linux-ext4 - Re: [PATCH v2 3/3] ext4: do not update s_last

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Date:   Mon, 23 Apr 2018 16:08:00 +0200
From:   Jan Kara <jack@...e.cz>
To:     Amir Goldstein <amir73il@...il.com>
Cc:     Theodore Tso <tytso@....edu>, Jan Kara <jack@...e.cz>,
        linux-ext4@...r.kernel.org
Subject: Re: [PATCH v2 3/3] ext4: do not update s_last_mounted of a frozen fs

On Sun 22-04-18 18:10:59, Amir Goldstein wrote:
> If fs is frozen after mount and before the first file open, the
> update of s_last_mounted bypasses freeze protection and prints out
> a WARNING splat:
> 
> $ mount /vdf
> $ fsfreeze -f /vdf
> $ cat /vdf/foo
> 
> [   31.578555] WARNING: CPU: 1 PID: 1415 at
> fs/ext4/ext4_jbd2.c:53 ext4_journal_check_start+0x48/0x82
> 
> [   31.614016] Call Trace:
> [   31.614997]  __ext4_journal_start_sb+0xe4/0x1a4
> [   31.616771]  ? ext4_file_open+0xb6/0x189
> [   31.618094]  ext4_file_open+0xb6/0x189
> 
> If fs is frozen, skip s_last_mounted update.
> 
> [backport hint: to apply to stable tree, need to apply also patches
>  vfs: add the sb_start_intwrite_trylock() helper
>  ext4: factor out helper ext4_sample_last_mounted()]

Looks good to me. Just one nit:

> @@ -406,12 +406,14 @@ static int ext4_sample_last_mounted(struct super_block *sb,
>  	path.mnt = mnt;
>  	path.dentry = mnt->mnt_root;
>  	cp = d_path(&path, buf, sizeof(buf));
> +	err = 0;
>  	if (IS_ERR(cp))
> -		return 0;
> +		goto out_intwrite;
>  
>  	handle = ext4_journal_start_sb(sb, EXT4_HT_MISC, 1);
> +	err = PTR_ERR(handle);
>  	if (IS_ERR(handle))
> -		return PTR_ERR(handle);
> +		goto out_intwrite;
>  	BUFFER_TRACE(sbi->s_sbh, "get_write_access");
>  	err = ext4_journal_get_write_access(handle, sbi->s_sbh);
>  	if (err)
> @@ -421,6 +423,8 @@ static int ext4_sample_last_mounted(struct super_block *sb,
>  	ext4_handle_dirty_super(handle, sb);
>  out:
>  	ext4_journal_stop(handle);
> +out_intwrite:
> +	sb_end_intwrite(sb);
>  	return err;
>  }

Usually 'out' is the outermost label. So I'd rename 'out' to 'out_journal'
to avoid confusion in the future. With that fixed feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR