linux-ext4 - Re: regression: data corruption with ext4 on LUKS on nvme with torvalds master

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Message-ID: <YJ00g8oBZkduQXIe@mit.edu>
Date:   Thu, 13 May 2021 10:15:31 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Changheun Lee <nanich.lee@...sung.com>
Cc:     alex_y_xu@...oo.ca, axboe@...nel.dk, bgoncalv@...hat.com,
        bvanassche@....org, dm-crypt@...ut.de, hch@....de,
        jaegeuk@...nel.org, linux-block@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, ming.lei@...hat.com,
        yi.zhang@...hat.com
Subject: Re: regression: data corruption with ext4 on LUKS on nvme with
 torvalds master

On Thu, May 13, 2021 at 06:42:22PM +0900, Changheun Lee wrote:
> 
> Problem might be casued by exhausting of memory. And memory exhausting
> would be caused by setting of small bio_max_size. Actually it was not
> reproduced in my VM environment at first. But, I reproduced same problem
> when bio_max_size is set with 8KB forced. Too many bio allocation would
> be occurred by setting of 8KB bio_max_size.

Hmm... I'm not sure how to align your diagnosis with the symptoms in
the bug report.  If we were limited by memory, that should slow down
the I/O, but we should still be making forward progress, no?  And a
forced reboot should not result in data corruption, unless maybe there
was a missing check for a failed memory allocation, causing data to be
written to the wrong location, a missing error check leading to the
block or file system layer not noticing that a write had failed
(although again, memory exhaustion should not lead to failed writes;
it might slow us down, sure, but if writes are being failed, something
is Badly Going Wrong --- things like writes to the swap device or
writes by the page cleaner must succeed, or else Things Would Go Bad
In A Hurry).

						- Ted