BUG: unable to handle kernel paging request in __sb_start

BUG: unable to handle kernel paging request in __sb_start_write
Status: upstream: reported C repro on 2020/09/08 14:19
Reported-by: syzbot+4d428ef55ad3356698bf@syzkaller.appspotmail.com
First crash: 24d, last: 24d

Cause bisection: the issue happens on the oldest tested release (bisect log)
Crash: WARNING in sysfs_warn_dup (log)
Repro: C syz .config

Sample crash report:

BUG: unable to handle page fault for address: ffffe8ffffc33c70
#PF: supervisor write access in kernel mode
#PF: error_code(0x0002) - not-present page
PGD 77000000000000 P4D 77000000000000 
Oops: 0002 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 10445 Comm: syz-executor899 Not tainted 5.9.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:percpu_down_read_trylock include/linux/percpu-rwsem.h:82 [inline]
RIP: 0010:__sb_start_write+0x16e/0x470 fs/super.c:1674
Code: 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 e3 02 00 00 41 bd 01 00 00 00 bd 01 00 00 00 48 8b 43 68 <65> ff 00 e8 aa 6b b4 ff bf 01 00 00 00 e8 e0 d5 8f ff 31 ff 65 44
RSP: 0018:ffffc9000a0bfab8 EFLAGS: 00010246
RAX: 0000607f51633c70 RBX: ffff888098be2380 RCX: ffffffff81bfdf07
RDX: 1ffff1101317c47d RSI: 0000000000000001 RDI: ffff888098be23e8
RBP: 0000000000000001 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
R13: 0000000000000001 R14: 0000000000000000 R15: ffff8880854bc0b0
FS:  00007fa632ef6700(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffe8ffffc33c70 CR3: 000000000011b000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 sb_start_write_trylock include/linux/fs.h:1648 [inline]
 touch_atime+0x152/0x370 fs/inode.c:1831
 file_accessed include/linux/fs.h:2206 [inline]
 splice_direct_to_actor+0x762/0x980 fs/splice.c:989
 do_splice_direct+0x1b3/0x280 fs/splice.c:1059
 do_sendfile+0x55f/0xd40 fs/read_write.c:1540
 __do_sys_sendfile64 fs/read_write.c:1601 [inline]
 __se_sys_sendfile64 fs/read_write.c:1587 [inline]
 __x64_sys_sendfile64+0x1cc/0x210 fs/read_write.c:1587
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x446ac9
Code: Bad RIP value.
RSP: 002b:00007fa632ef5d18 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00000000006dbc58 RCX: 0000000000446ac9
RDX: 0000000000000000 RSI: 0000000000000005 RDI: 0000000000000004
RBP: 00000000006dbc50 R08: 65732f636f72702f R09: 65732f636f72702f
R10: 0800000080004101 R11: 0000000000000246 R12: 00000000006dbc5c
R13: 00007fa632ef5d20 R14: 00007fa632ef5d20 R15: 20c49ba5e353f7cf
Modules linked in:
CR2: ffffe8ffffc33c70
---[ end trace 641e2e487fb96738 ]---
RIP: 0010:percpu_down_read_trylock include/linux/percpu-rwsem.h:82 [inline]
RIP: 0010:__sb_start_write+0x16e/0x470 fs/super.c:1674
Code: 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 e3 02 00 00 41 bd 01 00 00 00 bd 01 00 00 00 48 8b 43 68 <65> ff 00 e8 aa 6b b4 ff bf 01 00 00 00 e8 e0 d5 8f ff 31 ff 65 44
RSP: 0018:ffffc9000a0bfab8 EFLAGS: 00010246
RAX: 0000607f51633c70 RBX: ffff888098be2380 RCX: ffffffff81bfdf07
RDX: 1ffff1101317c47d RSI: 0000000000000001 RDI: ffff888098be23e8
RBP: 0000000000000001 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
R13: 0000000000000001 R14: 0000000000000000 R15: ffff8880854bc0b0
FS:  00007fa632ef6700(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000446a9f CR3: 000000000011b000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

Crashes (1):
Manager	Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro	VM info	Maintainers
ci-upstream-kasan-gce-root	2020/09/04 14:18	upstream	e28f0104	abf9ba4f	.config	log	report	syz	C		linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk