Re: [syzbot] [netfs?] kernel BUG in netfs_perform_write

[syzbot <syzbot+b73c7d94a151e2ee1e9b@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
INFO: task hung in v9fs_evict_inode

INFO: task syz-executor:10275 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor    state:D stack:23976 pid:10275 tgid:10275 ppid:1      task_flags:0x400140 flags:0x00004004
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5357 [inline]
 __schedule+0x1190/0x5de0 kernel/sched/core.c:6961
 __schedule_loop kernel/sched/core.c:7043 [inline]
 schedule+0xe7/0x3a0 kernel/sched/core.c:7058
 netfs_wait_for_outstanding_io include/linux/netfs.h:552 [inline]
 v9fs_evict_inode+0x26f/0x300 fs/9p/vfs_inode.c:348
 evict+0x3e3/0x920 fs/inode.c:810
 iput_final fs/inode.c:1897 [inline]
 iput fs/inode.c:1923 [inline]
 iput+0x521/0x880 fs/inode.c:1909
 dentry_unlink_inode+0x29c/0x480 fs/dcache.c:466
 __dentry_kill+0x1d0/0x600 fs/dcache.c:669
 dput.part.0+0x4b1/0x9b0 fs/dcache.c:911
 dput fs/dcache.c:901 [inline]
 do_one_tree fs/dcache.c:1607 [inline]
 shrink_dcache_for_umount+0x159/0x3e0 fs/dcache.c:1621
 generic_shutdown_super+0x6c/0x390 fs/super.c:621
 kill_anon_super+0x3a/0x60 fs/super.c:1282
 v9fs_kill_super+0x3d/0xa0 fs/9p/vfs_super.c:195
 deactivate_locked_super+0xc1/0x1a0 fs/super.c:474
 deactivate_super fs/super.c:507 [inline]
 deactivate_super+0xde/0x100 fs/super.c:503
 cleanup_mnt+0x225/0x450 fs/namespace.c:1375
 task_work_run+0x150/0x240 kernel/task_work.c:227
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 exit_to_user_mode_loop+0xeb/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+0x3f6/0x4c0 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fcecc38ff17
RSP: 002b:00007ffd3a66f178 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 00007fcecc411c05 RCX: 00007fcecc38ff17
RDX: 0000000000000000 RSI: 0000000000000009 RDI: 00007ffd3a66f230
RBP: 00007ffd3a66f230 R08: 0000000000000000 R09: 0000000000000000
R10: 00000000ffffffff R11: 0000000000000246 R12: 00007ffd3a6702c0
R13: 00007fcecc411c05 R14: 000000000003f589 R15: 00007ffd3a670300
 </TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/31:
 #0: ffffffff8e5c1260 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #0: ffffffff8e5c1260 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline]
 #0: ffffffff8e5c1260 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x36/0x1c0 kernel/locking/lockdep.c:6775
2 locks held by kworker/u8:3/37:
 #0: ffff88801b881148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work+0x12a2/0x1b70 kernel/workqueue.c:3211
 #1: ffffc90000ad7d10 ((work_completion)(&rreq->cleanup_work)){+.+.}-{0:0}, at: process_one_work+0x929/0x1b70 kernel/workqueue.c:3212
2 locks held by getty/5606:
 #0: ffff88814d69e0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x24/0x80 drivers/tty/tty_ldisc.c:243
 #1: ffffc900036bb2f0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x41b/0x14f0 drivers/tty/n_tty.c:2222
1 lock held by syz-executor/10275:
 #0: ffff88805bc120e0 (&type->s_umount_key#68){+.+.}-{4:4}, at: __super_lock fs/super.c:57 [inline]
 #0: ffff88805bc120e0 (&type->s_umount_key#68){+.+.}-{4:4}, at: __super_lock_excl fs/super.c:72 [inline]
 #0: ffff88805bc120e0 (&type->s_umount_key#68){+.+.}-{4:4}, at: deactivate_super fs/super.c:506 [inline]
 #0: ffff88805bc120e0 (&type->s_umount_key#68){+.+.}-{4:4}, at: deactivate_super+0xd6/0x100 fs/super.c:503
1 lock held by syz-executor/14777:
 #0: ffffffff8e5cc6c0 (rcu_state.barrier_mutex){+.+.}-{4:4}, at: rcu_barrier+0x48/0x6e0 kernel/rcu/tree.c:3815

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

NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 31 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 nmi_cpu_backtrace+0x27b/0x390 lib/nmi_backtrace.c:113
 nmi_trigger_cpumask_backtrace+0x29c/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+0xf0e/0x1260 kernel/hung_task.c:491
 kthread+0x3c2/0x780 kernel/kthread.c:463
 ret_from_fork+0x5d4/0x6f0 arch/x86/kernel/process.c:148
 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: 12 Comm: kworker/u8:0 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Workqueue: events_unbound toggle_allocation_gate
RIP: 0010:__bfs+0x1ba/0x290 kernel/locking/lockdep.c:1815
Code: 01 15 44 29 cb 81 e3 ff 0f 00 00 39 1d df f5 45 14 48 89 04 f5 00 6a 98 96 73 0c 89 1d cf f5 45 14 eb 04 4c 89 78 30 48 8b 00 <4c> 39 c0 75 f4 e9 2b ff ff ff b8 01 00 00 00 48 83 c4 28 5b 5d 41
RSP: 0018:ffffc90000117300 EFLAGS: 00000006
RAX: ffffffff9770e2a8 RBX: 0000000000000001 RCX: 0000000000000001
RDX: 0000000000000111 RSI: 0000000000000001 RDI: ffffc900001173c0
RBP: 0000000000000030 R08: ffffffff95dd9b90 R09: 0000000000000001
R10: ffffc900001174a0 R11: 0000000000000000 R12: ffffffff81974ec0
R13: ffffc900001173a0 R14: ffffffff819759d0 R15: ffffc900001173c0
FS:  0000000000000000(0000) GS:ffff8881246b6000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555593ff75c8 CR3: 000000000e380000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 __bfs_backwards kernel/locking/lockdep.c:1860 [inline]
 check_irq_usage+0xcb/0x920 kernel/locking/lockdep.c:2796
 check_prev_add kernel/locking/lockdep.c:3169 [inline]
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x12bc/0x1ce0 kernel/locking/lockdep.c:5237
 lock_acquire kernel/locking/lockdep.c:5868 [inline]
 lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5825
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0x3a/0x60 kernel/locking/spinlock.c:162
 lock_hrtimer_base kernel/time/hrtimer.c:171 [inline]
 hrtimer_try_to_cancel+0xa9/0x2f0 kernel/time/hrtimer.c:1362
 update_curr_dl_se+0x42c/0xa10 kernel/sched/deadline.c:1468
 update_curr+0x3fb/0x550 kernel/sched/fair.c:1243
 pick_task_fair+0x171/0x330 kernel/sched/fair.c:8753
 pick_next_task_fair+0x20/0x1010 kernel/sched/fair.c:8778
 __pick_next_task+0xf1/0x6c0 kernel/sched/core.c:6001
 pick_next_task kernel/sched/core.c:6099 [inline]
 __schedule+0x5d3/0x5de0 kernel/sched/core.c:6902
 preempt_schedule_common+0x44/0xc0 kernel/sched/core.c:7145
 preempt_schedule_thunk+0x16/0x30 arch/x86/entry/thunk.S:12
 on_each_cpu_cond_mask+0x75/0x90 kernel/smp.c:1045
 on_each_cpu include/linux/smp.h:71 [inline]
 smp_text_poke_sync_each_cpu arch/x86/kernel/alternative.c:2653 [inline]
 smp_text_poke_batch_finish+0x7b4/0xdb0 arch/x86/kernel/alternative.c:2946
 arch_jump_label_transform_apply+0x1c/0x30 arch/x86/kernel/jump_label.c:146
 jump_label_update+0x376/0x550 kernel/jump_label.c:919
 static_key_enable_cpuslocked+0x1b7/0x270 kernel/jump_label.c:210
 static_key_enable+0x1a/0x20 kernel/jump_label.c:223
 toggle_allocation_gate mm/kfence/core.c:850 [inline]
 toggle_allocation_gate+0xfa/0x280 mm/kfence/core.c:842
 process_one_work+0x9cc/0x1b70 kernel/workqueue.c:3236
 process_scheduled_works kernel/workqueue.c:3319 [inline]
 worker_thread+0x6c8/0xf10 kernel/workqueue.c:3400
 kthread+0x3c2/0x780 kernel/kthread.c:463
 ret_from_fork+0x5d4/0x6f0 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>


Tested on:

commit:         d69eb204 Merge tag 'net-6.17-rc5' of git://git.kernel...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1551b162580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d4703ac89d9e185a
dashboard link: https://syzkaller.appspot.com/bug?extid=b73c7d94a151e2ee1e9b
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=13dd1312580000