linux-ext4 - Re: [PATCH v3 2/4] jbd2: discard dirty data when forgetting an un-journalled buffer

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Message-ID: <20190128152616.GF5858@quack2.suse.cz>
Date:   Mon, 28 Jan 2019 16:26:16 +0100
From:   Jan Kara <jack@...e.cz>
To:     "zhangyi (F)" <yi.zhang@...wei.com>
Cc:     linux-ext4@...r.kernel.org, tytso@....edu, jack@...e.cz,
        adilger.kernel@...ger.ca, miaoxie@...wei.com
Subject: Re: [PATCH v3 2/4] jbd2: discard dirty data when forgetting an
 un-journalled buffer

On Fri 25-01-19 20:30:54, zhangyi (F) wrote:
> We do not unmap and clear dirty flag when forgetting a buffer without
> journal or does not belongs to any transaction, so the invalid dirty
> data may still be written to the disk later. It's fine if the
> corresponding block is never used before the next mount, and it's also
> fine that we invoke clean_bdev_aliases() related functions to unmap
> the block device mapping when re-allocating such freed block as data
> block. But this logic is somewhat fragile and risky that may lead to
> data corruption if we forget to clean bdev aliases. So, It's better to
> discard dirty data during forget time.
> 
> We have been already handled all the cases of forgetting journalled
> buffer, this patch deal with the remaining two cases.
> 
> - buffer is not journalled yet,
> - buffer is journalled but doesn't belongs to any transaction.
> 
> We invoke __bforget() instead of __brelese() when forgetting an
> un-journalled buffer in jbd2_journal_forget(). After this patch we can
> remove all clean_bdev_aliases() related calls in ext4.
> 
> Suggested-by: Jan Kara <jack@...e.cz>
> Signed-off-by: zhangyi (F) <yi.zhang@...wei.com>

Thanks for the patch! Just one small comment below:

> +		/*
> +		 * The buffer is still not written to disk, we should
> +		 * attach this buffer to current transaction to prevent
> +		 * missing writing back when doing checkpoint before
> +		 * the current transaction complete submittion.
> +		 */
> +		__jbd2_journal_temp_unlink_buffer(jh);

Calling __jbd2_journal_temp_unlink_buffer() is not needed when you know the
buffer does not belong to any transaction. Otherwise the patch looks good
to me so feel free to add:

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

after fixing this.

								Honza

> +		clear_buffer_dirty(bh);
> +		__jbd2_journal_file_buffer(jh, transaction, BJ_Forget);
> +		spin_unlock(&journal->j_list_lock);
>  	}
>  
> -not_jbd:
>  	jbd_unlock_bh_state(bh);
>  	__brelse(bh);
>  drop:
> @@ -1643,6 +1673,11 @@ int jbd2_journal_forget (handle_t *handle, struct buffer_head *bh)
>  		handle->h_buffer_credits++;
>  	}
>  	return err;
> +
> +not_jbd:
> +	jbd_unlock_bh_state(bh);
> +	__bforget(bh);
> +	goto drop;
>  }
>  
>  /**
> -- 
> 2.7.4
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR