BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 96ec0067 P4D 96ec0067 PUD 96ec1067 PMD 0 
Oops: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 8498 Comm: syz-executor.5 Not tainted 5.7.0-rc7-next-20200529-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:__sanitizer_cov_trace_pc+0x43/0x60 kernel/kcov.c:202
Code: 24 74 0f 80 e6 01 74 35 8b 90 0c 14 00 00 85 d2 74 2b 8b 90 e8 13 00 00 83 fa 02 75 20 48 8b 88 f0 13 00 00 8b 80 ec 13 00 00 <48> 8b 11 48 83 c2 01 48 39 d0 76 07 48 89 34 d1 48 89 11 c3 66 0f
RSP: 0018:ffffc90002a87948 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000015000 RCX: 0000000000000000
RDX: 0000000000000002 RSI: ffffffff8191b944 RDI: 0000000000000007
RBP: ffffea0001a0c980 R08: ffff88808ff285c0 R09: fffff94000341931
R10: ffffea0001a0c987 R11: fffff94000341930 R12: 0000000000000000
R13: dead000000000100 R14: 0000000000000001 R15: ffffea0001a0c988
FS:  00007ffa2becb700(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000009719b000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 compound_head include/linux/page-flags.h:182 [inline]
 PageLocked include/linux/page-flags.h:320 [inline]
 unlock_page+0x54/0x2a0 mm/filemap.c:1307
 generic_write_end+0x107/0x3d0 fs/buffer.c:2228
 ext4_da_write_end+0x211/0xbe0 fs/ext4/inode.c:3096
 generic_perform_write+0x2c0/0x4e0 mm/filemap.c:3348
 ext4_buffered_write_iter+0x1f7/0x450 fs/ext4/file.c:270
 ext4_file_write_iter+0x1ec/0x13f0 fs/ext4/file.c:649
 call_write_iter include/linux/fs.h:1926 [inline]
 new_sync_write+0x426/0x650 fs/read_write.c:484
 __vfs_write+0xc9/0x100 fs/read_write.c:497
 vfs_write+0x268/0x5d0 fs/read_write.c:559
 ksys_write+0x12d/0x250 fs/read_write.c:612
 do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:359
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45ca59
Code: 0d 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 db b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffa2becac78 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 000000000050d560 RCX: 000000000045ca59
RDX: 0000000000400086 RSI: 0000000020000200 RDI: 0000000000000003
RBP: 000000000078bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000d0e R14: 00000000004cf64a R15: 00007ffa2becb6d4
Modules linked in:
CR2: 0000000000000000
---[ end trace e86061d728418190 ]---
RIP: 0010:__sanitizer_cov_trace_pc+0x43/0x60 kernel/kcov.c:202
Code: 24 74 0f 80 e6 01 74 35 8b 90 0c 14 00 00 85 d2 74 2b 8b 90 e8 13 00 00 83 fa 02 75 20 48 8b 88 f0 13 00 00 8b 80 ec 13 00 00 <48> 8b 11 48 83 c2 01 48 39 d0 76 07 48 89 34 d1 48 89 11 c3 66 0f
RSP: 0018:ffffc90002a87948 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000015000 RCX: 0000000000000000
RDX: 0000000000000002 RSI: ffffffff8191b944 RDI: 0000000000000007
RBP: ffffea0001a0c980 R08: ffff88808ff285c0 R09: fffff94000341931
R10: ffffea0001a0c987 R11: fffff94000341930 R12: 0000000000000000
R13: dead000000000100 R14: 0000000000000001 R15: ffffea0001a0c988
FS:  00007ffa2becb700(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b3052d000 CR3: 000000009719b000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400