linux-ext4 - [QUESTION] Locking for the transaction buffers

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Date:   Mon, 18 Dec 2017 18:08:34 +0100
From:   Alexander Lochmann <alexander.lochmann@...dortmund.de>
To:     linux-ext4@...r.kernel.org
Cc:     Horst Schirmeier <horst.schirmeier@...dortmund.de>
Subject: [QUESTION] Locking for the transaction buffers

Hi developers,

I'm studying the locking in the JBD2 subsystem (v4.15-rc4). Doing so, I
came across the jbd2_journal_commit_transaction function
where severals lists, e.g., t_forget or t_buffers, are flushed in a
while loop.
According to the documentation in inlcude/linux/jbd2.h, the j_list_lock
lock is the appropriate lock.
However, it is only used in one out of three cases:
In fs/jbd2/commit.c:903, the while loop is protected using the
j_list_lock lock. Whereas it is not used at line 464 and 561.
In contrast to that, the insert and remove operations to any of these
lists are protected by that lock.

Can you please tell me why that lock is not used at line 464 and 561?

Thanks in advance!

Regards,
Alex

-- 
Technische Universität Dortmund
Alexander Lochmann                PGP key: 0xBC3EF6FD
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