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Re: [PATCH] xfs: fix in the setting of logbsize

To: Ales Novak <alnovak@xxxxxxx>
Subject: Re: [PATCH] xfs: fix in the setting of logbsize
From: Mark Tinguely <tinguely@xxxxxxx>
Date: Mon, 08 Jun 2015 08:04:39 -0500
Cc: Dave Chinner <david@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <alpine.LSU.2.03.1506071054580.20732@xxxxxxx>
References: <1433510925-11438-1-git-send-email-alnovak@xxxxxxx> <20150605222257.GY24666@dastard> <alpine.LSU.2.03.1506071054580.20732@xxxxxxx>
User-agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:9.0) Gecko/20120122 Thunderbird/9.0
On 06/07/15 04:16, Ales Novak wrote:

On 2015-6-6 00:22, Dave Chinner wrote:

Can you give more information about the crashes? From this
description, I do not know whether this is a work around or a fix
because I don't know what code is actually causing the problem or
the circumstances in which the crash occurs. Hence I cannot
determine if your change is the right change to make or whether the
documetnation is simply wrong and we have a real bug we shoul dbe
fixing.

The crashes occurred with logsunit=192k and logbsize=256k. xlog_sync()
is calculating in logsunit units:

count = XLOG_LSUNITTOB(log, XLOG_BTOLSUNIT(log, count_init));

With count_init=256k, the calculated roundoff will try to cover that in
two 192k units. This roundoff is passed to the xlog_pack_data() which
walks the buffer and (hopefully) fails when it hits its 256k border.


Talked about this once before:

 http://oss.sgi.com/archives/xfs/2013-03/msg00039.html

Mark.

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