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Subject: Re: [PATCH 1/2] Updated locking documentation for transaction_t
To:     Jan Kara <jack@suse.cz>
Cc:     Horst Schirmeier <horst.schirmeier@tu-dortmund.de>,
        "Theodore Ts'o" <tytso@mit.edu>, Jan Kara <jack@suse.com>,
        linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20210210095740.54881-1-alexander.lochmann@tu-dortmund.de>
 <20210210095740.54881-2-alexander.lochmann@tu-dortmund.de>
 <20210211093027.GI19070@quack2.suse.cz>
From:   Alexander Lochmann <alexander.lochmann@tu-dortmund.de>
Message-ID: <1803ac43-d6fc-4de8-78a0-7fc807f9c036@tu-dortmund.de>
Date:   Thu, 11 Feb 2021 10:53:51 +0100
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From: Alexander Lochmann <alexander.lochmann@tu-dortmund.de>
To: Jan Kara <jack@suse.cz>
Cc: Horst Schirmeier <horst.schirmeier@tu-dortmund.de>,
 Theodore Ts'o <tytso@mit.edu>, Jan Kara <jack@suse.com>,
 linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org
Message-ID: <1803ac43-d6fc-4de8-78a0-7fc807f9c036@tu-dortmund.de>
Subject: Re: [PATCH 1/2] Updated locking documentation for transaction_t
References: <20210210095740.54881-1-alexander.lochmann@tu-dortmund.de>
 <20210210095740.54881-2-alexander.lochmann@tu-dortmund.de>
 <20210211093027.GI19070@quack2.suse.cz>
In-Reply-To: <20210211093027.GI19070@quack2.suse.cz>

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On 11.02.21 10:30, Jan Kara wrote:
>>   	 */
>>   	unsigned long		t_log_start;
>>  =20
>> -	/* 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;
>=20
> So this case is actually somewhat different now that I audited the uses=
=2E
> There are two types of users - commit code (fs/jbd2/commit.c) and other=
s.
> Other users properly use j_list_lock to access t_nr_buffers. Commit cod=
e
> does not use any locks because committing transaction is fully in
> ownership of the jbd2 thread and all other users need to check & wait f=
or
> commit to be finished before doing anything with the transaction's buff=
ers.
Mhm I see.
What about '[..., no locks needed for jbd2 thread]'?

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

- Alex

--=20
Technische Universit=C3=A4t Dortmund
Alexander Lochmann                PGP key: 0xBC3EF6FD
Otto-Hahn-Str. 16                 phone:  +49.231.7556141
D-44227 Dortmund                  fax:    +49.231.7556116
http://ess.cs.tu-dortmund.de/Staff/al


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