[syzbot] possible deadlock in p9_write_work

[syzbot <syzbot+bde0f89deacca7c765b8@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    8515d05bf6bc Add linux-next specific files for 20220328
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=155abcc3700000
kernel config:  https://syzkaller.appspot.com/x/.config?x=530c68bef4e2b8a8
dashboard link: https://syzkaller.appspot.com/bug?extid=bde0f89deacca7c765b8
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

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

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+bde0f89deacca7c765b8@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
5.17.0-next-20220328-syzkaller #0 Not tainted
------------------------------------------------------
kworker/1:1/26 is trying to acquire lock:
ffff88807eece460 (sb_writers#3){.+.+}-{0:0}, at: p9_fd_write net/9p/trans_fd.c:428 [inline]
ffff88807eece460 (sb_writers#3){.+.+}-{0:0}, at: p9_write_work+0x25e/0xca0 net/9p/trans_fd.c:479

but task is already holding lock:
ffffc90000a1fda8 ((work_completion)(&m->wq)){+.+.}-{0:0}, at: process_one_work+0x8ae/0x1610 kernel/workqueue.c:2264

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 ((work_completion)(&m->wq)){+.+.}-{0:0}:
       process_one_work+0x905/0x1610 kernel/workqueue.c:2265
       worker_thread+0x665/0x1080 kernel/workqueue.c:2436
       kthread+0x2e9/0x3a0 kernel/kthread.c:376
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298

-> #2 ((wq_completion)events){+.+.}-{0:0}:
       flush_workqueue+0x164/0x1440 kernel/workqueue.c:2831
       flush_scheduled_work include/linux/workqueue.h:583 [inline]
       ext4_put_super+0x99/0x1150 fs/ext4/super.c:1202
       generic_shutdown_super+0x14c/0x400 fs/super.c:462
       kill_block_super+0x97/0xf0 fs/super.c:1394
       deactivate_locked_super+0x94/0x160 fs/super.c:332
       deactivate_super+0xad/0xd0 fs/super.c:363
       cleanup_mnt+0x3a2/0x540 fs/namespace.c:1186
       task_work_run+0xdd/0x1a0 kernel/task_work.c:164
       resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
       exit_to_user_mode_loop kernel/entry/common.c:183 [inline]
       exit_to_user_mode_prepare+0x23c/0x250 kernel/entry/common.c:215
       __syscall_exit_to_user_mode_work kernel/entry/common.c:297 [inline]
       syscall_exit_to_user_mode+0x19/0x60 kernel/entry/common.c:308
       do_syscall_64+0x42/0x80 arch/x86/entry/common.c:86
       entry_SYSCALL_64_after_hwframe+0x44/0xae

-> #1 (&type->s_umount_key#32){++++}-{3:3}:
       down_read+0x98/0x440 kernel/locking/rwsem.c:1461
       iterate_supers+0xdb/0x290 fs/super.c:692
       drop_caches_sysctl_handler+0xdb/0x110 fs/drop_caches.c:62
       proc_sys_call_handler+0x4a1/0x6e0 fs/proc/proc_sysctl.c:604
       call_write_iter include/linux/fs.h:2080 [inline]
       do_iter_readv_writev+0x3d1/0x640 fs/read_write.c:726
       do_iter_write+0x182/0x700 fs/read_write.c:852
       vfs_iter_write+0x70/0xa0 fs/read_write.c:893
       iter_file_splice_write+0x723/0xc70 fs/splice.c:689
       do_splice_from fs/splice.c:767 [inline]
       direct_splice_actor+0x110/0x180 fs/splice.c:936
       splice_direct_to_actor+0x34b/0x8c0 fs/splice.c:891
       do_splice_direct+0x1a7/0x270 fs/splice.c:979
       do_sendfile+0xae0/0x1240 fs/read_write.c:1246
       __do_sys_sendfile64 fs/read_write.c:1305 [inline]
       __se_sys_sendfile64 fs/read_write.c:1297 [inline]
       __x64_sys_sendfile64+0x149/0x210 fs/read_write.c:1297
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x35/0x80 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x44/0xae

-> #0 (sb_writers#3){.+.+}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3096 [inline]
       check_prevs_add kernel/locking/lockdep.c:3219 [inline]
       validate_chain kernel/locking/lockdep.c:3834 [inline]
       __lock_acquire+0x2ac6/0x56c0 kernel/locking/lockdep.c:5060
       lock_acquire kernel/locking/lockdep.c:5672 [inline]
       lock_acquire+0x1ab/0x510 kernel/locking/lockdep.c:5637
       percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
       __sb_start_write include/linux/fs.h:1728 [inline]
       sb_start_write include/linux/fs.h:1798 [inline]
       file_start_write include/linux/fs.h:2815 [inline]
       kernel_write fs/read_write.c:564 [inline]
       kernel_write+0x2ac/0x540 fs/read_write.c:555
       p9_fd_write net/9p/trans_fd.c:428 [inline]
       p9_write_work+0x25e/0xca0 net/9p/trans_fd.c:479
       process_one_work+0x996/0x1610 kernel/workqueue.c:2289
       worker_thread+0x665/0x1080 kernel/workqueue.c:2436
       kthread+0x2e9/0x3a0 kernel/kthread.c:376
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298

other info that might help us debug this:

Chain exists of:
  sb_writers#3 --> (wq_completion)events --> (work_completion)(&m->wq)

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock((work_completion)(&m->wq));
                               lock((wq_completion)events);
                               lock((work_completion)(&m->wq));
  lock(sb_writers#3);

 *** DEADLOCK ***

2 locks held by kworker/1:1/26:
 #0: ffff888010c64d38 ((wq_completion)events){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
 #0: ffff888010c64d38 ((wq_completion)events){+.+.}-{0:0}, at: arch_atomic_long_set include/linux/atomic/atomic-long.h:41 [inline]
 #0: ffff888010c64d38 ((wq_completion)events){+.+.}-{0:0}, at: atomic_long_set include/linux/atomic/atomic-instrumented.h:1280 [inline]
 #0: ffff888010c64d38 ((wq_completion)events){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:636 [inline]
 #0: ffff888010c64d38 ((wq_completion)events){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:663 [inline]
 #0: ffff888010c64d38 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x87a/0x1610 kernel/workqueue.c:2260
 #1: ffffc90000a1fda8 ((work_completion)(&m->wq)){+.+.}-{0:0}, at: process_one_work+0x8ae/0x1610 kernel/workqueue.c:2264

stack backtrace:
CPU: 1 PID: 26 Comm: kworker/1:1 Not tainted 5.17.0-next-20220328-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events p9_write_work
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
 check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2176
 check_prev_add kernel/locking/lockdep.c:3096 [inline]
 check_prevs_add kernel/locking/lockdep.c:3219 [inline]
 validate_chain kernel/locking/lockdep.c:3834 [inline]
 __lock_acquire+0x2ac6/0x56c0 kernel/locking/lockdep.c:5060
 lock_acquire kernel/locking/lockdep.c:5672 [inline]
 lock_acquire+0x1ab/0x510 kernel/locking/lockdep.c:5637
 percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
 __sb_start_write include/linux/fs.h:1728 [inline]
 sb_start_write include/linux/fs.h:1798 [inline]
 file_start_write include/linux/fs.h:2815 [inline]
 kernel_write fs/read_write.c:564 [inline]
 kernel_write+0x2ac/0x540 fs/read_write.c:555
 p9_fd_write net/9p/trans_fd.c:428 [inline]
 p9_write_work+0x25e/0xca0 net/9p/trans_fd.c:479
 process_one_work+0x996/0x1610 kernel/workqueue.c:2289
 worker_thread+0x665/0x1080 kernel/workqueue.c:2436
 kthread+0x2e9/0x3a0 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298
 </TASK>
usb 4-1: new high-speed USB device number 72 using dummy_hcd
usb 4-1: New USB device found, idVendor=1b3d, idProduct=0193, bcdDevice= 8.4d
usb 4-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
usb 4-1: config 0 descriptor??
ftdi_sio 4-1:0.0: FTDI USB Serial Device converter detected
usb 4-1: Detected FT232RL
ftdi_sio ttyUSB0: Unable to read latency timer: -71
ftdi_sio ttyUSB0: Unable to write latency timer: -71
ftdi_sio 4-1:0.0: GPIO initialisation failed: -71
usb 4-1: FTDI USB Serial Device converter now attached to ttyUSB0
usb 4-1: USB disconnect, device number 72
ftdi_sio ttyUSB0: FTDI USB Serial Device converter now disconnected from ttyUSB0
ftdi_sio 4-1:0.0: device disconnected
usb 4-1: new high-speed USB device number 73 using dummy_hcd
usb 4-1: New USB device found, idVendor=1b3d, idProduct=0193, bcdDevice= 8.4d
usb 4-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
usb 4-1: config 0 descriptor??
ftdi_sio 4-1:0.0: FTDI USB Serial Device converter detected
usb 4-1: Detected FT232RL
ftdi_sio ttyUSB0: Unable to read latency timer: -71
ftdi_sio ttyUSB0: Unable to write latency timer: -71
ftdi_sio 4-1:0.0: GPIO initialisation failed: -71
usb 4-1: FTDI USB Serial Device converter now attached to ttyUSB0
usb 4-1: USB disconnect, device number 73
ftdi_sio ttyUSB0: FTDI USB Serial Device converter now disconnected from ttyUSB0
ftdi_sio 4-1:0.0: device disconnected


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