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

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Message-ID: <20240724091713.e4w2hskcybulz27z@quack3>
Date: Wed, 24 Jul 2024 11:17:13 +0200
From: Jan Kara <jack@...e.cz>
To: "Luis Henriques (SUSE)" <luis.henriques@...ux.dev>
Cc: Theodore Ts'o <tytso@....edu>, Andreas Dilger <adilger@...ger.ca>,
	Jan Kara <jack@...e.cz>,
	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 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.

								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