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    SubjectRe: possible deadlock in iowarrior_open
    On Thu, Aug 1, 2019 at 5:28 PM syzbot
    <syzbot+ca52394faa436d8131df@syzkaller.appspotmail.com> wrote:
    >
    > Hello,
    >
    > syzbot found the following crash on:
    >
    > HEAD commit: 7f7867ff usb-fuzzer: main usb gadget fuzzer driver
    > git tree: https://github.com/google/kasan.git usb-fuzzer
    > console output: https://syzkaller.appspot.com/x/log.txt?x=17ab6aec600000
    > kernel config: https://syzkaller.appspot.com/x/.config?x=792eb47789f57810
    > dashboard link: https://syzkaller.appspot.com/bug?extid=ca52394faa436d8131df
    > compiler: gcc (GCC) 9.0.0 20181231 (experimental)
    >
    > Unfortunately, I don't have any reproducer for this crash yet.
    >
    > IMPORTANT: if you fix the bug, please add the following tag to the commit:
    > Reported-by: syzbot+ca52394faa436d8131df@syzkaller.appspotmail.com
    >
    > ======================================================
    > WARNING: possible circular locking dependency detected
    > 5.3.0-rc2+ #23 Not tainted
    > ------------------------------------------------------
    > syz-executor.0/10062 is trying to acquire lock:
    > 00000000527cb8c7 (iowarrior_open_disc_lock){+.+.}, at:
    > iowarrior_open+0x8a/0x2a0 drivers/usb/misc/iowarrior.c:600
    >
    > but task is already holding lock:
    > 0000000061445bc7 (iowarrior_mutex){+.+.}, at: iowarrior_open+0x23/0x2a0
    > drivers/usb/misc/iowarrior.c:589
    >
    > which lock already depends on the new lock.
    >
    >
    > the existing dependency chain (in reverse order) is:
    >
    > -> #2 (iowarrior_mutex){+.+.}:
    > __mutex_lock_common kernel/locking/mutex.c:930 [inline]
    > __mutex_lock+0x158/0x1360 kernel/locking/mutex.c:1077
    > iowarrior_open+0x23/0x2a0 drivers/usb/misc/iowarrior.c:589
    > usb_open+0x1df/0x270 drivers/usb/core/file.c:48
    > chrdev_open+0x219/0x5c0 fs/char_dev.c:414
    > do_dentry_open+0x494/0x1120 fs/open.c:797
    > do_last fs/namei.c:3416 [inline]
    > path_openat+0x1430/0x3f50 fs/namei.c:3533
    > do_filp_open+0x1a1/0x280 fs/namei.c:3563
    > do_sys_open+0x3c0/0x580 fs/open.c:1089
    > do_syscall_64+0xb7/0x580 arch/x86/entry/common.c:296
    > entry_SYSCALL_64_after_hwframe+0x49/0xbe
    >
    > -> #1 (minor_rwsem#2){++++}:
    > down_write+0x92/0x150 kernel/locking/rwsem.c:1500
    > usb_deregister_dev drivers/usb/core/file.c:238 [inline]
    > usb_deregister_dev+0x61/0x270 drivers/usb/core/file.c:230
    > iowarrior_disconnect+0xa8/0x2c0 drivers/usb/misc/iowarrior.c:873
    > usb_unbind_interface+0x1bd/0x8a0 drivers/usb/core/driver.c:423
    > __device_release_driver drivers/base/dd.c:1120 [inline]
    > device_release_driver_internal+0x404/0x4c0 drivers/base/dd.c:1151
    > bus_remove_device+0x2dc/0x4a0 drivers/base/bus.c:556
    > device_del+0x420/0xb10 drivers/base/core.c:2288
    > usb_disable_device+0x211/0x690 drivers/usb/core/message.c:1237
    > usb_disconnect+0x284/0x8d0 drivers/usb/core/hub.c:2199
    > hub_port_connect drivers/usb/core/hub.c:4949 [inline]
    > hub_port_connect_change drivers/usb/core/hub.c:5213 [inline]
    > port_event drivers/usb/core/hub.c:5359 [inline]
    > hub_event+0x1454/0x3640 drivers/usb/core/hub.c:5441
    > process_one_work+0x92b/0x1530 kernel/workqueue.c:2269
    > worker_thread+0x96/0xe20 kernel/workqueue.c:2415
    > kthread+0x318/0x420 kernel/kthread.c:255
    > ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
    >
    > -> #0 (iowarrior_open_disc_lock){+.+.}:
    > check_prev_add kernel/locking/lockdep.c:2405 [inline]
    > check_prevs_add kernel/locking/lockdep.c:2507 [inline]
    > validate_chain kernel/locking/lockdep.c:2897 [inline]
    > __lock_acquire+0x1f7c/0x3b50 kernel/locking/lockdep.c:3880
    > lock_acquire+0x127/0x320 kernel/locking/lockdep.c:4412
    > __mutex_lock_common kernel/locking/mutex.c:930 [inline]
    > __mutex_lock+0x158/0x1360 kernel/locking/mutex.c:1077
    > iowarrior_open+0x8a/0x2a0 drivers/usb/misc/iowarrior.c:600
    > usb_open+0x1df/0x270 drivers/usb/core/file.c:48
    > chrdev_open+0x219/0x5c0 fs/char_dev.c:414
    > do_dentry_open+0x494/0x1120 fs/open.c:797
    > do_last fs/namei.c:3416 [inline]
    > path_openat+0x1430/0x3f50 fs/namei.c:3533
    > do_filp_open+0x1a1/0x280 fs/namei.c:3563
    > do_sys_open+0x3c0/0x580 fs/open.c:1089
    > do_syscall_64+0xb7/0x580 arch/x86/entry/common.c:296
    > entry_SYSCALL_64_after_hwframe+0x49/0xbe
    >
    > other info that might help us debug this:
    >
    > Chain exists of:
    > iowarrior_open_disc_lock --> minor_rwsem#2 --> iowarrior_mutex
    >
    > Possible unsafe locking scenario:
    >
    > CPU0 CPU1
    > ---- ----
    > lock(iowarrior_mutex);
    > lock(minor_rwsem#2);
    > lock(iowarrior_mutex);
    > lock(iowarrior_open_disc_lock);
    >
    > *** DEADLOCK ***
    >
    > 2 locks held by syz-executor.0/10062:
    > #0: 000000000fd8903d (minor_rwsem#2){++++}, at: usb_open+0x23/0x270
    > drivers/usb/core/file.c:39
    > #1: 0000000061445bc7 (iowarrior_mutex){+.+.}, at:
    > iowarrior_open+0x23/0x2a0 drivers/usb/misc/iowarrior.c:589
    >
    > stack backtrace:
    > CPU: 0 PID: 10062 Comm: syz-executor.0 Not tainted 5.3.0-rc2+ #23
    > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
    > Google 01/01/2011
    > Call Trace:
    > __dump_stack lib/dump_stack.c:77 [inline]
    > dump_stack+0xca/0x13e lib/dump_stack.c:113
    > check_noncircular+0x345/0x3e0 kernel/locking/lockdep.c:1741
    > check_prev_add kernel/locking/lockdep.c:2405 [inline]
    > check_prevs_add kernel/locking/lockdep.c:2507 [inline]
    > validate_chain kernel/locking/lockdep.c:2897 [inline]
    > __lock_acquire+0x1f7c/0x3b50 kernel/locking/lockdep.c:3880
    > lock_acquire+0x127/0x320 kernel/locking/lockdep.c:4412
    > __mutex_lock_common kernel/locking/mutex.c:930 [inline]
    > __mutex_lock+0x158/0x1360 kernel/locking/mutex.c:1077
    > iowarrior_open+0x8a/0x2a0 drivers/usb/misc/iowarrior.c:600
    > usb_open+0x1df/0x270 drivers/usb/core/file.c:48
    > chrdev_open+0x219/0x5c0 fs/char_dev.c:414
    > do_dentry_open+0x494/0x1120 fs/open.c:797
    > do_last fs/namei.c:3416 [inline]
    > path_openat+0x1430/0x3f50 fs/namei.c:3533
    > do_filp_open+0x1a1/0x280 fs/namei.c:3563
    > do_sys_open+0x3c0/0x580 fs/open.c:1089
    > do_syscall_64+0xb7/0x580 arch/x86/entry/common.c:296
    > entry_SYSCALL_64_after_hwframe+0x49/0xbe
    > RIP: 0033:0x413711
    > Code: 75 14 b8 02 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 04 19 00 00 c3 48
    > 83 ec 08 e8 0a fa ff ff 48 89 04 24 b8 02 00 00 00 0f 05 <48> 8b 3c 24 48
    > 89 c2 e8 53 fa ff ff 48 89 d0 48 83 c4 08 48 3d 01
    > RSP: 002b:00007fbd98b927a0 EFLAGS: 00000293 ORIG_RAX: 0000000000000002
    > RAX: ffffffffffffffda RBX: 6666666666666667 RCX: 0000000000413711
    > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00007fbd98b92850
    > RBP: 000000000075bf20 R08: 000000000000000f R09: 0000000000000000
    > R10: 0000000000000000 R11: 0000000000000293 R12: 00007fbd98b936d4
    > R13: 00000000004c8bee R14: 00000000004dfa68 R15: 00000000ffffffff

    #syz dup: possible deadlock in usb_deregister_dev

    >
    >
    > ---
    > This bug is generated by a bot. It may contain errors.
    > See https://goo.gl/tpsmEJ for more information about syzbot.
    > syzbot engineers can be reached at syzkaller@googlegroups.com.
    >
    > syzbot will keep track of this bug report. See:
    > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

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