linux-kernel - Re: alpha: potential race around hae_cache in RESTORE

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Message-ID: <20100927121227.GB19804@ZenIV.linux.org.uk>
Date:	Mon, 27 Sep 2010 13:12:28 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Ivan Kokshaysky <ink@...assic.park.msu.ru>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>, rth@...ddle.net,
	linux-kernel@...r.kernel.org
Subject: Re: alpha: potential race around hae_cache in RESTORE_ALL

On Mon, Sep 27, 2010 at 11:58:28AM +0400, Ivan Kokshaysky wrote:
> On Sat, Sep 25, 2010 at 08:25:09PM +0100, Al Viro wrote:
> > BTW, am I right assuming that HAE modifications is UP-only thing?  It would
> > be obviously b0rken on any SMP box, since alpha_mv is not per-CPU thing...
> 
> The only SMP system that does HAE modifications at runtime is T2, so it has
> a spinlock protection around set_hae() - see core_t2.h. Others are either
> limited to use HAE window 0 only, or do not have HAE hardware at all.

Um?  Pardon me, but that makes no sense; how would a spinlock taken in
e.g. readl() stop another process from leaving a syscall, getting to
RESTORE_ALL and overwriting HAE register while we are halfway through
the spinlock-protected area?
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