linux-kernel - Re: [syzbot] [btrfs?] WARNING in btrfs_use_block

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Date:   Tue, 28 Nov 2023 17:40:10 +0100
From:   David Sterba <dsterba@...e.cz>
To:     Anand Jain <anand.jain@...cle.com>
Cc:     syzbot <syzbot+10d5b62a8d7046b86d22@...kaller.appspotmail.com>,
        clm@...com, dsterba@...e.com, josef@...icpanda.com,
        linux-btrfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [btrfs?] WARNING in btrfs_use_block_rsv

On Sun, Nov 26, 2023 at 06:59:41AM +0800, Anand Jain wrote:
> 
> 
> On 25/11/2023 10:08, syzbot wrote:
> > syzbot has bisected this issue to:
> > 
> > commit a5b8a5f9f8355d27a4f8d0afa93427f16d2f3c1e
> > Author: Anand Jain <anand.jain@...cle.com>
> > Date:   Thu Sep 28 01:09:47 2023 +0000
> > 
> >      btrfs: support cloned-device mount capability
> > 
> > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1446d344e80000
> > start commit:   d3fa86b1a7b4 Merge tag 'net-6.7-rc3' of git://git.kernel.o..
> > git tree:       upstream
> > final oops:     https://syzkaller.appspot.com/x/report.txt?x=1646d344e80000
> > console output: https://syzkaller.appspot.com/x/log.txt?x=1246d344e80000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=6ae1a4ee971a7305
> > dashboard link: https://syzkaller.appspot.com/bug?extid=10d5b62a8d7046b86d22
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1431040ce80000
> > 
> > Reported-by: syzbot+10d5b62a8d7046b86d22@...kaller.appspotmail.com
> > Fixes: a5b8a5f9f835 ("btrfs: support cloned-device mount capability")
> > 
> > For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> 
> 
> It is completely strange that this issue bisects to the commit
> a5b8a5f9f835 ('btrfs: support cloned-device mount capability').
> I am unable to reproduce this as well.

I think it's because of changed timing or it can be an inconclusive
bisect. Things around space handling depend on timing, the test would
need to be run a few times to be sure.

The report provides an image so it may be good to analyze if it's scaled
properly or if the reproducer does something strange.

> -------------------
> WARNING: CPU: 1 PID: 58 at fs/btrfs/block-rsv.c:523 
> btrfs_use_block_rsv+0x60d/0x860 fs/btrfs/block-rsv.c:523
> <snap>
> Call Trace:
>   <TASK>
>   btrfs_alloc_tree_block+0x1e0/0x12c0 fs/btrfs/extent-tree.c:5114
>   btrfs_force_cow_block+0x3e5/0x19e0 fs/btrfs/ctree.c:563
>   btrfs_cow_block+0x2b6/0xb30 fs/btrfs/ctree.c:741
>   push_leaf_left+0x315/0x4d0 fs/btrfs/ctree.c:3485
>   split_leaf+0x9c3/0x13b0 fs/btrfs/ctree.c:3681
>   search_leaf fs/btrfs/ctree.c:1944 [inline]
>   btrfs_search_slot+0x24ba/0x2fd0 fs/btrfs/ctree.c:2131
>   btrfs_insert_empty_items+0xb6/0x1b0 fs/btrfs/ctree.c:4285
>   btrfs_insert_empty_item fs/btrfs/ctree.h:657 [inline]
>   insert_reserved_file_extent+0x7aa/0x950 fs/btrfs/inode.c:2907
>   insert_ordered_extent_file_extent fs/btrfs/inode.c:3005 [inline]
>   btrfs_finish_one_ordered+0x12dc/0x20d0 fs/btrfs/inode.c:3113
>   btrfs_work_helper+0x210/0xbf0 fs/btrfs/async-thread.c:315
>   process_one_work+0x886/0x15d0 kernel/workqueue.c:2630
>   process_scheduled_works kernel/workqueue.c:2703 [inline]
>   worker_thread+0x8b9/0x1290 kernel/workqueue.c:2784
>   kthread+0x2c6/0x3a0 kernel/kthread.c:388
>   ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
>   ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
> -----------------
> 
> btrfs_use_block_rsv()
> <snap>
>          /*
>           * The global reserve still exists to save us from ourselves, 
> so don't
>           * warn_on if we are short on our delayed refs reserve.
>           */
>          if (block_rsv->type != BTRFS_BLOCK_RSV_DELREFS &&
>              btrfs_test_opt(fs_info, ENOSPC_DEBUG)) {
>                  static DEFINE_RATELIMIT_STATE(_rs,
>                                  DEFAULT_RATELIMIT_INTERVAL * 10,
>                                  /*DEFAULT_RATELIMIT_BURST*/ 1);
>                  if (__ratelimit(&_rs))
>                          WARN(1, KERN_DEBUG
>                                  "BTRFS: block rsv %d returned %d\n",
>                                  block_rsv->type, ret);
>          }
> ----------