bisecting fixing commit since 893af1c79e42e53af0da22165b46eea135af0613
building syzkaller on 8fd428a197f1ff27bdb6d3d359745e2756133d01
testing commit 893af1c79e42e53af0da22165b46eea135af0613 with gcc (GCC) 8.1.0
kernel signature: b8488338a27220e6d1fdefb6833406e3e1e9887ed36d3bdf0492ddd22eb033eb
all runs: crashed: WARNING in loop_add
testing current HEAD d18b78abc0c6e7d3119367c931c583e02d466495
testing commit d18b78abc0c6e7d3119367c931c583e02d466495 with gcc (GCC) 8.1.0
kernel signature: 813bca23f0d4ba2e2abaf3cd3670ab5484e57b3fcddd79932ee5634842555262
all runs: crashed: WARNING in loop_add
revisions tested: 2, total time: 27m47.174243289s (build: 19m17.069764201s, test: 6m48.193963727s)
the crash still happens on HEAD
commit msg: Linux 4.19.141
crash: WARNING in loop_add
RDX: 0000000000000000 RSI: 0000000000004c80 RDI: 0000000000000003
RBP: 000000000075bfc8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f686933b6d4
R13: 00000000004c2fc7 R14: 00000000004d66c8 R15: 0000000000000004
------------[ cut here ]------------
WARNING: CPU: 0 PID: 7842 at block/genhd.c:709 __device_add_disk.cold.31+0x97/0xe5 block/genhd.c:709
Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 7842 Comm: syz-executor.5 Not tainted 4.19.141-syzkaller #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+0x123/0x177 lib/dump_stack.c:118
 panic+0x1cd/0x375 kernel/panic.c:186
 __warn.cold.8+0x1b/0x3e kernel/panic.c:541
 report_bug+0x1a4/0x200 lib/bug.c:186
 fixup_bug arch/x86/kernel/traps.c:178 [inline]
 do_error_trap+0x200/0x350 arch/x86/kernel/traps.c:296
 do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:316
 invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:1038
RIP: 0010:__device_add_disk.cold.31+0x97/0xe5 block/genhd.c:709
Code: fe eb e7 3c 03 7f 0c 48 8b bd 30 ff ff ff e8 a7 77 aa fe 8b 83 b8 05 00 00 e9 c8 d8 ff ff 48 c7 c7 60 f9 1d 87 e8 20 56 67 fe <0f> 0b e9 3a e2 ff ff 48 8d 73 0c 48 c7 c7 40 00 1e 87 e8 09 56 67
RSP: 0018:ffff888072737b10 EFLAGS: 00010282
RAX: 0000000000000024 RBX: ffff88809357ad80 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff871f4640 RDI: ffffffff89c926a0
RBP: ffff888072737c10 R08: ffffed1015d45079 R09: ffffed1015d45078
R10: ffffed1015d45078 R11: ffff8880aea283c7 R12: ffff88809357ae10
R13: ffff88809357b3d8 R14: ffff88809357ad84 R15: 0000000000000000
 device_add_disk+0xe/0x10 block/genhd.c:729
 add_disk include/linux/genhd.h:408 [inline]
 loop_add+0x595/0x7f0 drivers/block/loop.c:2045
 loop_control_ioctl+0x105/0x280 drivers/block/loop.c:2146
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:501 [inline]
 do_vfs_ioctl+0x196/0x10c0 fs/ioctl.c:688
 ksys_ioctl+0x62/0x90 fs/ioctl.c:705
 __do_sys_ioctl fs/ioctl.c:712 [inline]
 __se_sys_ioctl fs/ioctl.c:710 [inline]
 __x64_sys_ioctl+0x6e/0xb0 fs/ioctl.c:710
 do_syscall_64+0xd0/0x4e0 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4598a9
Code: 7d 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 4b b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f686933ac78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f686933ac90 RCX: 00000000004598a9
RDX: 0000000000000000 RSI: 0000000000004c80 RDI: 0000000000000003
RBP: 000000000075bfc8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f686933b6d4
R13: 00000000004c2fc7 R14: 00000000004d66c8 R15: 0000000000000004
Kernel Offset: disabled
Rebooting in 86400 seconds..