linux-kernel - Re: [PANIC, hyperv] BUG: unable to handle kernel paging request at ffff880077800004 (hv_ringbuffer

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Message-ID: <20140829094945.GA5122@mwanda>
Date:	Fri, 29 Aug 2014 12:49:45 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	KY Srinivasan <kys@...rosoft.com>
Cc:	Sitsofe Wheeler <sitsofe@...il.com>,
	Dexuan Cui <decui@...rosoft.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>
Subject: Re: [PANIC, hyperv] BUG: unable to handle kernel paging request at
 ffff880077800004 (hv_ringbuffer_write)

It's sort of weird that this is an alignment issue.  The config that
was posted earlier was an x86_64 config and on that system then the
pointers from kmalloc() should already be aligned correctly at
sizeof(u64).

Earlier I said I suspected the code is racy, so possibly changing from
kmalloc() to get_zeroed_page() just changes the timing enough so we
don't see the race condition.

regards,
dan carpenter

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