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

From: "Theodore Ts'o" <tytso@mit.edu>
To: Changheun Lee <nanich.lee@samsung.com>
Cc: alex_y_xu@yahoo.ca, axboe@kernel.dk, bgoncalv@redhat.com,
	bvanassche@acm.org, dm-crypt@saout.de, hch@lst.de,
	jaegeuk@kernel.org, linux-block@vger.kernel.org,
	linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-nvme@lists.infradead.org, ming.lei@redhat.com,
	yi.zhang@redhat.com
Subject: Re: regression: data corruption with ext4 on LUKS on nvme with torvalds master
Date: Thu, 13 May 2021 10:15:31 -0400	[thread overview]
Message-ID: <YJ00g8oBZkduQXIe@mit.edu> (raw)
In-Reply-To: <20210513094222.17635-1-nanich.lee@samsung.com>

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