linux-ext4 - Re: [PATCH v5 4/4] ext4: data=journal: write-protect pages on j_submit_inode_data

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Date:   Thu, 8 Oct 2020 22:10:50 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Mauricio Faria de Oliveira <mfo@...onical.com>
Cc:     linux-ext4@...r.kernel.org, ocfs2-devel@....oracle.com,
        Jan Kara <jack@...e.cz>, Andreas Dilger <adilger@...ger.ca>,
        dann frazier <dann.frazier@...onical.com>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>
Subject: Re: [PATCH v5 4/4] ext4: data=journal: write-protect pages on
 j_submit_inode_data_buffers()

On Mon, Oct 05, 2020 at 09:48:41PM -0300, Mauricio Faria de Oliveira wrote:
> This implements journal callbacks j_submit|finish_inode_data_buffers()
> with different behavior for data=journal: to write-protect pages under
> commit, preventing changes to buffers writeably mapped to userspace.
> 
> If a buffer's content changes between commit's checksum calculation
> and write-out to disk, it can cause journal recovery/mount failures
> upon a kernel crash or power loss.
> 
>     [   27.334874] EXT4-fs: Warning: mounting with data=journal disables delayed allocation, dioread_nolock, and O_DIRECT support!
>     [   27.339492] JBD2: Invalid checksum recovering data block 8705 in log
>     [   27.342716] JBD2: recovery failed
>     [   27.343316] EXT4-fs (loop0): error loading journal
>     mount: /ext4: can't read superblock on /dev/loop0.
> 
> In j_submit_inode_data_buffers() we write-protect the inode's pages
> with write_cache_pages() and redirty w/ writepage callback if needed.
> 
> In j_finish_inode_data_buffers() there is nothing do to.
> 
> And in order to use the callbacks, inodes are added to the inode list
> in transaction in __ext4_journalled_writepage() and ext4_page_mkwrite().
> 
> In ext4_page_mkwrite() we must make sure that the buffers are attached
> to the transaction as jbddirty with write_end_fn(), as already done in
> __ext4_journalled_writepage().
> 
> Signed-off-by: Mauricio Faria de Oliveira <mfo@...onical.com>
> Reported-by: Dann Frazier <dann.frazier@...onical.com>
> Reported-by: kernel test robot <lkp@...el.com> # wbc.nr_to_write
> Suggested-by: Jan Kara <jack@...e.cz>
> Reviewed-by: Jan Kara <jack@...e.cz>

Thanks, applied.

					- Ted