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Date: Sat, 2 Aug 2003 11:39:07 -0700
From: Andrew Morton <akpm@osdl.org>
To: Zwane Mwaikambo <zwane@arm.linux.org.uk>
Cc: oxymoron@waste.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] [1/2] random: SMP locking
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Zwane Mwaikambo <zwane@arm.linux.org.uk> wrote:
>
> Perhaps might_sleep() in *_user, copy_* etc is in order?

Probably, with a little care.

A userspace copy while in an atomic region is actually legal, on behalf of
the read() and write() pagecache copy functions: if we take a fault while
holding an atomic kmap, the fault handler bales and the usercopy returns a
short copy.

In other words: if you stick a might_sleep() in __copy_from_user() and
__copy_to_user() you get a false positive on every read() and write().

We could probably add it to copy_to_user() and copy_from_user() though.