linux-kernel - Re: [syzbot] divide error in wb_update_dirty

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Message-Id: <20210802133106.7106b66013665ead219a1d15@linux-foundation.org>
Date:   Mon, 2 Aug 2021 13:31:06 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     syzbot <syzbot+6a04d6ba849df9d81239@...kaller.appspotmail.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        syzkaller-bugs@...glegroups.com, Jan Kara <jack@...e.cz>
Subject: Re: [syzbot] divide error in wb_update_dirty_ratelimit

On Mon, 02 Aug 2021 11:24:20 -0700 syzbot <syzbot+6a04d6ba849df9d81239@...kaller.appspotmail.com> wrote:

> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    8d4b477da1a8 Add linux-next specific files for 20210730
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=128ede56300000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=4adf4987f875c210
> dashboard link: https://syzkaller.appspot.com/bug?extid=6a04d6ba849df9d81239
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+6a04d6ba849df9d81239@...kaller.appspotmail.com
> 
> divide error: 0000 [#1] PREEMPT SMP KASAN
> CPU: 0 PID: 10430 Comm: syz-executor.3 Not tainted 5.14.0-rc3-next-20210730-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> RIP: 0010:wb_update_dirty_ratelimit+0x18d/0x7d0 mm/page-writeback.c:1197

Thanks.

Presumably wb_update_dirty_ratelimit() was passed elapsed==0.  Jan,
could your changes have caused this?

> Code: 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 af 05 00 00 4c 2b b5 30 02 00 00 49 8d 7f 58 31 d2 49 6b c6 64 <48> f7 f3 48 89 fa 48 89 04 24 48 b8 00 00 00 00 00 fc ff df 48 c1
> RSP: 0018:ffffc9000551f750 EFLAGS: 00010206
> RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffc9000fdb1000
> RDX: 0000000000000000 RSI: 0000000000006377 RDI: ffffc9000551f9a0
> RBP: ffff888089632060 R08: 0000000000000000 R09: ffffffff9023d363
> R10: fffffbfff2047a6c R11: 0000000000000000 R12: 0000000000006400
> R13: 000000000003c2b1 R14: 0000000000000000 R15: ffffc9000551f948
> FS:  00007fdc4e708700(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000206000bf CR3: 0000000073f41000 CR4: 00000000001506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  __wb_update_bandwidth+0x3d7/0x5a0 mm/page-writeback.c:1350
>  balance_dirty_pages+0x12ab/0x29d0 mm/page-writeback.c:1719
>  balance_dirty_pages_ratelimited+0xda2/0x1820 mm/page-writeback.c:1920
>  generic_perform_write+0x320/0x510 mm/filemap.c:3789
>  __generic_file_write_iter+0x24e/0x610 mm/filemap.c:3882
>  generic_file_write_iter+0xd7/0x220 mm/filemap.c:3914
>  fuse_cache_write_iter fs/fuse/file.c:1298 [inline]
>  fuse_file_write_iter+0x56c/0xcd0 fs/fuse/file.c:1601
>  call_write_iter include/linux/fs.h:2152 [inline]
>  new_sync_write+0x426/0x650 fs/read_write.c:518
>  vfs_write+0x75a/0xa40 fs/read_write.c:605
>  ksys_write+0x12d/0x250 fs/read_write.c:658
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> RIP: 0033:0x4665e9
> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007fdc4e708188 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> RAX: ffffffffffffffda RBX: 000000000056bf80 RCX: 00000000004665e9
> RDX: 00000000fffffdef RSI: 00000000200000c0 RDI: 0000000000000006
> RBP: 00000000004bfcc4 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 000000000056bf80
> R13: 00007fff2d6f27cf R14: 00007fdc4e708300 R15: 0000000000022000
> Modules linked in:
> ---[ end trace 01891e5696647ce8 ]---
> RIP: 0010:wb_update_dirty_ratelimit+0x18d/0x7d0 mm/page-writeback.c:1197
> Code: 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 af 05 00 00 4c 2b b5 30 02 00 00 49 8d 7f 58 31 d2 49 6b c6 64 <48> f7 f3 48 89 fa 48 89 04 24 48 b8 00 00 00 00 00 fc ff df 48 c1
> RSP: 0018:ffffc9000551f750 EFLAGS: 00010206
> RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffc9000fdb1000
> RDX: 0000000000000000 RSI: 0000000000006377 RDI: ffffc9000551f9a0
> RBP: ffff888089632060 R08: 0000000000000000 R09: ffffffff9023d363
> R10: fffffbfff2047a6c R11: 0000000000000000 R12: 0000000000006400
> R13: 000000000003c2b1 R14: 0000000000000000 R15: ffffc9000551f948
> FS:  00007fdc4e708700(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000206000bf CR3: 0000000073f41000 CR4: 00000000001506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400