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

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH] xfs: fix in the setting of logbsize
From: Ales Novak <alnovak@xxxxxxx>
Date: Sun, 7 Jun 2015 11:16:28 +0200 (CEST)
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20150605222257.GY24666@dastard>
References: <1433510925-11438-1-git-send-email-alnovak@xxxxxxx> <20150605222257.GY24666@dastard>
User-agent: Alpine 2.03 (LSU 1266 2009-07-14)

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.

--
Ales Novak

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