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Subject: Re: [PATCH 1/3] futex: do not pagefault_disable in
 futex_atomic_cmpxchg_inatomic()
From: Peter Zijlstra <peterz@infradead.org>
To: Darren Hart <darren@dvhart.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
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On Sun, 2011-03-13 at 17:55 -0700, Darren Hart wrote:
> I wondered about the preempt vs pagefault disable 

In current mainline they happen to be the same, but for -rt they're not.

Its also conceptually different, with preempt disable we dis-allow any
scheduling, which thus also precludes most fault handlers.

Disabling pagefault can be done without also disabling preemption (as is
done in -rt) and simply means that we'll never try to handle the fault
and fallback to the exception table or give up and segfault the kernel.

Its not dis-similar to the whole rcu_read_lock() vs preempt_disable()
stuff, for a while one implied the other.
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