From: Alexander Lochmann <alexander.lochmann@tu-dortmund.de>
To: "Theodore Ts'o" <tytso@mit.edu>,
Horst Schirmeier <horst.schirmeier@tu-dortmund.de>,
Jan Kara <jack@suse.com>,
linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [v2] Updated locking documentation for transaction_t
Date: Mon, 8 Apr 2019 10:32:35 +0200 [thread overview]
Message-ID: <ec3b972e-8342-8359-448d-3efaa476d5b3@tu-dortmund.de> (raw)
In-Reply-To: <20190407165206.GA11370@mit.edu>
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Thanks, Ted, for your feedback!
I'll submit a modified version.
- Alex
On 07.04.19 18:52, Theodore Ts'o wrote:
> On Mon, Mar 18, 2019 at 07:42:37PM +0100, Alexander Lochmann wrote:
>> /*t
>> - * Where in the log does this transaction's commit start? [no locking]
>> + * Where in the log does this transaction's commit start?
>> + * [journal_t.j_state_lock]
>> */
>> unsigned long t_log_start;
>
> Well, technically, that's not quite right. It's only assigned in one
> location, and we hold j_state_lock, yes. But that's because we need
> to access journal->j_head. At the point where we set t_log_start, the
> transaction has already been locked down (transaction->t_state >
> T_LOCKED).
>
> Similarly, we happen to be holding j_state where it is currently being
> accessed, but it's not because we needed the lock in order to access
> t_log_start safely.
>
>> /*
>> - * When transaction started
>> + * When transaction started [journal_t.j_state_lock]
>> */
>> unsigned long t_start;
>
> And again, not really. The primary place where t_start is set is when
> the transaction is firstt created, before it's visible anywhere else.
> after that, it is used exclusively by the commit thread, and so no
> locking is necessary. It's true that in the places where it is used,
> j_state_lock happens to be taken, but it's strictly not necessary.
>
>>
>> /*
>> - * When commit was requested
>> + * When commit was requested [journal_t.j_state_lock]
>> */
>> unsigned long t_requested;
>
> Yes, that appears to be correct.
>
>>
>> /*
>> - * Checkpointing stats [j_checkpoint_sem]
>> + * Checkpointing stats [journal_t.j_list_lock]
>> */
>> struct transaction_chp_stats_s t_chp_stats;
>>
>
> This appears to be correct.
>
> - Ted
>
--
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prev parent reply other threads:[~2019-04-08 8:32 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-18 18:42 [PATCH v2] Updated locking documentation for transaction_t Alexander Lochmann
2019-03-19 8:33 ` Jan Kara
2019-04-07 16:52 ` [v2] " Theodore Ts'o
2019-04-08 8:32 ` Alexander Lochmann [this message]
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