linux-kernel - RE: [PATCH 0/1] Fixup write permission of TLB on powerpc e500 core

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Date:	Fri, 15 Jul 2011 11:32:49 +0100
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Shan Hai" <haishan.bai@...il.com>,
	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>
Cc:	<tony.luck@...el.com>, <linux-kernel@...r.kernel.org>,
	<cmetcalf@...era.com>, <dhowells@...hat.com>, <paulus@...ba.org>,
	<tglx@...utronix.de>, <walken@...gle.com>,
	<linuxppc-dev@...ts.ozlabs.org>, <akpm@...ux-foundation.org>
Subject: RE: [PATCH 0/1] Fixup write permission of TLB on powerpc e500 core

 
> The fault causing futex_atomic_cmpxchg_inatomic() is
> protected by pagefault_disable(), so the page fault handler has
> no chance to toggle the SW dirty/young tracking.

Perhaps that is the bug!
Whatever pagefault_disable() does, it shouldn't disable the
SW dirty/young tracking - which should only needs bits moving
in the page table itself (and TLB update??) rather than any
operations on the rest of the data areas.

It looks to me as though this could happen any time a page
is marked inaccessible by the dirty/young tracking.
Not just as a result of COW.

	David


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