linux-kernel - Re: [PATCH] pci-dma: Fix x86 dma_alloc_coherent to fully clear all pages returned

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Message-ID: <20150218203909.GE13991@two.firstfloor.org>
Date:	Wed, 18 Feb 2015 21:39:09 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Tim Chen <tim.c.chen@...ux.intel.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>, "H. Peter Anvin" <hpa@...or.com>,
	Akinobu Mita <akinobu.mita@...il.com>,
	Mathias Nyman <mathias.nyman@...ux.intel.com>,
	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	linux-usb@...r.kernel.org, stable <stable@...r.kernel.org>,
	torvalds@...ux-foundation.org
Subject: Re: [PATCH] pci-dma: Fix x86 dma_alloc_coherent to fully clear all
 pages returned

> > Have you tried doing the experiments I suggested in
> > 
> >         http://marc.info/?l=linux-usb&m=142272448620716&w=2
> > 
> > to determine where the problem occurs?
> > 
> 
> I was bogged down with other things lately and I haven't got a chance to
> test that.  But as you said, there's very few places where xhci 
> call this memory allocation.  So I think the problem has been fairly
> narrowed down for the XHCI folks.

Also I don't really understand why we're even discussing this. The patch
only makes an widely used API behave as it was before. Who knows who
else was broken with this change. There's no sane way to audit all
users. There is no real advantage of the new behavior.

The only good way is to revert to old behavior, like in Tim's
original patch. And doing it quickly for mainline and stable.

FWIW we have a large number of systems here that are broken
without this change.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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