linux-ext4 - Re: [PATCH 1/2] Updated locking documentation for transaction

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Date:   Thu, 11 Feb 2021 10:53:51 +0100
From:   Alexander Lochmann <alexander.lochmann@...dortmund.de>
To:     Jan Kara <jack@...e.cz>
Cc:     Horst Schirmeier <horst.schirmeier@...dortmund.de>,
        "Theodore Ts'o" <tytso@....edu>, Jan Kara <jack@...e.com>,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] Updated locking documentation for transaction_t



On 11.02.21 10:30, Jan Kara wrote:
>>   	 */
>>   	unsigned long		t_log_start;
>>   
>> -	/* Number of buffers on the t_buffers list [j_list_lock] */
>> +	/* Number of buffers on the t_buffers list [j_list_lock, no lock for quick racy checks] */
>>   	int			t_nr_buffers;
> 
> So this case is actually somewhat different now that I audited the uses.
> There are two types of users - commit code (fs/jbd2/commit.c) and others.
> Other users properly use j_list_lock to access t_nr_buffers. Commit code
> does not use any locks because committing transaction is fully in
> ownership of the jbd2 thread and all other users need to check & wait for
> commit to be finished before doing anything with the transaction's buffers.
Mhm I see.
What about '[..., no locks needed for jbd2 thread]'?

How do the others wait for the commit to be finished?

- Alex

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