linux-ext4 - jbd2: fix deadlock while checkpoint thread waits commit thread to finish (backport to 4.14)

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Date:   Wed, 7 Jul 2021 21:42:25 +0300
From:   Ivan Zahariev <famzah@...zah.net>
To:     linux-ext4@...r.kernel.org
Subject: jbd2: fix deadlock while checkpoint thread waits commit thread to
 finish (backport to 4.14)

Hello,

We're running Linux kernel 4.14.x and our systems occasionally suffer a 
bug which is already fixed: 
https://github.com/torvalds/linux/commit/53cf978457325d8fb2cdecd7981b31a8229e446e

This bugfix hasn't been ported to Linux kernels 4.14 or 4.19. The patch 
applies cleanly. The two files "fs/jbd2/checkpoint.c" and 
"fs/jbd2/journal.c" seem pretty identical in the affected sections 
compared to kernel 5.4 where we have this bugfix already applied.

Is it on purpose that this bugfix hasn't been ported to 4.14? Is it safe 
that we backport it manually in our kernel 4.14 builds? Or is the "ext4" 
system in 4.14 and 5.4 fundamentally different and this would lead to 
data loss or other problems?

Thank you.

Best regards.
--Ivan