WARNING in blk_mq_sched_free_requests (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    574cc453 Merge tag 'drm-next-2019-09-18' of git://anongit...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=167c3c7e600000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4c1d6bfa784bebea
dashboard link: https://syzkaller.appspot.com/bug?extid=da3b7677bb913dc1b737
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+da3b7677bb913dc1b737@xxxxxxxxxxxxxxxxxxxxxxxxx

------------[ cut here ]------------
WARNING: CPU: 1 PID: 9291 at block/blk-mq-sched.c:558  
blk_mq_sched_free_requests.cold+0x11/0x21 block/blk-mq-sched.c:558
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 9291 Comm: syz-executor.1 Not tainted 5.3.0+ #0
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+0x172/0x1f0 lib/dump_stack.c:113
 panic+0x2dc/0x755 kernel/panic.c:219
 __warn.cold+0x20/0x4c kernel/panic.c:576
 report_bug+0x263/0x2b0 lib/bug.c:186
 fixup_bug arch/x86/kernel/traps.c:179 [inline]
 fixup_bug arch/x86/kernel/traps.c:174 [inline]
 do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:272
 do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:291
 invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1028
RIP: 0010:blk_mq_sched_free_requests.cold+0x11/0x21 block/blk-mq-sched.c:558
Code: fe 45 85 f6 0f 84 ab e9 ff ff e9 29 e8 ff ff 48 89 cf e8 43 0e 7d fe  
eb ce e8 bc c3 42 fe 48 c7 c7 00 65 e5 87 e8 84 47 2c fe <0f> 0b e9 47 f3  
ff ff 90 90 90 90 90 90 90 90 90 55 48 89 e5 41 57
RSP: 0018:ffff88805aa6f9e0 EFLAGS: 00010286
RAX: 0000000000000024 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff815c26d6 RDI: ffffed100b54df2e
RBP: ffff88805aa6fa30 R08: 0000000000000024 R09: ffffed1015d260d1
R10: ffffed1015d260d0 R11: ffff8880ae930687 R12: 00000000fffffff4
R13: ffff8880a3100100 R14: ffff88808521e1d8 R15: ffff8880a3100100
 blk_mq_init_sched+0x32c/0x766 block/blk-mq-sched.c:543
 elevator_init_mq+0x1d3/0x3f0 block/elevator.c:719
 __device_add_disk+0xd57/0x1230 block/genhd.c:705
 device_add_disk+0x2b/0x40 block/genhd.c:763
 add_disk include/linux/genhd.h:429 [inline]
 loop_add+0x635/0x8d0 drivers/block/loop.c:2051
 loop_control_ioctl drivers/block/loop.c:2152 [inline]
 loop_control_ioctl+0x165/0x360 drivers/block/loop.c:2134
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:509 [inline]
 do_vfs_ioctl+0xdb6/0x13e0 fs/ioctl.c:696
 ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
 __do_sys_ioctl fs/ioctl.c:720 [inline]
 __se_sys_ioctl fs/ioctl.c:718 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
 do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x459a09
Code: fd b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7  
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 cb b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f4830110c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000459a09
RDX: 0000000000000000 RSI: 0000000000004c80 RDI: 0000000000000005
RBP: 000000000075c118 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f48301116d4
R13: 00000000004c3118 R14: 00000000004d69f8 R15: 00000000ffffffff
Kernel Offset: disabled
Rebooting in 86400 seconds..


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