linux-ext4 - Re: [PATCH 1/4] ext4: fix incorrect tid assumption in ext4_wait_for_tail_page

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Message-ID: <874j8elxov.fsf@linux.dev>
Date: Wed, 24 Jul 2024 14:35:44 +0100
From: Luis Henriques <luis.henriques@...ux.dev>
To: Jan Kara <jack@...e.cz>
Cc: Theodore Ts'o <tytso@....edu>,  Andreas Dilger <adilger@...ger.ca>,
  Harshad Shirwadkar <harshadshirwadkar@...il.com>,
  linux-ext4@...r.kernel.org,  linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] ext4: fix incorrect tid assumption in
 ext4_wait_for_tail_page_commit()

On Wed, Jul 24 2024, Jan Kara wrote:

> On Tue 23-07-24 16:43:59, Luis Henriques (SUSE) wrote:
>> Function ext4_wait_for_tail_page_commit() assumes that '0' is not a valid
>> value for transaction IDs, which is incorrect.  Don't assume that and invoke
>> jbd2_log_wait_commit() if the journal had a committing transaction instead.
>> 
>> Signed-off-by: Luis Henriques (SUSE) <luis.henriques@...ux.dev>
>> ---
>>  fs/ext4/inode.c | 10 ++++++----
>>  1 file changed, 6 insertions(+), 4 deletions(-)
>> 
>> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
>> index 941c1c0d5c6e..e65fc2086701 100644
>> --- a/fs/ext4/inode.c
>> +++ b/fs/ext4/inode.c
>> @@ -5279,8 +5279,9 @@ static void ext4_wait_for_tail_page_commit(struct inode *inode)
>>  {
>>  	unsigned offset;
>>  	journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
>> -	tid_t commit_tid = 0;
>> +	tid_t commit_tid;
>>  	int ret;
>> +	bool has_transaction = false;
>>  
>>  	offset = inode->i_size & (PAGE_SIZE - 1);
>>  	/*
>> @@ -5305,12 +5306,13 @@ static void ext4_wait_for_tail_page_commit(struct inode *inode)
>>  		folio_put(folio);
>>  		if (ret != -EBUSY)
>>  			return;
>> -		commit_tid = 0;
>
> We should set "has_transaction = false" here to make things work properly
> when looping... Otherwise looks good.

Ah! Good point.  I'll fix that, thanks!

Cheers,
-- 
Luís


>
> 								Honza
>
>>  		read_lock(&journal->j_state_lock);
>> -		if (journal->j_committing_transaction)
>> +		if (journal->j_committing_transaction) {
>>  			commit_tid = journal->j_committing_transaction->t_tid;
>> +			has_transaction = true;
>> +		}
>>  		read_unlock(&journal->j_state_lock);
>> -		if (commit_tid)
>> +		if (has_transaction)
>>  			jbd2_log_wait_commit(journal, commit_tid);
>>  	}
>>  }
>> 
> -- 
> Jan Kara <jack@...e.com>
> SUSE Labs, CR