BUG: unable to handle kernel NULL pointer dereference in generic_perform_write

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 6525771f Merge tag 'arc-5.3-rc7' of git://git.kernel.org/p..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=164c4d12600000
kernel config: https://syzkaller.appspot.com/x/.config?x=2a6a2b9826fdadf9
dashboard link: https://syzkaller.appspot.com/bug?extid=40d67544bcae7c5347e7
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
CC: [ak...@linux-foundation.org amir...@gmail.com
darric...@oracle.com dchi...@redhat.com han...@cmpxchg.org
jo...@toxicpanda.com linux-...@vger.kernel.org linu...@kvack.org
wi...@infradead.org]

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+40d675...@syzkaller.appspotmail.com

BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor instruction fetch in kernel mode
#PF: error_code(0x0010) - not-present page
PGD 89c5c067 P4D 89c5c067 PUD 9431a067 PMD 0
Oops: 0010 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 21337 Comm: syz-executor.1 Not tainted 5.3.0-rc6+ #121
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:0x0
Code: Bad RIP value.
RSP: 0018:ffff8880a39cf9b0 EFLAGS: 00010246
RAX: ffffffff879c54c0 RBX: 0000000000000000 RCX: 0000000000000028
RDX: 0000000000000000 RSI: ffff8880876744b0 RDI: ffff88808b1c4080
RBP: ffff8880a39cfad0 R08: 0000000000000000 R09: ffff8880a39cfa48
R10: ffffed1009e52070 R11: ffff88804f290387 R12: 0000000000000028
R13: ffff8880a39cfaa8 R14: ffff8880876744b0 R15: ffff8880a39cfcc0
FS: 00007f11d5649700(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 000000004b960000 CR4: 00000000001426e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
generic_perform_write+0x23b/0x540 mm/filemap.c:3327
__generic_file_write_iter+0x25e/0x630 mm/filemap.c:3456
ext4_file_write_iter+0x373/0x1430 fs/ext4/file.c:270
call_write_iter include/linux/fs.h:1870 [inline]
new_sync_write+0x4d3/0x770 fs/read_write.c:483
__vfs_write+0xe1/0x110 fs/read_write.c:496
vfs_write+0x268/0x5d0 fs/read_write.c:558
ksys_write+0x14f/0x290 fs/read_write.c:611
__do_sys_write fs/read_write.c:623 [inline]
__se_sys_write fs/read_write.c:620 [inline]
__x64_sys_write+0x73/0xb0 fs/read_write.c:620
do_syscall_64+0xfd/0x6a0 arch/x86/entry/common.c:296
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x459879
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:00007f11d5648c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000459879
RDX: 0000000000000028 RSI: 00000000200000c0 RDI: 0000000000000003
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f11d56496d4
R13: 00000000004c93aa R14: 00000000004e0708 R15: 00000000ffffffff
Modules linked in:
CR2: 0000000000000000
---[ end trace e3d97060b907ff30 ]---
RIP: 0010:0x0
Code: Bad RIP value.
RSP: 0018:ffff8880a39cf9b0 EFLAGS: 00010246
RAX: ffffffff879c54c0 RBX: 0000000000000000 RCX: 0000000000000028
RDX: 0000000000000000 RSI: ffff8880876744b0 RDI: ffff88808b1c4080
RBP: ffff8880a39cfad0 R08: 0000000000000000 R09: ffff8880a39cfa48
R10: ffffed1009e52070 R11: ffff88804f290387 R12: 0000000000000028
R13: ffff8880a39cfaa8 R14: ffff8880876744b0 R15: ffff8880a39cfcc0
FS: 00007f11d5649700(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000738000 CR3: 000000004b960000 CR4: 00000000001426e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.