Subject: Re: WARNING in ext4_da_update_reserve_space

From: Murilo Opsfelder Araújo <[email-masked]>
Date: Thu, 02 Apr 2020 11:06:10 -0300

On Thursday, April 2, 2020 8:02:11 AM -03 syzbot wrote:
> 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 <[email-masked]>
> Date:   Wed Aug 1 21:33:15 2018 +0000
>
>     powerpc/traps: Print unhandled signals in a separate function

This commit is specific to powerpc and the crash is from an x86_64 system.

There is a bunch of scp errors in the logs:

scp: ./syz-executor998635077: No space left on device

Is it possible that these errors might be misleading the syzbot?

>
> 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: [email-masked]
> 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..
>
>
> ---
> 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 [email-masked].
>
> syzbot will keep track of this bug report. See:
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> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this bug, for details see:
> https://goo.gl/tpsmEJ#testing-patches

--
Murilo