Received-SPF: pass (google.com: domain of linux-ext4-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Fri, 14 May 2021 05:50:40 -0400 (EDT)
From:   Mikulas Patocka <mpatocka@redhat.com>
To:     Milan Broz <gmazyland@gmail.com>,
        Bart Van Assche <bvanassche@acm.org>,
        "Theodore Ts'o" <tytso@mit.edu>,
        Changheun Lee <nanich.lee@samsung.com>
cc:     alex_y_xu@yahoo.ca, axboe@kernel.dk, bgoncalv@redhat.com,
        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, dm-devel@redhat.com
Subject: Re: regression: data corruption with ext4 on LUKS on nvme with
 torvalds master
In-Reply-To: <alpine.LRH.2.02.2105131510330.21927@file01.intranet.prod.int.rdu2.redhat.com>
Message-ID: <alpine.LRH.2.02.2105140544010.22439@file01.intranet.prod.int.rdu2.redhat.com>
References: <a01ab479-69e8-9395-7d24-9de1eec28aff@acm.org> <0e7b0b6e-e78c-f22d-af8d-d7bdcb597bea@gmail.com> <alpine.LRH.2.02.2105131510330.21927@file01.intranet.prod.int.rdu2.redhat.com>
User-Agent: Alpine 2.02 (LRH 1266 2009-07-14)
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Precedence: bulk


On 5/13/21 7:15 AM, Theodore Ts'o wrote:
> 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

If you use data=writeback, data writes and journal writes are not 
synchronized. So, it may be possible that a journal write made it through, 
a data write didn't - the end result would be a file containing random 
contents that was on the disk.

Changheun - do you use data=writeback? Did the corruption happen only in 
newly created files? Or did it corrupt existing files?

> 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).

Mikulas