general protection fault in __loop_clr_fd

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    770fbb32 Add linux-next specific files for 20200228
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=103aee2de00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=576314276bce4ad5
dashboard link: https://syzkaller.appspot.com/bug?extid=3967212746d25888b189
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12fc670de00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+3967212746d25888b189@xxxxxxxxxxxxxxxxxxxxxxxxx

general protection fault, probably for non-canonical address 0xdffffc0000000021: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000108-0x000000000000010f]
CPU: 1 PID: 9504 Comm: syz-executor.1 Not tainted 5.6.0-rc3-next-20200228-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:workqueue_sysfs_unregister kernel/workqueue.c:5691 [inline]
RIP: 0010:destroy_workqueue+0x2e/0x6b0 kernel/workqueue.c:4351
Code: 49 89 fe 41 55 41 54 55 53 48 83 ec 08 e8 8a 6a 26 00 49 8d be 08 01 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 e0 05 00 00 49 8b 9e 08 01 00 00 48 85 db 74 19
RSP: 0018:ffffc90002277cc8 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: 0000000000000002 RCX: 0000000000000000
RDX: 0000000000000021 RSI: ffffffff814c2af6 RDI: 0000000000000108
RBP: ffff888218af18f0 R08: ffff88809880e480 R09: fffffbfff185270a
R10: fffffbfff1852709 R11: ffffffff8c29384f R12: ffff888218af1800
R13: ffff888218af1804 R14: 0000000000000000 R15: 0000000000004c01
FS:  00000000027e1940(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fa010a7d000 CR3: 0000000088d30000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 loop_unprepare_queue drivers/block/loop.c:891 [inline]
 __loop_clr_fd+0x185/0x1280 drivers/block/loop.c:1210
 loop_clr_fd drivers/block/loop.c:1335 [inline]
 lo_ioctl+0x2b4/0x1460 drivers/block/loop.c:1704
 __blkdev_driver_ioctl block/ioctl.c:321 [inline]
 blkdev_ioctl+0x25b/0x660 block/ioctl.c:717
 block_ioctl+0xe9/0x130 fs/block_dev.c:1983
 vfs_ioctl fs/ioctl.c:47 [inline]
 ksys_ioctl+0x11a/0x180 fs/ioctl.c:763
 __do_sys_ioctl fs/ioctl.c:772 [inline]
 __se_sys_ioctl fs/ioctl.c:770 [inline]
 __x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:770
 do_syscall_64+0xf6/0x790 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45c317
Code: 48 83 c4 08 48 89 d8 5b 5d c3 66 0f 1f 84 00 00 00 00 00 48 89 e8 48 f7 d8 48 39 c3 0f 92 c0 eb 92 66 90 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 0f 83 0d b8 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffd75653418 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045c317
RDX: 0000000000000000 RSI: 0000000000004c01 RDI: 0000000000000003
RBP: 0000000000000002 R08: 0000000000000000 R09: 000000000000000a
R10: 0000000000000075 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffd75653450 R14: 0000000000016fbc R15: 00007ffd75653460
Modules linked in:
---[ end trace 4ad871aadd3b1dba ]---
RIP: 0010:workqueue_sysfs_unregister kernel/workqueue.c:5691 [inline]
RIP: 0010:destroy_workqueue+0x2e/0x6b0 kernel/workqueue.c:4351
Code: 49 89 fe 41 55 41 54 55 53 48 83 ec 08 e8 8a 6a 26 00 49 8d be 08 01 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 e0 05 00 00 49 8b 9e 08 01 00 00 48 85 db 74 19
RSP: 0018:ffffc90002277cc8 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: 0000000000000002 RCX: 0000000000000000
RDX: 0000000000000021 RSI: ffffffff814c2af6 RDI: 0000000000000108
RBP: ffff888218af18f0 R08: ffff88809880e480 R09: fffffbfff185270a
R10: fffffbfff1852709 R11: ffffffff8c29384f R12: ffff888218af1800
R13: ffff888218af1804 R14: 0000000000000000 R15: 0000000000004c01
FS:  00000000027e1940(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f692de4b110 CR3: 0000000088d30000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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