linux-ext4 - Re: [PATCH] ext4: don't track ranges in fast

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Message-ID: <87r0ctbbyc.fsf@brahms.olymp>
Date: Wed, 19 Jun 2024 08:58:51 +0100
From: Luis Henriques <luis.henriques@...ux.dev>
To: Ben Hutchings <ben@...adent.org.uk>
Cc: Theodore Ts'o <tytso@....edu>,  Andreas Dilger <adilger@...ger.ca>,
  Harshad Shirwadkar <harshadshirwadkar@...il.com>,
  linux-ext4@...r.kernel.org,  1039883@...s.debian.org
Subject: Re: [PATCH] ext4: don't track ranges in fast_commit if inode has
 inlined data

On Wed 19 Jun 2024 12:30:38 AM +02, Ben Hutchings wrote;

> On Tue, 2024-06-18 at 15:43 +0100, Luis Henriques (SUSE) wrote:
>> When fast-commit needs to track ranges, it has to handle inodes that have
>> inlined data in a different way because ext4_fc_write_inode_data(), in the
>> actual commit path, will attempt to map the required blocks for the range.
>> However, inodes that have inlined data will have it's data stored in
>> inode->i_block and, eventually, in the extended attribute space.
>> 
>> Unfortunately, because fast commit doesn't currently support extended
>> attributes, the solution is to mark this commit as ineligible.
>> 
>> Link: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1039883
>> Signed-off-by: Luis Henriques (SUSE) <luis.henriques@...ux.dev>
>
> Reported-by: Hervé Werner <dud225@...mail.com>
> Tested-by: Ben Hutchings <benh@...ian.org>
>

Thanks a lot, Ben.

> I think this should also have:
>
> Fixes: 9725958bb75c ("ext4: fast commit may miss tracking unwritten range during ftruncate")
>
> unless you think the problem is even older than that.

If my understanding is correct (hopefully someone will confirm that!), I
think the problem goes further back.  That commit just makes it more
likely to be visible, but handling of inlined data is incorrect since the
fast_commit merge.  So, I guess that's better to simply add:

Cc: stable@...r.kernel.org

Cheers,
-- 
Luís


>
> Ben.
>
>> ---
>>  fs/ext4/fast_commit.c | 6 ++++++
>>  1 file changed, 6 insertions(+)
>> 
>> diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
>> index 87c009e0c59a..d3a67bc06d10 100644
>> --- a/fs/ext4/fast_commit.c
>> +++ b/fs/ext4/fast_commit.c
>> @@ -649,6 +649,12 @@ void ext4_fc_track_range(handle_t *handle, struct inode *inode, ext4_lblk_t star
>>  	if (ext4_test_mount_flag(inode->i_sb, EXT4_MF_FC_INELIGIBLE))
>>  		return;
>>  
>> +	if (ext4_has_inline_data(inode)) {
>> +		ext4_fc_mark_ineligible(inode->i_sb, EXT4_FC_REASON_XATTR,
>> +					handle);
>> +		return;
>> +	}
>> +
>>  	args.start = start;
>>  	args.end = end;
>>  
>
> -- 
> Ben Hutchings
> For every complex problem
> there is a solution that is simple, neat, and wrong.
>