Re: [PATCH] um: ubd: Submit all data segments atomically

From: Gabriel Krisman Bertazi <krisman@collabora.com>
To: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Cc: Martyn Welch <martyn@collabora.com>,
	richard@nod.at, jdike@addtoit.com, linux-um@lists.infradead.org,
	kernel@collabora.com,
	Christopher Obbard <chris.obbard@collabora.com>
Subject: Re: [PATCH] um: ubd: Submit all data segments atomically
Date: Wed, 18 Nov 2020 16:19:11 -0500	[thread overview]
Message-ID: <87pn4atlbk.fsf@collabora.com> (raw)
In-Reply-To: <7c1bf8c3-0e80-ab90-778c-c124fab3f747@cambridgegreys.com> (Anton Ivanov's message of "Mon, 26 Oct 2020 09:25:51 +0000")

Anton Ivanov <anton.ivanov@cambridgegreys.com> writes:

> On 25/10/2020 04:41, Gabriel Krisman Bertazi wrote:
>> Internally, UBD treats each physical IO segment as a separate command to
>> be submitted in the execution pipe.  If the pipe returns a transient
>> error after a few segments have already been written, UBD will tell the
>> block layer to requeue the request, but there is no way to reclaim the
>> segments already submitted.  When a new attempt to dispatch the request
>> is done, those segments already submitted will get duplicated, causing
>> the WARN_ON below in the best case, and potentially data corruption.
>> In my system, running a UML instance with 2GB of RAM and a 50M UBD
>> disk,

>>   [...]
>> ---[ end trace c6e7444e55386c0f ]---
>> Cc: Christopher Obbard <chris.obbard@collabora.com>
>> Reported-by: Martyn Welch <martyn@collabora.com>
>> Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>

> Acked-By: Anton Ivanov <anton.ivanov@cambridgegreys.com>

Hi,

Is this queued somewhere?  I've been watching the linux-next branch of
rw's tree.  Is that the right tree?

Thanks,

-- 
Gabriel Krisman Bertazi

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