[syzbot] [jfs?] [xfs?] [bcachefs?] INFO: task hung in sb_start_write (2)

[syzbot] [jfs?] [xfs?] [bcachefs?] INFO: task hung in sb_start_write (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    a5806cd506af Linux 6.15-rc7
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11923f68580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=3340af1a8845dd35
dashboard link: https://syzkaller.appspot.com/bug?extid=b3fba2e269970207b61d
compiler:       Debian clang version 20.1.2 (++20250402124445+58df0ef89dd6-1~exp1~20250402004600.97), Debian LLD 20.1.2

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/652000eacd92/disk-a5806cd5.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/2b445a74e31e/vmlinux-a5806cd5.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0a4ef01f165f/bzImage-a5806cd5.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b3fba2e269970207b61d@syzkaller.appspotmail.com

INFO: task syz.9.533:10335 blocked for more than 143 seconds.
      Not tainted 6.15.0-rc7-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.9.533       state:D stack:24344 pid:10335 tgid:10334 ppid:7718   task_flags:0x400140 flags:0x00000004
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5382 [inline]
 __schedule+0x168f/0x4c70 kernel/sched/core.c:6767
 __schedule_loop kernel/sched/core.c:6845 [inline]
 schedule+0x165/0x360 kernel/sched/core.c:6860
 percpu_rwsem_wait+0x2ab/0x300 kernel/locking/percpu-rwsem.c:162
 __percpu_down_read+0xe3/0x120 kernel/locking/percpu-rwsem.c:177
 percpu_down_read include/linux/percpu-rwsem.h:66 [inline]
 __sb_start_write include/linux/fs.h:1783 [inline]
 sb_start_write+0x185/0x1c0 include/linux/fs.h:1919
 mnt_want_write+0x41/0x90 fs/namespace.c:556
 open_last_lookups fs/namei.c:3789 [inline]
 path_openat+0x85d/0x3830 fs/namei.c:4036
 do_filp_open+0x1fa/0x410 fs/namei.c:4066
 do_sys_openat2+0x121/0x1c0 fs/open.c:1429
 do_sys_open fs/open.c:1444 [inline]
 __do_sys_openat fs/open.c:1460 [inline]
 __se_sys_openat fs/open.c:1455 [inline]
 __x64_sys_openat+0x138/0x170 fs/open.c:1455
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f8e2a18e969
RSP: 002b:00007f8e2b0be038 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007f8e2a3b5fa0 RCX: 00007f8e2a18e969
RDX: 000000000000275a RSI: 0000200000000100 RDI: ffffffffffffff9c
RBP: 00007f8e2a210ab1 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f8e2a3b5fa0 R15: 00007fffe529a348
 </TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/31:
 #0: ffffffff8df3dee0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #0: ffffffff8df3dee0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline]
 #0: ffffffff8df3dee0 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180 kernel/locking/lockdep.c:6764
5 locks held by kworker/u8:2/36:
2 locks held by kworker/u8:6/1089:
2 locks held by getty/5583:
 #0: ffff88803055e0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
 #1: ffffc90002ffe2f0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x43e/0x1400 drivers/tty/n_tty.c:2222
1 lock held by udevd/9862:
2 locks held by udevd/10189:
 #0: ffff888022a2e3a0 (&sb->s_type->i_mutex_key#7){++++}-{4:4}, at: inode_lock_shared include/linux/fs.h:877 [inline]
 #0: ffff888022a2e3a0 (&sb->s_type->i_mutex_key#7){++++}-{4:4}, at: blkdev_read_iter+0x2f8/0x440 block/fops.c:808
 #1: ffff8880b88399d8 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x2a/0x140 kernel/sched/core.c:605
1 lock held by syz.9.533/10335:
 #0: ffff88802f0e0420 (sb_writers#25){++++}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:556
3 locks held by syz-executor/12892:
 #0: ffff8880b89399d8 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x2a/0x140 kernel/sched/core.c:605
 #1: ffff8880b8923b08 (&per_cpu_ptr(group->pcpu, cpu)->seq){-.-.}-{0:0}, at: psi_task_switch+0x39e/0x6d0 kernel/sched/psi.c:987
 #2: ffff88807a093758 (&sb->s_type->i_lock_key#9){+.+.}-{3:3}, at: spin_trylock include/linux/spinlock.h:361 [inline]
 #2: ffff88807a093758 (&sb->s_type->i_lock_key#9){+.+.}-{3:3}, at: lock_for_kill+0x84/0x210 fs/dcache.c:705
2 locks held by syz.2.1023/13285:
2 locks held by dhcpcd-run-hook/13307:
 #0: ffff8880b89399d8 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x2a/0x140 kernel/sched/core.c:605
 #1: ffff8880b8923b08 (&per_cpu_ptr(group->pcpu, cpu)->seq){-.-.}-{0:0}, at: psi_task_switch+0x39e/0x6d0 kernel/sched/psi.c:987

=============================================

NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 31 Comm: khungtaskd Not tainted 6.15.0-rc7-syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
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:158 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:274 [inline]
 watchdog+0xfee/0x1030 kernel/hung_task.c:437
 kthread+0x711/0x8a0 kernel/kthread.c:464
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:153
 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: 13310 Comm: rm Not tainted 6.15.0-rc7-syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
RIP: 0010:file_ref_inc include/linux/file_ref.h:121 [inline]
RIP: 0010:get_file include/linux/fs.h:1133 [inline]
RIP: 0010:__mmap_new_file_vma mm/vma.c:2352 [inline]
RIP: 0010:__mmap_new_vma mm/vma.c:2417 [inline]
RIP: 0010:__mmap_region mm/vma.c:2519 [inline]
RIP: 0010:mmap_region+0xf23/0x1e50 mm/vma.c:2597
Code: 24 18 01 00 00 48 89 44 24 50 49 8d be 60 01 00 00 be 08 00 00 00 e8 1c 3f 0e 00 41 bf 01 00 00 00 f0 4d 0f c1 be 60 01 00 00 <31> ff 4c 89 fe e8 83 6c ae ff 4d 85 ff 78 74 e8 99 67 ae ff 4c 8b
RSP: 0018:ffffc9000418f2c0 EFLAGS: 00000202
RAX: ffffc9000418f301 RBX: ffff88806733f2a0 RCX: ffffffff82118924
RDX: 0000000000000001 RSI: 0000000000000008 RDI: ffff88807e407820
RBP: ffffc9000418f730 R08: ffff88807e407827 R09: 1ffff1100fc80f04
R10: dffffc0000000000 R11: ffffed100fc80f05 R12: ffff88806733f280
R13: ffffc9000418f3d0 R14: ffff88807e4076c0 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8881261f6000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055aa8d186008 CR3: 000000007f374000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 do_mmap+0xc68/0x1100 mm/mmap.c:561
 vm_mmap_pgoff+0x31b/0x4c0 mm/util.c:579
 elf_map fs/binfmt_elf.c:387 [inline]
 elf_load+0x140/0x6c0 fs/binfmt_elf.c:414
 load_elf_interp+0x469/0xaf0 fs/binfmt_elf.c:681
 load_elf_binary+0x19d2/0x27a0 fs/binfmt_elf.c:1246
 search_binary_handler fs/exec.c:1778 [inline]
 exec_binprm fs/exec.c:1810 [inline]
 bprm_execve+0x999/0x1440 fs/exec.c:1862
 do_execveat_common+0x510/0x6a0 fs/exec.c:1968
 do_execve fs/exec.c:2042 [inline]
 __do_sys_execve fs/exec.c:2118 [inline]
 __se_sys_execve fs/exec.c:2113 [inline]
 __x64_sys_execve+0x94/0xb0 fs/exec.c:2113
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6e5ef70107
Code: Unable to access opcode bytes at 0x7f6e5ef700dd.
RSP: 002b:00007fff92965db8 EFLAGS: 00000246 ORIG_RAX: 000000000000003b
RAX: ffffffffffffffda RBX: 00005577b8e42fe0 RCX: 00007f6e5ef70107
RDX: 00005577b8e43000 RSI: 00005577b8e42fe0 RDI: 00005577b8e43088
RBP: 00005577b8e43088 R08: 00007fff92968e28 R09: 0000000000000000
R10: 0000000000000008 R11: 0000000000000246 R12: 00005577b8e43000
R13: 00007f6e5f135e8b R14: 00005577b8e43000 R15: 0000000000000000
 </TASK>


---
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If the report is already addressed, let syzbot know by replying with:
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If you want to undo deduplication, reply with:
#syz undup

Re: [syzbot] [kernfs?] [ext4?] INFO: task hung in sb_start_write (2)

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    f9a2394a2348 Merge tag 'mm-hotfixes-stable-2026-08-06-18-4..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1379cfb9580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=98da55a882774dfe
dashboard link: https://syzkaller.appspot.com/bug?extid=b3fba2e269970207b61d
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14b9d7b9580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b3fba2e269970207b61d@syzkaller.appspotmail.com

INFO: task syz-executor328:5959 blocked for more than 15 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor328 state:D stack:28328 pid:5959  tgid:5959  ppid:5947   task_flags:0x400040 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5510 [inline]
 __schedule+0x16dc/0x5500 kernel/sched/core.c:7234
 __schedule_loop kernel/sched/core.c:7311 [inline]
 schedule+0x164/0x2b0 kernel/sched/core.c:7326
 percpu_rwsem_wait+0x32d/0x4a0 kernel/locking/percpu-rwsem.c:164
 __percpu_down_read+0xf8/0x140 kernel/locking/percpu-rwsem.c:180
 percpu_down_read_internal include/linux/percpu-rwsem.h:67 [inline]
 percpu_down_read_freezable include/linux/percpu-rwsem.h:83 [inline]
 __sb_start_write include/linux/fs/super.h:19 [inline]
 sb_start_write+0x18e/0x1c0 include/linux/fs/super.h:125
 mnt_want_write+0x41/0x90 fs/namespace.c:494
 do_tmpfile+0x6c/0x240 fs/namei.c:4817
 path_openat+0x3095/0x3850 fs/namei.c:4854
 do_file_open+0x23e/0x4a0 fs/namei.c:4892
 do_sys_openat2+0x115/0x200 fs/open.c:1368
 do_sys_open fs/open.c:1374 [inline]
 __do_sys_openat fs/open.c:1390 [inline]
 __se_sys_openat fs/open.c:1385 [inline]
 __x64_sys_openat+0x138/0x170 fs/open.c:1385
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f3fb490aaf7
RSP: 002b:00007fff7f2f6f10 EFLAGS: 00000202 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 0000555578a51400 RCX: 00007f3fb490aaf7
RDX: 0000000000410001 RSI: 00007f3fb494a764 RDI: ffffffffffffff9c
RBP: 00007f3fb494a764 R08: 0000000000000000 R09: 0000000000000000
R10: 00000000000001b6 R11: 0000000000000202 R12: 00007fff7f2f70d8
R13: 0000000000000002 R14: 00007f3fb4970c80 R15: 0000000000000002
 </TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/38:
 #0: ffffffff8e1c3000 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
 #0: ffffffff8e1c3000 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:840 [inline]
 #0: ffffffff8e1c3000 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180 kernel/locking/lockdep.c:6775
2 locks held by getty/5356:
 #0: ffff88803688d0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
 #1: ffffc90003cc62e0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x460/0x1360 drivers/tty/n_tty.c:2211
1 lock held by syz-executor328/5959:
 #0: ffff888035a88500 (sb_writers#4){++++}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:494

=============================================

NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 38 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 nmi_cpu_backtrace+0x274/0x2d0 lib/nmi_backtrace.c:122
 nmi_trigger_cpumask_backtrace+0x17a/0x380 lib/nmi_backtrace.c:65
 trigger_all_cpu_backtrace include/linux/nmi.h:162 [inline]
 __sys_info lib/sys_info.c:157 [inline]
 sys_info+0x135/0x170 lib/sys_info.c:165
 check_hung_uninterruptible_tasks kernel/hung_task.c:353 [inline]
 watchdog+0xfd7/0x1030 kernel/hung_task.c:561
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:64
Code: cb 6e 02 e9 13 cf 03 00 cc cc cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 66 90 0f 00 2d 33 44 24 00 fb f4 <c3> cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc 90 90 90 90 90
RSP: 0018:ffffffff8de07de0 EFLAGS: 00000242
RAX: 000000000009a1e9 RBX: ffffffff81998590 RCX: 0000000080000001
RDX: 0000000000000001 RSI: ffffffff8d887e30 RDI: ffffffff8bca6d80
RBP: ffffffff8de07eb8 R08: ffff8880b8633d5b R09: 1ffff110170c67ab
R10: dffffc0000000000 R11: ffffed10170c67ac R12: 0000000000000000
R13: 1ffffffff1bdede8 R14: 1ffffffff1bc0fc4 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff888125c36000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000563216b981d0 CR3: 000000000dfb0000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 arch_safe_halt arch/x86/kernel/process.c:767 [inline]
 default_idle+0x9/0x20 arch/x86/kernel/process.c:768
 default_idle_call+0x72/0xb0 kernel/sched/idle.c:122
 cpuidle_idle_call kernel/sched/idle.c:199 [inline]
 do_idle+0x2e0/0x540 kernel/sched/idle.c:355
 cpu_startup_entry+0x43/0x60 kernel/sched/idle.c:454
 rest_init+0x2de/0x300 init/main.c:717
 start_kernel+0x392/0x3e0 init/main.c:1175
 x86_64_start_reservations+0x24/0x30 arch/x86/kernel/head64.c:310
 x86_64_start_kernel+0x137/0x1b0 arch/x86/kernel/head64.c:291
 common_startup_64+0x13e/0x157
 </TASK>


---
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