general protection fault in relay_switch_subbuf (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    70f4b4ac Add linux-next specific files for 20190730
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=107f7fc8600000
kernel config:  https://syzkaller.appspot.com/x/.config?x=83083aa18c7fa5ce
dashboard link: https://syzkaller.appspot.com/bug?extid=c6e6fb9765b1f884106a
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+c6e6fb9765b1f884106a@xxxxxxxxxxxxxxxxxxxxxxxxx

kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 6341 Comm: syz-executor.1 Not tainted 5.3.0-rc2-next-20190730  
#55
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:relay_switch_subbuf+0x216/0x920 kernel/relay.c:755
Code: 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 bc 06 00 00 48 b8 00 00 00 00  
00 fc ff df 4c 8b 7b 58 49 8d 7f 50 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f  
85 7d 06 00 00 48 ba 00 00 00 00 00 fc ff df 49 8b
RSP: 0018:ffff888087a17568 EFLAGS: 00010006
RAX: dffffc0000000000 RBX: ffff88808a6cb840 RCX: ffffc9000816e000
RDX: 000000000000000a RSI: ffffffff8172d57e RDI: 0000000000000050
RBP: ffff888087a175c0 R08: ffff8880601522c0 R09: 0000000000000010
R10: ffffed1010f42eb6 R11: 0000000000000003 R12: 0000000000000040
R13: 0000000000000000 R14: ffff88809f376dc0 R15: 0000000000000000
FS:  00007eff1049a700(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000009797e000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 relay_reserve include/linux/relay.h:261 [inline]
 trace_note.isra.0+0x5b8/0x6e0 kernel/trace/blktrace.c:93
 trace_note_tsk kernel/trace/blktrace.c:124 [inline]
 __blk_add_trace+0xb70/0xe10 kernel/trace/blktrace.c:264
 blk_add_trace_bio.isra.0+0x19c/0x220 kernel/trace/blktrace.c:865
 blk_add_trace_bio_queue+0x46/0x60 kernel/trace/blktrace.c:902
 trace_block_bio_queue include/trace/events/block.h:357 [inline]
 generic_make_request_checks+0x16c3/0x21a0 block/blk-core.c:954
 generic_make_request+0x8f/0xb50 block/blk-core.c:1006
 submit_bio+0x104/0x4d0 block/blk-core.c:1163
 submit_bh_wbc+0x6b6/0x900 fs/buffer.c:3132
 submit_bh fs/buffer.c:3138 [inline]
 __bread_slow fs/buffer.c:1214 [inline]
 __bread_gfp+0x164/0x370 fs/buffer.c:1396
 sb_bread include/linux/buffer_head.h:307 [inline]
 fat_fill_super+0x353/0x3880 fs/fat/inode.c:1653
 vfat_fill_super+0x32/0x40 fs/fat/namei_vfat.c:1050
 mount_bdev+0x304/0x3c0 fs/super.c:1405
 vfat_mount+0x35/0x40 fs/fat/namei_vfat.c:1057
 legacy_get_tree+0x113/0x220 fs/fs_context.c:651
 vfs_get_tree+0x8f/0x380 fs/super.c:1480
 do_new_mount fs/namespace.c:2791 [inline]
 do_mount+0x13b3/0x1c30 fs/namespace.c:3111
 ksys_mount+0xdb/0x150 fs/namespace.c:3320
 __do_sys_mount fs/namespace.c:3334 [inline]
 __se_sys_mount fs/namespace.c:3331 [inline]
 __x64_sys_mount+0xbe/0x150 fs/namespace.c:3331
 do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45c27a
Code: b8 a6 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 9d 8d fb ff c3 66 2e 0f  
1f 84 00 00 00 00 00 66 90 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 7a 8d fb ff c3 66 0f 1f 84 00 00 00 00 00
RSP: 002b:00007eff10499a88 EFLAGS: 00000206 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007eff10499b40 RCX: 000000000045c27a
RDX: 00007eff10499ae0 RSI: 00000000200002c0 RDI: 00007eff10499b00
RBP: 0000000000000000 R08: 00007eff10499b40 R09: 00007eff10499ae0
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000003
R13: 00000000004c8a98 R14: 00000000004df8d0 R15: 00000000ffffffff
Modules linked in:
---[ end trace 04681dc2b7471884 ]---
RIP: 0010:relay_switch_subbuf+0x216/0x920 kernel/relay.c:755
Code: 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 bc 06 00 00 48 b8 00 00 00 00  
00 fc ff df 4c 8b 7b 58 49 8d 7f 50 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f  
85 7d 06 00 00 48 ba 00 00 00 00 00 fc ff df 49 8b
RSP: 0018:ffff888087a17568 EFLAGS: 00010006
RAX: dffffc0000000000 RBX: ffff88808a6cb840 RCX: ffffc9000816e000
RDX: 000000000000000a RSI: ffffffff8172d57e RDI: 0000000000000050
RBP: ffff888087a175c0 R08: ffff8880601522c0 R09: 0000000000000010
R10: ffffed1010f42eb6 R11: 0000000000000003 R12: 0000000000000040
R13: 0000000000000000 R14: ffff88809f376dc0 R15: 0000000000000000
FS:  00007eff1049a700(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000009797e000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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