[syzbot] [bcachefs?] INFO: task hung in bch2_direct_write (2)

[syzbot <syzbot+d5daa7d9e8e8d49ec379@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    ee94b00c1a64 Merge tag 'block-6.17-20250815' of git://git...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1586bdbc580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=98e114f4eb77e551
dashboard link: https://syzkaller.appspot.com/bug?extid=d5daa7d9e8e8d49ec379
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12bc53a2580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16bc53a2580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d3a276780499/disk-ee94b00c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9d0179cf0059/vmlinux-ee94b00c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/93f6f92d9369/bzImage-ee94b00c.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/51d8a3d7de8c/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d5daa7d9e8e8d49ec379@syzkaller.appspotmail.com

INFO: task syz.3.29:6250 blocked for more than 143 seconds.
      Tainted: G        W           6.17.0-rc1-syzkaller-00165-gee94b00c1a64 #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.3.29        state:D stack:15112 pid:6250  tgid:6249  ppid:5983   task_flags:0x400140 flags:0x00004006
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5357 [inline]
 __schedule+0x16f3/0x4c20 kernel/sched/core.c:6961
 __schedule_loop kernel/sched/core.c:7043 [inline]
 rt_mutex_schedule+0x77/0xf0 kernel/sched/core.c:7339
 rt_mutex_slowlock_block kernel/locking/rtmutex.c:1647 [inline]
 __rt_mutex_slowlock kernel/locking/rtmutex.c:1721 [inline]
 __rt_mutex_slowlock_locked+0x1e04/0x25e0 kernel/locking/rtmutex.c:1760
 rt_mutex_slowlock+0xb5/0x160 kernel/locking/rtmutex.c:1800
 __rt_mutex_lock kernel/locking/rtmutex.c:1815 [inline]
 rwbase_write_lock+0x14f/0x750 kernel/locking/rwbase_rt.c:244
 inode_lock include/linux/fs.h:869 [inline]
 bch2_direct_write+0x19b/0x2cf0 fs/bcachefs/fs-io-direct.c:613
 bch2_write_iter+0x192/0x2ba0 fs/bcachefs/fs-io-buffered.c:1064
 iter_file_splice_write+0x9cb/0x10b0 fs/splice.c:738
 do_splice_from fs/splice.c:935 [inline]
 direct_splice_actor+0x104/0x160 fs/splice.c:1158
 splice_direct_to_actor+0x5b3/0xcd0 fs/splice.c:1102
 do_splice_direct_actor fs/splice.c:1201 [inline]
 do_splice_direct+0x187/0x270 fs/splice.c:1227
 do_sendfile+0x4ec/0x7f0 fs/read_write.c:1370
 __do_sys_sendfile64 fs/read_write.c:1431 [inline]
 __se_sys_sendfile64+0x13e/0x190 fs/read_write.c:1417
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fbe7bc8ebe9
RSP: 002b:00007fbe7b2f6038 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007fbe7beb5fa0 RCX: 00007fbe7bc8ebe9
RDX: 0000000000000000 RSI: 0000000000000005 RDI: 0000000000000004
RBP: 00007fbe7bd11e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000020fffe82 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fbe7beb6038 R14: 00007fbe7beb5fa0 R15: 00007ffe44413258
 </TASK>
INFO: lockdep is turned off.
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 38 Comm: khungtaskd Tainted: G        W           6.17.0-rc1-syzkaller-00165-gee94b00c1a64 #0 PREEMPT_{RT,(full)} 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 nmi_cpu_backtrace+0x39e/0x3d0 lib/nmi_backtrace.c:113
 nmi_trigger_cpumask_backtrace+0x17a/0x300 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:160 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:328 [inline]
 watchdog+0xf93/0xfe0 kernel/hung_task.c:491
 kthread+0x711/0x8a0 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>
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 6508 Comm: syz-executor Tainted: G        W           6.17.0-rc1-syzkaller-00165-gee94b00c1a64 #0 PREEMPT_{RT,(full)} 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
RIP: 0010:__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
RIP: 0010:_raw_spin_lock_irqsave+0x96/0xf0 kernel/locking/spinlock.c:162
Code: 24 20 4c 8b 74 24 20 fa 41 f7 c6 00 02 00 00 74 05 e8 fe 83 cc f6 bf 01 00 00 00 e8 94 3c 96 f6 48 8d 7b 18 31 f6 31 d2 31 c9 <41> b8 01 00 00 00 45 31 c9 ff 75 08 e8 29 6f a2 f6 48 83 c4 08 48
RSP: 0018:ffffc900053179a0 EFLAGS: 00000046
RAX: 1ffff11004e13dc6 RBX: ffff8880b8941fc0 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8880b8941fd8
RBP: ffffc90005317a30 R08: ffffffff8f1d3a37 R09: 1ffffffff1e3a746
R10: dffffc0000000000 R11: fffffbfff1e3a747 R12: dffffc0000000000
R13: ffff8880b8941fc0 R14: 0000000000000a02 R15: 1ffff92000a62f34
FS:  000055555c1f4500(0000) GS:ffff8881269c5000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f320dbc7000 CR3: 00000000283f2000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 rt_mutex_slowunlock+0xb0/0x8a0 kernel/locking/rtmutex.c:1417
 spin_unlock include/linux/spinlock_rt.h:105 [inline]
 __free_frozen_pages+0x736/0xce0 mm/page_alloc.c:2924
 vfree+0x2ad/0x470 mm/vmalloc.c:3434
 bch2_fs_btree_write_buffer_exit+0x1ac/0x1e0 fs/bcachefs/btree_write_buffer.c:871
 __bch2_fs_free fs/bcachefs/super.c:615 [inline]
 bch2_fs_release+0x297/0x830 fs/bcachefs/super.c:667
 kobject_cleanup lib/kobject.c:689 [inline]
 kobject_release lib/kobject.c:720 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x22b/0x480 lib/kobject.c:737
 deactivate_locked_super+0xbc/0x130 fs/super.c:474
 cleanup_mnt+0x425/0x4c0 fs/namespace.c:1378
 task_work_run+0x1d1/0x260 kernel/task_work.c:227
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 exit_to_user_mode_loop+0xec/0x110 kernel/entry/common.c:43
 exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
 do_syscall_64+0x2bd/0x3b0 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fcfa6f4ff17
Code: a8 ff ff ff f7 d8 64 89 01 48 83 c8 ff c3 0f 1f 44 00 00 31 f6 e9 09 00 00 00 66 0f 1f 84 00 00 00 00 00 b8 a6 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 01 c3 48 c7 c2 a8 ff ff ff f7 d8 64 89 02 b8
RSP: 002b:00007ffd6f17d858 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 00007fcfa6fd1c05 RCX: 00007fcfa6f4ff17
RDX: 0000000000000000 RSI: 0000000000000009 RDI: 00007ffd6f17d910
RBP: 00007ffd6f17d910 R08: 0000000000000000 R09: 0000000000000000
R10: 00000000ffffffff R11: 0000000000000246 R12: 00007ffd6f17e9a0
R13: 00007fcfa6fd1c05 R14: 000000000005f3e5 R15: 00007ffd6f17e9e0
 </TASK>


---
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