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From:   harshad shirwadkar <harshadshirwadkar@gmail.com>
Date:   Mon, 26 Oct 2020 15:28:41 -0700
Message-ID: <CAD+ocby3hA0GCm5Rf6T3UF+2UWgWoUjrz7=VzbeUMjX6Qx8D5g@mail.gmail.com>
Subject: Re: [PATCH] ext4: properly check for dirty state in ext4_inode_datasync_dirty()
To:     Andrea Righi <andrea.righi@canonical.com>
Cc:     "Theodore Ts'o" <tytso@mit.edu>,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        Ext4 Developers List <linux-ext4@vger.kernel.org>,
        linux-kernel@vger.kernel.org
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Thanks Andrea for catching and sending out a fix for this.

On Sat, Oct 24, 2020 at 7:01 AM Andrea Righi <andrea.righi@canonical.com> wrote:
>
> ext4_inode_datasync_dirty() needs to return 'true' if the inode is
> dirty, 'false' otherwise, but the logic seems to be incorrectly changed
> by commit aa75f4d3daae ("ext4: main fast-commit commit path").
>
> This introduces a problem with swap files that are always failing to be
> activated, showing this error in dmesg:
>
>  [   34.406479] swapon: file is not committed
>
> Simple test case to reproduce the problem:
>
>   # fallocate -l 8G swapfile
>   # chmod 0600 swapfile
>   # mkswap swapfile
>   # swapon swapfile
>
> Fix the logic to return the proper state of the inode.
>
> Link: https://lore.kernel.org/lkml/20201024131333.GA32124@xps-13-7390
> Fixes: aa75f4d3daae ("ext4: main fast-commit commit path")
> Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
> ---
>  fs/ext4/inode.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 03c2253005f0..a890a17ab7e1 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3308,8 +3308,8 @@ static bool ext4_inode_datasync_dirty(struct inode *inode)
>         if (journal) {
>                 if (jbd2_transaction_committed(journal,
>                                         EXT4_I(inode)->i_datasync_tid))
> -                       return true;
> -               return atomic_read(&EXT4_SB(inode->i_sb)->s_fc_subtid) >=
> +                       return false;
> +               return atomic_read(&EXT4_SB(inode->i_sb)->s_fc_subtid) <
>                         EXT4_I(inode)->i_fc_committed_subtid;
In addition, the above condition should only be checked if fast
commits are enabled. So, in effect this overall condition will look
like this:

if (journal) {
    if (jbd2_transaction_committed(journal, EXT4_I(inode)->i_datasync_tid))
        return false;
    if (test_opt2(sb, JOURNAL_FAST_COMMIT))
        return atomic_read(&EXT4_SB(inode->i_sb)->s_fc_subtid) <
EXT4_I(inode)->i_fc_committed_subtid;
    return true;
}

Thanks,
Harshad

>         }
>
> --
> 2.27.0
>