WARNING in ext4_da_update_reserve_space

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    1a147b74 Merge branch 'DSA-mtu'
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=14237713e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=46ee14d4915944bc
dashboard link: https://syzkaller.appspot.com/bug?extid=67e4f16db666b1c8253c
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12237713e00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10ec7c97e00000

The bug was bisected to:

commit 658b0f92bc7003bc734471f61bf7cd56339eb8c3
Author: Murilo Opsfelder Araujo <muriloo@xxxxxxxxxxxxx>
Date:   Wed Aug 1 21:33:15 2018 +0000

    powerpc/traps: Print unhandled signals in a separate function

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=15979f5be00000
final crash:    https://syzkaller.appspot.com/x/report.txt?x=17979f5be00000
console output: https://syzkaller.appspot.com/x/log.txt?x=13979f5be00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+67e4f16db666b1c8253c@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 658b0f92bc70 ("powerpc/traps: Print unhandled signals in a separate function")

EXT4-fs warning (device sda1): ext4_da_update_reserve_space:344: ext4_da_update_reserve_space: ino 15722, used 1 with only 0 reserved data blocks
------------[ cut here ]------------
WARNING: CPU: 1 PID: 359 at fs/ext4/inode.c:348 ext4_da_update_reserve_space+0x622/0x7d0 fs/ext4/inode.c:344
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 359 Comm: kworker/u4:5 Not tainted 5.6.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn (flush-8:0)
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x188/0x20d lib/dump_stack.c:118
 panic+0x2e3/0x75c kernel/panic.c:221
 __warn.cold+0x2f/0x35 kernel/panic.c:582
 report_bug+0x27b/0x2f0 lib/bug.c:195
 fixup_bug arch/x86/kernel/traps.c:174 [inline]
 fixup_bug arch/x86/kernel/traps.c:169 [inline]
 do_error_trap+0x12b/0x220 arch/x86/kernel/traps.c:267
 do_invalid_op+0x32/0x40 arch/x86/kernel/traps.c:286
 invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1027
RIP: 0010:ext4_da_update_reserve_space+0x622/0x7d0 fs/ext4/inode.c:348
Code: 02 00 0f 85 94 01 00 00 48 8b 7d 28 49 c7 c0 20 72 3c 88 41 56 48 c7 c1 80 60 3c 88 53 ba 58 01 00 00 4c 89 c6 e8 1e 6d 0d 00 <0f> 0b 48 b8 00 00 00 00 00 fc ff df 4c 89 ea 48 c1 ea 03 0f b6 04
RSP: 0018:ffffc90002197288 EFLAGS: 00010296
RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff820bf066 RDI: fffff52000432e21
RBP: ffff888086b744c8 R08: 0000000000000091 R09: ffffed1015ce6659
R10: ffffed1015ce6658 R11: ffff8880ae7332c7 R12: 0000000000000001
R13: ffff888086b74990 R14: 0000000000000000 R15: ffff888086b74a40
 ext4_ext_map_blocks+0x24aa/0x37d0 fs/ext4/extents.c:4500
 ext4_map_blocks+0x4cb/0x1650 fs/ext4/inode.c:622
 mpage_map_one_extent fs/ext4/inode.c:2365 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2418 [inline]
 ext4_writepages+0x19eb/0x3080 fs/ext4/inode.c:2772
 do_writepages+0xfa/0x2a0 mm/page-writeback.c:2344
 __writeback_single_inode+0x12a/0x1410 fs/fs-writeback.c:1452
 writeback_sb_inodes+0x515/0xdd0 fs/fs-writeback.c:1716
 wb_writeback+0x2a5/0xd90 fs/fs-writeback.c:1892
 wb_do_writeback fs/fs-writeback.c:2037 [inline]
 wb_workfn+0x339/0x11c0 fs/fs-writeback.c:2078
 process_one_work+0x94b/0x1690 kernel/workqueue.c:2266
 worker_thread+0x96/0xe20 kernel/workqueue.c:2412
 kthread+0x357/0x430 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
Kernel Offset: disabled
Rebooting in 86400 seconds..


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