syzbot
INFO: task hung in do_get_write_access
Status:
upstream: reported C repro on 2026/08/05 00:11
Reported-by: syzbot+9e3d85789d3996cc829c@syzkaller.appspotmail.com
First crash: 4d21h, last: 1d04h
Sample crash report:
INFO: task syz.0.207:4616 blocked for more than 143 seconds.
Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.207 state:D stack:27632 pid:4616 ppid:4381 flags:0x00004004
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5246 [inline]
__schedule+0x107f/0x4030 kernel/sched/core.c:6563
schedule+0xb9/0x180 kernel/sched/core.c:6639
io_schedule+0x7c/0xd0 kernel/sched/core.c:8799
bit_wait_io+0xd/0xc0 kernel/sched/wait_bit.c:209
__wait_on_bit+0x9b/0x2c0 kernel/sched/wait_bit.c:49
out_of_line_wait_on_bit+0x138/0x190 kernel/sched/wait_bit.c:64
wait_on_bit_io include/linux/wait_bit.h:101 [inline]
do_get_write_access+0x605/0xf20 fs/jbd2/transaction.c:1115
jbd2_journal_get_write_access+0x108/0x140 fs/jbd2/transaction.c:1250
__ext4_journal_get_write_access+0x24b/0x6e0 fs/ext4/ext4_jbd2.c:235
ext4_reserve_inode_write+0x201/0x290 fs/ext4/inode.c:5945
__ext4_mark_inode_dirty+0x161/0x760 fs/ext4/inode.c:6119
ext4_dirty_inode+0xbf/0x100 fs/ext4/inode.c:6156
__mark_inode_dirty+0x2e7/0xe80 fs/fs-writeback.c:2500
generic_update_time fs/inode.c:1946 [inline]
inode_update_time fs/inode.c:1959 [inline]
__file_update_time+0x21d/0x240 fs/inode.c:2147
file_update_time+0x2f3/0x370 fs/inode.c:2178
ext4_page_mkwrite+0x1a9/0x10d0 fs/ext4/inode.c:6274
do_page_mkwrite+0x16b/0x5c0 mm/memory.c:3009
do_shared_fault mm/memory.c:4694 [inline]
do_fault mm/memory.c:4762 [inline]
handle_pte_fault mm/memory.c:5029 [inline]
__handle_mm_fault mm/memory.c:5171 [inline]
handle_mm_fault+0x199c/0x3d40 mm/memory.c:5292
do_user_addr_fault+0x58e/0xb20 arch/x86/mm/fault.c:1338
handle_page_fault arch/x86/mm/fault.c:1429 [inline]
exc_page_fault+0x60/0x100 arch/x86/mm/fault.c:1482
asm_exc_page_fault+0x22/0x30 arch/x86/include/asm/idtentry.h:608
RIP: 0033:0x7f1bf186ba23
RSP: 002b:00007ffe23d52380 EFLAGS: 00010246
RAX: 000000000003fde8 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000001b2e824000 RSI: 0000000000040000 RDI: 00007f1bf1be0708
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 00007ffe23d52610
</TASK>
Showing all locks held in the system:
1 lock held by rcu_tasks_kthre/12:
#0: ffffffff8cb2e4f0 (rcu_tasks.tasks_gp_mutex){+.+.}-{3:3}, at: rcu_tasks_one_gp+0x33/0xef0 kernel/rcu/tasks.h:517
1 lock held by rcu_tasks_trace/13:
#0: ffffffff8cb2ed10 (rcu_tasks_trace.tasks_gp_mutex){+.+.}-{3:3}, at: rcu_tasks_one_gp+0x33/0xef0 kernel/rcu/tasks.h:517
1 lock held by khungtaskd/28:
#0: ffffffff8cb2db60 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:350 [inline]
#0: ffffffff8cb2db60 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:791 [inline]
#0: ffffffff8cb2db60 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x51/0x290 kernel/locking/lockdep.c:6527
6 locks held by kworker/u4:3/47:
#0: ffff88801ae80938 ((wq_completion)writeback){+.+.}-{0:0}, at: process_one_work+0x7b4/0x1160 kernel/workqueue.c:2267
#1: ffffc90000b87d00 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: process_one_work+0x7b4/0x1160 kernel/workqueue.c:2267
#2: ffff88807f6620e0 (&type->s_umount_key#32){++++}-{3:3}, at: trylock_super+0x1c/0xf0 fs/super.c:415
#3: ffff88807f664c18 (&sbi->s_writepages_rwsem){.+.+}-{0:0}, at: ext4_writepages+0x213/0x2e70 fs/ext4/inode.c:2717
#4: ffff88807f666990 (jbd2_handle){++++}-{0:0}, at: start_this_handle+0x2014/0x2240 fs/jbd2/transaction.c:463
#5: ffff888074340c90 (&ei->i_data_sem){++++}-{3:3}, at: ext4_map_blocks+0x914/0x1a90 fs/ext4/inode.c:674
2 locks held by getty/4029:
#0: ffff88814d732098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x21/0x70 drivers/tty/tty_ldisc.c:244
#1: ffffc9000327b2f0 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x41e/0x1360 drivers/tty/n_tty.c:2198
3 locks held by syz.0.207/4616:
#0: ffff88807a1144d8 (&mm->mmap_lock){++++}-{3:3}, at: mmap_read_trylock include/linux/mmap_lock.h:136 [inline]
#0: ffff88807a1144d8 (&mm->mmap_lock){++++}-{3:3}, at: get_mmap_lock_carefully mm/memory.c:5320 [inline]
#0: ffff88807a1144d8 (&mm->mmap_lock){++++}-{3:3}, at: lock_mm_and_find_vma+0x2e/0x2f0 mm/memory.c:5382
#1: ffff88807f662558 (sb_pagefaults){.+.+}-{0:0}, at: __sb_start_write include/linux/fs.h:1891 [inline]
#1: ffff88807f662558 (sb_pagefaults){.+.+}-{0:0}, at: sb_start_pagefault include/linux/fs.h:1995 [inline]
#1: ffff88807f662558 (sb_pagefaults){.+.+}-{0:0}, at: ext4_page_mkwrite+0x192/0x10d0 fs/ext4/inode.c:6273
#2: ffff88807f666990 (jbd2_handle){++++}-{0:0}, at: start_this_handle+0x2014/0x2240 fs/jbd2/transaction.c:463
=============================================
NMI backtrace for cpu 0
CPU: 0 PID: 28 Comm: khungtaskd Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
<TASK>
dump_stack_lvl+0x188/0x24e lib/dump_stack.c:106
nmi_cpu_backtrace+0x3e6/0x460 lib/nmi_backtrace.c:111
nmi_trigger_cpumask_backtrace+0x1d4/0x450 lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:148 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:220 [inline]
watchdog+0xf0e/0xf50 kernel/hung_task.c:377
kthread+0x29d/0x330 kernel/kthread.c:376
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
</TASK>
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 3620 Comm: syslogd Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:orc_find arch/x86/kernel/unwind_orc.c:171 [inline]
RIP: 0010:unwind_next_frame+0x1ef/0x1fd0 arch/x86/kernel/unwind_orc.c:448
Code: 00 00 45 8b 45 00 41 ff c0 4b 8d 04 64 48 8d 94 00 64 f5 9a 8e 4b 8d 04 40 48 8d 84 00 64 f5 9a 8e 48 3d 9c de 3f 8f 0f 97 c0 <48> 81 fa 9c de 3f 8f 0f 83 67 16 00 00 84 c0 0f 85 69 16 00 00 45
RSP: 0018:ffffc90003277540 EFLAGS: 00000283
RAX: ffffffff8f18a100 RBX: ffffc900032775e8 RCX: ffffffff96c17100
RDX: ffffffff8f18a1b2 RSI: 000000000009607a RDI: ffffffff8138fb37
RBP: dffffc0000000000 R08: 000000000014f214 R09: 0000000000000006
R10: dffffc0000000000 R11: fffff5200064eec9 R12: 000000000014f20d
R13: ffffffff8f5c9018 R14: ffffffff882c5e19 R15: 0000000000072c5e
FS: 00007f0bbffbac80(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055c13c50c168 CR3: 000000007f509000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
arch_stack_walk+0x10c/0x140 arch/x86/kernel/stacktrace.c:25
stack_trace_save+0xa6/0xf0 kernel/stacktrace.c:122
kasan_save_stack mm/kasan/common.c:46 [inline]
kasan_set_track+0x4b/0x70 mm/kasan/common.c:53
kasan_save_free_info+0x27/0x40 mm/kasan/generic.c:516
____kasan_slab_free+0x126/0x1f0 mm/kasan/common.c:237
kasan_slab_free include/linux/kasan.h:177 [inline]
slab_free_hook mm/slub.c:1729 [inline]
slab_free_freelist_hook+0x133/0x1b0 mm/slub.c:1755
slab_free mm/slub.c:3687 [inline]
kmem_cache_free+0xf7/0x2a0 mm/slub.c:3709
__unix_dgram_recvmsg+0x9f9/0xd90 net/unix/af_unix.c:2531
sock_recvmsg_nosec net/socket.c:1023 [inline]
sock_recvmsg net/socket.c:1041 [inline]
sock_read_iter+0x2da/0x3a0 net/socket.c:1122
call_read_iter include/linux/fs.h:2259 [inline]
new_sync_read fs/read_write.c:389 [inline]
vfs_read+0x471/0x960 fs/read_write.c:470
ksys_read+0x14d/0x260 fs/read_write.c:613
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f0bc010a407
Code: 48 89 fa 4c 89 df e8 38 aa 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff
RSP: 002b:00007ffd06ebca40 EFLAGS: 00000202 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007f0bbffbac80 RCX: 00007f0bc010a407
RDX: 00000000000000ff RSI: 0000563e333b3950 RDI: 0000000000000000
RBP: 0000563e333b3910 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 0000563e333b399e
R13: 0000000000000000 R14: 0000563e333b3950 R15: 0000563e0fe8cd98
</TASK>
Struck through repros no longer work on HEAD.