Re: [syzbot] INFO: task hung in hci_req_sync

Hi Pavel,

quoted

syzbot found the following issue on:
HEAD commit:    c9194f32bfd9 Merge tag 'ext4_for_linus_stable' of git://gi..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1488f59e300000
kernel config:  https://syzkaller.appspot.com/x/.config?x=343fd21f6f4da2d6
dashboard link: https://syzkaller.appspot.com/bug?extid=be2baed593ea56c6a84c
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15b5afc6300000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15fcd192300000
Bisection is inconclusive: the issue happens on the oldest tested release.
bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=17dce4fa300000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=143ce4fa300000
console output: https://syzkaller.appspot.com/x/log.txt?x=103ce4fa300000
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+be2baed593ea56c6a84c@syzkaller.appspotmail.com
INFO: task syz-executor446:8489 blocked for more than 143 seconds.
      Not tainted 5.14.0-rc4-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor446 state:D stack:28712 pid: 8489 ppid:  8452 flags:0x00000000
Call Trace:
 context_switch kernel/sched/core.c:4683 [inline]
 __schedule+0x93a/0x26f0 kernel/sched/core.c:5940
 schedule+0xd3/0x270 kernel/sched/core.c:6019
 schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:6078
 __mutex_lock_common kernel/locking/mutex.c:1036 [inline]
 __mutex_lock+0x7b6/0x10a0 kernel/locking/mutex.c:1104
 hci_req_sync+0x33/0xd0 net/bluetooth/hci_request.c:276
 hci_inquiry+0x6f4/0x9e0 net/bluetooth/hci_core.c:1357
 hci_sock_ioctl+0x1a7/0x910 net/bluetooth/hci_sock.c:1060
 sock_do_ioctl+0xcb/0x2d0 net/socket.c:1094
 sock_ioctl+0x477/0x6a0 net/socket.c:1221
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:1069 [inline]
 __se_sys_ioctl fs/ioctl.c:1055 [inline]
 __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:1055
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x446449
RSP: 002b:00007f36ab8342e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004cb400 RCX: 0000000000446449
RDX: 00000000200000c0 RSI: 00000000800448f0 RDI: 0000000000000004
RBP: 00000000004cb40c R08: 0000000000000000 R09: 0000000000000000
R10: ffffffffffffffff R11: 0000000000000246 R12: 0000000000000003
R13: 0000000000000004 R14: 00007f36ab8346b8 R15: 00000000004cb408
INFO: task syz-executor446:8491 blocked for more than 143 seconds.
      Not tainted 5.14.0-rc4-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor446 state:D stack:28176 pid: 8491 ppid:  8452 flags:0x00000004
Call Trace:
 context_switch kernel/sched/core.c:4683 [inline]
 __schedule+0x93a/0x26f0 kernel/sched/core.c:5940
 schedule+0xd3/0x270 kernel/sched/core.c:6019
 schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:6078
 __mutex_lock_common kernel/locking/mutex.c:1036 [inline]
 __mutex_lock+0x7b6/0x10a0 kernel/locking/mutex.c:1104
 hci_req_sync+0x33/0xd0 net/bluetooth/hci_request.c:276
 hci_inquiry+0x6f4/0x9e0 net/bluetooth/hci_core.c:1357
 hci_sock_ioctl+0x1a7/0x910 net/bluetooth/hci_sock.c:1060
 sock_do_ioctl+0xcb/0x2d0 net/socket.c:1094
 sock_ioctl+0x477/0x6a0 net/socket.c:1221
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:1069 [inline]
 __se_sys_ioctl fs/ioctl.c:1055 [inline]
 __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:1055
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x446449
RSP: 002b:00007f36ab8342e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004cb400 RCX: 0000000000446449
RDX: 00000000200000c0 RSI: 00000000800448f0 RDI: 0000000000000004
RBP: 00000000004cb40c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003
R13: 0000000000000004 R14: 00007f36ab8346b8 R15: 00000000004cb408
Showing all locks held in the system:
6 locks held by kworker/u4:0/8:
1 lock held by khungtaskd/1635:
 #0: ffffffff8b97c180 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x53/0x260 kernel/locking/lockdep.c:6446
1 lock held by in:imklog/8352:
 #0: ffff888033e1d4f0 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0xe9/0x100 fs/file.c:974
1 lock held by syz-executor446/8486:
 #0: ffff8880349c4ff0 (&hdev->req_lock){+.+.}-{3:3}, at: hci_req_sync+0x33/0xd0 net/bluetooth/hci_request.c:276
1 lock held by syz-executor446/8489:
 #0: ffff8880349c4ff0 (&hdev->req_lock){+.+.}-{3:3}, at: hci_req_sync+0x33/0xd0 net/bluetooth/hci_request.c:276
1 lock held by syz-executor446/8491:
 #0: ffff8880349c4ff0 (&hdev->req_lock){+.+.}-{3:3}, at: hci_req_sync+0x33/0xd0 net/bluetooth/hci_request.c:276

Looks like too big timeout is passed from ioctl:


C repro:

   *(uint16_t*)0x200000c0 = 0;
   *(uint16_t*)0x200000c2 = 0;
   memcpy((void*)0x200000c4, "\xf0\x08\xa7", 3);
   *(uint8_t*)0x200000c7 = 0x81;	<- ir.length
   *(uint8_t*)0x200000c8 = 0;
   syscall(__NR_ioctl, r[0], 0x800448f0, 0x200000c0ul);


Then ir.length * msecs_to_jiffies(2000) timeout is passed to
hci_req_sync(). Task will stuck here

	err = wait_event_interruptible_timeout(hdev->req_wait_q,
			hdev->req_status != HCI_REQ_PEND, timeout);

for 258 seconds (I guess, it's because of test environment, but, maybe, we should add sanity check for timeout value)

I agree. Feel free to send a patch.

Regards

Marcel