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From: Andreas Dilger <adilger@dilger.ca>
To: Jan Kara <jack@suse.cz>, Eric Biggers <ebiggers@kernel.org>
Cc: Ted Tso <tytso@mit.edu>, linux-ext4@vger.kernel.org
Subject: Re: [PATCH 02/12] ext4: Remove redundant sb checksum recomputation
Date: Sun, 29 Nov 2020 15:11:05 -0700	[thread overview]
Message-ID: <301139FC-B346-4199-B26E-1FF0CB970746@dilger.ca> (raw)
In-Reply-To: <20201127113405.26867-3-jack@suse.cz>

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On Nov 27, 2020, at 4:33 AM, Jan Kara <jack@suse.cz> wrote:
> 
> Superblock is written out either through ext4_commit_super() or through
> ext4_handle_dirty_super(). In both cases we recompute the checksum so it
> is not necessary to recompute it after updating superblock free inodes &
> blocks counters.

I searched through the code to see where s_sbh is being used, and it
looks like there is one case that doesn't update the checksum using
ext4_handle_dirty_super(), namely:

ext4_file_ioctl(cmd=FS_IOC_GET_ENCRYPTION_PWSALT)
{
                        err = ext4_journal_get_write_access(handle, sbi->s_sbh);
                        if (err)
                                goto pwsalt_err_journal;
                        generate_random_uuid(sbi->s_es->s_encrypt_pw_salt);
                        err = ext4_handle_dirty_metadata(handle, NULL,
                                                         sbi->s_sbh);

I don't think that is a problem with this patch, per se, but looks like
a bug that could be hit in rare cases with fscrypt + metadata_csum.  It
would only happen once per filesystem, and would normally be hidden by
later superblock updates, but should probably be fixed anyway.

Reviewed-by: Andreas Dilger <adilger@dilger.ca>

> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
> fs/ext4/super.c | 2 --
> 1 file changed, 2 deletions(-)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 2b08b162075c..61e6e5f156f3 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -5004,13 +5004,11 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> 	block = ext4_count_free_clusters(sb);
> 	ext4_free_blocks_count_set(sbi->s_es,
> 				   EXT4_C2B(sbi, block));
> -	ext4_superblock_csum_set(sb);
> 	err = percpu_counter_init(&sbi->s_freeclusters_counter, block,
> 				  GFP_KERNEL);
> 	if (!err) {
> 		unsigned long freei = ext4_count_free_inodes(sb);
> 		sbi->s_es->s_free_inodes_count = cpu_to_le32(freei);
> -		ext4_superblock_csum_set(sb);
> 		err = percpu_counter_init(&sbi->s_freeinodes_counter, freei,
> 					  GFP_KERNEL);
> 	}
> --
> 2.16.4
> 


Cheers, Andreas






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  reply	other threads:[~2020-11-29 22:12 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-27 11:33 [PATCH 00/12] ext4: Various fixes of ext4 handling of fs errors Jan Kara
2020-11-27 11:33 ` [PATCH 01/12] ext4: Don't remount read-only with errors=continue on reboot Jan Kara
2020-11-29 21:33   ` Andreas Dilger
2020-12-16  4:59     ` Theodore Y. Ts'o
2020-11-27 11:33 ` [PATCH 02/12] ext4: Remove redundant sb checksum recomputation Jan Kara
2020-11-29 22:11   ` Andreas Dilger [this message]
2020-11-30 10:59     ` Jan Kara
2020-12-16  5:01   ` Theodore Y. Ts'o
2020-11-27 11:33 ` [PATCH 03/12] ext4: Standardize error message in ext4_protect_reserved_inode() Jan Kara
2020-11-29 21:39   ` Andreas Dilger
2020-12-16  5:04   ` Theodore Y. Ts'o
2020-11-27 11:33 ` [PATCH 04/12] ext4: Make ext4_abort() use __ext4_error() Jan Kara
2020-11-29 22:12   ` Andreas Dilger
2020-12-16  5:07   ` Theodore Y. Ts'o
2020-11-27 11:33 ` [PATCH 05/12] ext4: Move functions in super.c Jan Kara
2020-11-29 22:13   ` Andreas Dilger
2020-12-16  5:09   ` Theodore Y. Ts'o
2020-11-27 11:33 ` [PATCH 06/12] ext4: Simplify ext4 error translation Jan Kara
2020-11-29 21:57   ` Andreas Dilger
2020-12-16  5:11   ` Theodore Y. Ts'o
2020-11-27 11:34 ` [PATCH 07/12] ext4: Defer saving error info from atomic context Jan Kara
2020-12-16  5:31   ` Theodore Y. Ts'o
2020-12-16  5:40     ` Theodore Y. Ts'o
2020-12-16  9:56       ` Jan Kara
2020-11-27 11:34 ` [PATCH 08/12] ext4: Combine ext4_handle_error() and save_error_info() Jan Kara
2020-12-14 19:23   ` harshad shirwadkar
2020-12-16 10:11     ` Jan Kara
2020-12-16 10:24       ` Jan Kara
2020-11-27 11:34 ` [PATCH 09/12] ext4: Drop sync argument of ext4_commit_super() Jan Kara
2020-12-14 19:25   ` harshad shirwadkar
2020-11-27 11:34 ` [PATCH 10/12] ext4: Protect superblock modifications with a buffer lock Jan Kara
2020-11-27 11:34 ` [PATCH 11/12] ext4: Save error info to sb through journal if available Jan Kara
2020-11-27 11:34 ` [PATCH 12/12] ext4: Use sbi instead of EXT4_SB(sb) in ext4_update_super() Jan Kara
2020-12-14 19:07 ` [PATCH 00/12] ext4: Various fixes of ext4 handling of fs errors harshad shirwadkar

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