs/bcachefs/btree_iter.c:3505

but task is already holding lock:
ffff888051f701b0 (bcachefs_btree){+.+.}-{0:0}, at: trans_set_locked fs/bcachefs/btree_locking.h:206 [inline]
ffff888051f701b0 (bcachefs_btree){+.+.}-{0:0}, at: bch2_trans_begin+0xbe0/0x2310 fs/bcachefs/btree_iter.c:3403

other info that might help us debug this:
Possible unsafe locking scenario:

CPU0
----
lock(bcachefs_btree);
lock(bcachefs_btree);

*** DEADLOCK ***

May be due to missing lock nesting notation

5 locks held by kworker/u4:5/1037:
#0: ffff88801a479148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3211 [inline]
#0: ffff88801a479148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_scheduled_works+0x9b4/0x17b0 kernel/workqueue.c:3319
#1: ffffc900025ffbc0 ((work_completion)(&rbio->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3212 [inline]
#1: ffffc900025ffbc0 ((work_completion)(&rbio->work)){+.+.}-{0:0}, at: process_scheduled_works+0x9ef/0x17b0 kernel/workqueue.c:3319
#2: ffff888051f701b0 (bcachefs_btree){+.+.}-{0:0}, at: trans_set_locked fs/bcachefs/btree_locking.h:206 [inline]
#2: ffff888051f701b0 (bcachefs_btree){+.+.}-{0:0}, at: bch2_trans_begin+0xbe0/0x2310 fs/bcachefs/btree_iter.c:3403
#3: ffff888052f04398 (&c->btree_trans_barrier){.+.+}-{0:0}, at: srcu_lock_acquire include/linux/srcu.h:161 [inline]
#3: ffff888052f04398 (&c->btree_trans_barrier){.+.+}-{0:0}, at: srcu_read_lock include/linux/srcu.h:253 [inline]
#3: ffff888052f04398 (&c->btree_trans_barrier){.+.+}-{0:0}, at: bch2_trans_srcu_lock+0xaf/0x220 fs/bcachefs/btree_iter.c:3299
#4: ffff888052f04398 (&c->btree_trans_barrier){.+.+}-{0:0}, at: srcu_lock_acquire include/linux/srcu.h:161 [inline]
#4: ffff888052f04398 (&c->btree_trans_barrier){.+.+}-{0:0}, at: srcu_read_lock include/linux/srcu.h:253 [inline]
#4: ffff888052f04398 (&c->btree_trans_barrier){.+.+}-{0:0}, at: __bch2_trans_get+0x7f4/0xd80 fs/bcachefs/btree_iter.c:3505

stack backtrace:
CPU: 0 UID: 0 PID: 1037 Comm: kworker/u4:5 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Workqueue: events_unbound bch2_rbio_retry
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
print_deadlock_bug+0x28b/0x2a0 kernel/locking/lockdep.c:3041
check_deadlock kernel/locking/lockdep.c:3093 [inline]
validate_chain+0x1a3f/0x2140 kernel/locking/lockdep.c:3895
__lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
trans_set_locked fs/bcachefs/btree_locking.h:206 [inline]
__bch2_trans_get+0x8fd/0xd80 fs/bcachefs/btree_iter.c:3508
bch2_rbio_retry+0x1d1/0x19b0 fs/bcachefs/io_read.c:594
bch2_rbio_done fs/bcachefs/io_read.c:464 [inline]
bch2_rbio_retry+0xbf4/0x19b0 fs/bcachefs/io_read.c:667
process_one_work kernel/workqueue.c:3236 [inline]
process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3319
worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
kthread+0x70e/0x8a0 kernel/kthread.c:463
ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>


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