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Date:   Fri, 19 Mar 2021 11:16:53 -0400
From:   "Theodore Ts'o" <tytso@mit.edu>
To:     Shashidhar Patil <shashidhar.patil@gmail.com>
Cc:     linux-ext4@vger.kernel.org
Subject: Re: jbd2 task hung in jbd2_journal_commit_transaction
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On Thu, Mar 18, 2021 at 12:27:44PM +0530, Shashidhar Patil wrote:
> Hi Theodore,
>     I forgot to include two important  details , the stack trace of
> loop0 driver and sar output, which clearly nail  the problem.
> The losetup with Ubuntu16.05 does not have O_DIRECT support  and we
> were not aware of bypassing of journalling if
> O_DIRECT combined with preallocated file scenario.

Which version of the kernel are you using?  The use of O_DIRECT for
loop devices requires kernel and losetup support.  (Also note that
upstream developers really generally don't pay attention --- or
support --- distribution kernels unless they work for the company for
which you are paying $$$ for support, and Ubuntu 16.05 isn't even a
Long-Term Support distribution.)

My suggestion is to see if you can replicate the problem on a modern
userspace with the latest kernel.  And if not, then that's an object
lesson about why using a antediluvian is not a great life choice.  :-)

Cheers,

						- Ted