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References: <20211216080303.388139-1-yinxin.x@bytedance.com>
In-Reply-To: <20211216080303.388139-1-yinxin.x@bytedance.com>
From:   harshad shirwadkar <harshadshirwadkar@gmail.com>
Date:   Fri, 17 Dec 2021 12:17:24 -0800
Message-ID: <CAD+ocbzWryj6FnHR4naiBvNHN4WqyuGo_n-52J_42jpLVLeAew@mail.gmail.com>
Subject: Re: [PATCH] ext4: call fallocate may cause process to hang when using
 fast commit
To:     Xin Yin <yinxin.x@bytedance.com>
Cc:     "Theodore Y. 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 for the patch Xin, it looks good to me. I think there are a few
other places where we are not stopping the transaction before calling
commit. I'm trying to find them out.

Reviewed-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>

On Thu, Dec 16, 2021 at 12:04 AM Xin Yin <yinxin.x@bytedance.com> wrote:
>
> If open a file with O_SYNC, and call fallocate with mode=0.when using
> fast commit, will cause the process to hang.
>
> During the fast_commit procedure, it will wait for inode update done.
> call ext4_fc_stop_update() before ext4_fc_commit() to mark inode
> complete update.
>
> Signed-off-by: Xin Yin <yinxin.x@bytedance.com>
> ---
>  fs/ext4/extents.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 4108896d471b..92db33887b6c 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -4707,8 +4707,12 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
>                 goto out;
>
>         if (file->f_flags & O_SYNC && EXT4_SB(inode->i_sb)->s_journal) {
> +               ext4_fc_stop_update(inode);
>                 ret = ext4_fc_commit(EXT4_SB(inode->i_sb)->s_journal,
>                                         EXT4_I(inode)->i_sync_tid);
> +               inode_unlock(inode);
> +               trace_ext4_fallocate_exit(inode, offset, max_blocks, ret);
> +               return ret;
>         }
>  out:
>         inode_unlock(inode);
> --
> 2.20.1
>