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Subject: Re: BUG: Global FPU corruption in 2.2
To: torvalds@transmeta.com (Linus Torvalds)
Date: Tue, 24 Apr 2001 17:25:20 +0100 (BST)
Cc: linux-kernel@vger.kernel.org
In-Reply-To: <9c48gv$fbk$1@penguin.transmeta.com> from "Linus Torvalds" at Apr 24, 2001 09:10:07 AM
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From: Alan Cox <alan@lxorguk.ukuu.org.uk>
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> >1.) If I'm not mistaken switch_to changes current->flags without
> >atomic operations and without any locks and sys_ptrace changes
> >child->flags only protected by the big kernel lock.
> 
> ptrace only operates on processes that are stopped. So there are no
> locking issues - we've synchronized on a much higher level than a
> spinlock or semaphore.

In the 2.2 case the ptrace flags themselves are in the same flag set as
the PF_ flags. In 2.4 that was fixed. That means there are some bizarre cases
where current->flags might not be handled perfectly.