bisecting fixing commit since 14cfdbd39e316efd91ae6e403ef8211f0b022603
building syzkaller on 78267cec1aaa5e066d66e6a6c76fea1753e51b46
testing commit 14cfdbd39e316efd91ae6e403ef8211f0b022603 with gcc (GCC) 8.1.0
kernel signature: f221a2196d50aba5bd1751d10a827daee6c6da505600666d921a1a550c89967e
all runs: crashed: BUG: unable to handle kernel NULL pointer dereference in generic_perform_write
testing current HEAD 8e2406c851877516f12b7ab4e975d033a6d58ebb
testing commit 8e2406c851877516f12b7ab4e975d033a6d58ebb with gcc (GCC) 8.1.0
kernel signature: 2d8e750859945c82b7baf70032e2b4a080bbac943043e4055c39c7e95a492789
all runs: crashed: BUG: unable to handle kernel NULL pointer dereference in generic_perform_write
revisions tested: 2, total time: 27m6.37741752s (build: 18m16.957188993s, test: 8m9.694931973s)
the crash still happens on HEAD
commit msg: Linux 4.19.117
crash: BUG: unable to handle kernel NULL pointer dereference in generic_perform_write
EXT4-fs (sda1): DAX enabled. Warning: EXPERIMENTAL, use at your own risk
EXT4-fs (sda1): warning: refusing change of dax flag with busy inodes while remounting
EXT4-fs (sda1): re-mounted. Opts: dax,
BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
PGD 925ea067 P4D 925ea067 PUD 99e57067 PMD 0 
Oops: 0010 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 10634 Comm: syz-executor.2 Not tainted 4.19.117-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:          (null)
Code: Bad RIP value.
RSP: 0018:ffff88806f7179c8 EFLAGS: 00010246
RAX: ffffffff8738cc60 RBX: 0000000000000001 RCX: 0000000000000001
RDX: 0000000000000000 RSI: ffff8880730a1578 RDI: ffff8880a9360040
RBP: ffff88806f717b00 R08: 0000000000000000 R09: ffff88806f717a58
R10: ffffed1015d64732 R11: ffff8880aeb23993 R12: 0000000000000000
R13: ffff88806f717ad8 R14: ffff8880730a1578 R15: ffff88809b792500
FS:  00007f36cd3e9700(0000) GS:ffff8880aeb00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 0000000089056000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 generic_perform_write+0x289/0x480 mm/filemap.c:3162
 __generic_file_write_iter+0x201/0x580 mm/filemap.c:3287
 ext4_file_write_iter+0x282/0xe60 fs/ext4/file.c:272
 call_write_iter include/linux/fs.h:1821 [inline]
 new_sync_write fs/read_write.c:474 [inline]
 __vfs_write+0x443/0x890 fs/read_write.c:487
 vfs_write+0x150/0x4d0 fs/read_write.c:549
 ksys_write+0x103/0x260 fs/read_write.c:599
 __do_sys_write fs/read_write.c:611 [inline]
 __se_sys_write fs/read_write.c:608 [inline]
 __x64_sys_write+0x6e/0xb0 fs/read_write.c:608
 do_syscall_64+0xd0/0x4e0 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45c849
Code: ad b6 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 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f36cd3e8c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f36cd3e96d4 RCX: 000000000045c849
RDX: 0000000000000001 RSI: 0000000020000080 RDI: 0000000000000003
RBP: 000000000076bfa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000cdc R14: 00000000004cf01a R15: 000000000076bfac
Modules linked in:
CR2: 0000000000000000
---[ end trace 21a0aaada12fc817 ]---
RIP: 0010:          (null)
Code: Bad RIP value.
RSP: 0018:ffff88806f7179c8 EFLAGS: 00010246
RAX: ffffffff8738cc60 RBX: 0000000000000001 RCX: 0000000000000001
RDX: 0000000000000000 RSI: ffff8880730a1578 RDI: ffff8880a9360040
RBP: ffff88806f717b00 R08: 0000000000000000 R09: ffff88806f717a58
R10: ffffed1015d64732 R11: ffff8880aeb23993 R12: 0000000000000000
R13: ffff88806f717ad8 R14: ffff8880730a1578 R15: ffff88809b792500
FS:  00007f36cd3e9700(0000) GS:ffff8880aeb00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 0000000089056000 CR4: 00000000001406e0
BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
PGD 8fba1067 P4D 8fba1067 PUD a8e97067 PMD 0 
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Oops: 0010 [#2] PREEMPT SMP KASAN