[syzbot] [fs?] [mm?] INFO: task hung in v9fs_file_fsync

[syzbot <syzbot+d1b5dace43896bc386c3@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    038d61fd6422 Linux 6.16
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=15f5a234580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=515ec0b49771bcd1
dashboard link: https://syzkaller.appspot.com/bug?extid=d1b5dace43896bc386c3
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=158063a2580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1335d3a2580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/34e894532715/disk-038d61fd.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b6a27a46b9dc/vmlinux-038d61fd.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f97a9c8d8216/bzImage-038d61fd.xz

The issue was bisected to:

commit aaec5a95d59615523db03dd53c2052f0a87beea7
Author: Oleg Nesterov <oleg@redhat.com>
Date:   Thu Jan 2 14:07:15 2025 +0000

    pipe_read: don't wake up the writer if the pipe is still full

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1498e3a2580000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=1698e3a2580000
console output: https://syzkaller.appspot.com/x/log.txt?x=1298e3a2580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d1b5dace43896bc386c3@syzkaller.appspotmail.com
Fixes: aaec5a95d596 ("pipe_read: don't wake up the writer if the pipe is still full")

INFO: task syz-executor224:5849 blocked for more than 143 seconds.
      Not tainted 6.16.0-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor224 state:D stack:22952 pid:5849  tgid:5849  ppid:5848   task_flags:0x400140 flags:0x00004006
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5397 [inline]
 __schedule+0x16aa/0x4c90 kernel/sched/core.c:6786
 __schedule_loop kernel/sched/core.c:6864 [inline]
 schedule+0x165/0x360 kernel/sched/core.c:6879
 io_schedule+0x81/0xe0 kernel/sched/core.c:7724
 folio_wait_bit_common+0x6b0/0xb90 mm/filemap.c:1317
 folio_wait_writeback+0xb0/0x100 mm/page-writeback.c:3126
 __filemap_fdatawait_range+0x147/0x230 mm/filemap.c:539
 file_write_and_wait_range+0x275/0x330 mm/filemap.c:798
 v9fs_file_fsync+0xcf/0x1a0 fs/9p/vfs_file.c:418
 generic_write_sync include/linux/fs.h:3031 [inline]
 netfs_file_write_iter+0x3d8/0x4a0 fs/netfs/buffered_write.c:494
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x54b/0xa90 fs/read_write.c:686
 ksys_write+0x145/0x250 fs/read_write.c:738
 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: 0033:0x7fb29049bef9
RSP: 002b:00007ffeb3361588 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000200000000140 RCX: 00007fb29049bef9
RDX: 0000000000007fec RSI: 0000200000000300 RDI: 0000000000000007
RBP: 0030656c69662f2e R08: 0000000000000006 R09: 0000000000000006
R10: 0000000000000006 R11: 0000000000000246 R12: 0000200000000180
R13: 00007fb2904e504e R14: 0000000000000001 R15: 0000000000000001
 </TASK>

Showing all locks held in the system:
2 locks held by kworker/u8:0/12:
1 lock held by khungtaskd/31:
 #0: ffffffff8e13f0e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #0: ffffffff8e13f0e0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline]
 #0: ffffffff8e13f0e0 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180 kernel/locking/lockdep.c:6770
2 locks held by kworker/u8:6/1337:
 #0: ffff88801a489148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3213 [inline]
 #0: ffff88801a489148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_scheduled_works+0x9b4/0x17b0 kernel/workqueue.c:3321
 #1: ffffc9000451fbc0 ((work_completion)(&rreq->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3214 [inline]
 #1: ffffc9000451fbc0 ((work_completion)(&rreq->work)){+.+.}-{0:0}, at: process_scheduled_works+0x9ef/0x17b0 kernel/workqueue.c:3321
2 locks held by getty/5596:
 #0: ffff88803095f0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
 #1: ffffc900036cb2f0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x43e/0x1400 drivers/tty/n_tty.c:2222
1 lock held by syz-executor224/5849:
 #0: ffff88807f8cc428 (sb_writers#8){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:3096 [inline]
 #0: ffff88807f8cc428 (sb_writers#8){.+.+}-{0:0}, at: vfs_write+0x211/0xa90 fs/read_write.c:682

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

NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 31 Comm: khungtaskd Not tainted 6.16.0-syzkaller #0 PREEMPT(full) 
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:158 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:307 [inline]
 watchdog+0xfee/0x1030 kernel/hung_task.c:470
 kthread+0x70e/0x8a0 kernel/kthread.c:464
 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 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.16.0-syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
RIP: 0010:pv_native_safe_halt+0x13/0x20 arch/x86/kernel/paravirt.c:82
Code: 53 de 02 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 d3 ad 21 00 f3 0f 1e fa fb f4 <c3> cc cc cc cc cc cc cc cc cc cc cc cc 90 90 90 90 90 90 90 90 90
RSP: 0018:ffffffff8de07d80 EFLAGS: 000002c2
RAX: eefad1cde067ed00 RBX: ffffffff81976918 RCX: eefad1cde067ed00
RDX: 0000000000000001 RSI: ffffffff8d982fba RDI: ffffffff8be1ba40
RBP: ffffffff8de07ea8 R08: ffff8880b8632f5b R09: 1ffff110170c65eb
R10: dffffc0000000000 R11: ffffed10170c65ec R12: ffffffff8fa0b3f0
R13: 0000000000000000 R14: 0000000000000000 R15: 1ffffffff1bd2a50
FS:  0000000000000000(0000) GS:ffff888125c57000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055943a295660 CR3: 000000000df38000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 arch_safe_halt arch/x86/include/asm/paravirt.h:107 [inline]
 default_idle+0x13/0x20 arch/x86/kernel/process.c:749
 default_idle_call+0x74/0xb0 kernel/sched/idle.c:117
 cpuidle_idle_call kernel/sched/idle.c:185 [inline]
 do_idle+0x1e8/0x510 kernel/sched/idle.c:325
 cpu_startup_entry+0x44/0x60 kernel/sched/idle.c:423
 rest_init+0x2de/0x300 init/main.c:745
 start_kernel+0x47d/0x500 init/main.c:1102
 x86_64_start_reservations+0x24/0x30 arch/x86/kernel/head64.c:307
 x86_64_start_kernel+0x143/0x1c0 arch/x86/kernel/head64.c:288
 common_startup_64+0x13e/0x147
 </TASK>


---
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