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Date: Wed, 04 Jan 2006 20:36:25 +0200
From: Heikki Lindholm <holindho@cs.helsinki.fi>
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Subject: restore_user_regs and fpu
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Hello,

I haven't really confirmed this can happen, but I was wondering whether 
the following would be possible. Looking at restore_user_regs in 
ppc/kernel/signal_32.c and assuming:
* last_task_used_math == current, eg. a signal handler used fpu
* fpu state is still what the sig handler left there
If after the fpu state is restored to current->thread.fpr (copy_user) 
somebody preempts this task and uses fpu, wouldn't it cause the fpu 
state (of the sig handler) to be saved to 
last_task_used_math->thread.fpr overwriting the just restored state. 
Should the last_task_used_math nullifying, etc. be moved to the front of 
the function instead, or am I overlooking something?

-- Heikki Lindholm