Date:   Mon, 8 Nov 2021 23:20:45 -0800
From:   Christoph Hellwig <hch@infradead.org>
To:     syzbot <syzbot+a8e049cd3abd342936b6@syzkaller.appspotmail.com>
Cc:     djwong@kernel.org, hch@infradead.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-xfs@vger.kernel.org, syzkaller-bugs@googlegroups.com,
        linux-ext4@vger.kernel.org
Subject: Re: [syzbot] WARNING in iomap_iter
Message-ID: <YYohTeK7DviCg7Nu@infradead.org>
References: <000000000000f2075605d04f9964@google.com>
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This is:

	WARN_ON_ONCE(iter->iomap.offset > iter->pos);

so it looks like ext4 has an issue in its ->iomap_begin implementation

On Mon, Nov 08, 2021 at 03:46:27PM -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    7ddb58cb0eca Merge tag 'clk-for-linus' of git://git.kernel..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=13443b82b00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=a30ce238f371e547
> dashboard link: https://syzkaller.appspot.com/bug?extid=a8e049cd3abd342936b6
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> userspace arch: i386
> 
> 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+a8e049cd3abd342936b6@syzkaller.appspotmail.com
> 
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 1112 at fs/iomap/iter.c:33 iomap_iter_done fs/iomap/iter.c:33 [inline]
> WARNING: CPU: 0 PID: 1112 at fs/iomap/iter.c:33 iomap_iter+0xdcf/0x11b0 fs/iomap/iter.c:78
> Modules linked in:
> CPU: 0 PID: 1112 Comm: kworker/u4:5 Not tainted 5.15.0-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Workqueue: loop0 loop_rootcg_workfn
> RIP: 0010:iomap_iter_done fs/iomap/iter.c:33 [inline]
> RIP: 0010:iomap_iter+0xdcf/0x11b0 fs/iomap/iter.c:78
> Code: fd ff ff e8 93 9f d1 ff e9 f9 f9 ff ff e8 79 24 8b ff 0f 0b e9 85 f8 ff ff e8 6d 24 8b ff 0f 0b e9 96 f7 ff ff e8 61 24 8b ff <0f> 0b e9 f8 f6 ff ff e8 55 24 8b ff 0f 0b 48 b8 00 00 00 00 00 fc
> RSP: 0018:ffffc90004d4f680 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: ffffc90004d4f818 RCX: 0000000000000000
> RDX: ffff88801c181d00 RSI: ffffffff81ec9faf RDI: 0000000000000003
> RBP: ffffc90004d4f848 R08: 00000fff80000000 R09: 000000000000000c
> R10: ffffffff81ec96a0 R11: 000000000000003f R12: ffffc90004d4f820
> R13: ffffffff80000000 R14: ffffc90004d4f840 R15: ffffc90004d4f888
> FS:  0000000000000000(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fc3d2148008 CR3: 00000000307d5000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  __iomap_dio_rw+0x6b2/0x1a10 fs/iomap/direct-io.c:588
>  iomap_dio_rw+0x38/0x90 fs/iomap/direct-io.c:679
>  ext4_dio_read_iter fs/ext4/file.c:77 [inline]
>  ext4_file_read_iter+0x41c/0x5d0 fs/ext4/file.c:128
>  call_read_iter include/linux/fs.h:2155 [inline]
>  lo_rw_aio.isra.0+0xa99/0xc90 drivers/block/loop.c:453
>  do_req_filebacked drivers/block/loop.c:497 [inline]
>  loop_handle_cmd drivers/block/loop.c:1857 [inline]
>  loop_process_work+0x92f/0x1db0 drivers/block/loop.c:1897
>  process_one_work+0x9b2/0x1690 kernel/workqueue.c:2298
>  worker_thread+0x658/0x11f0 kernel/workqueue.c:2445
>  kthread+0x405/0x4f0 kernel/kthread.c:327
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
>  </TASK>
> 
> 
> ---
> This report 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 syzkaller@googlegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
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