linux-kernel - Why does test_bit() take a volatile addr?

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Message-ID: <87ioy11k8s.fsf@rustcorp.com.au>
Date:	Mon, 16 Sep 2013 13:38:35 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	<torvalds@...ux-foundation.org>
Cc:	"LKML" <linux-kernel@...r.kernel.org>
Subject: Why does test_bit() take a volatile addr?

Predates git, does anyone remember the rationale?

ie:
        int test_bit(int nr, const volatile unsigned long *addr)

I noticed because gcc failed to elimiate some code in a patch I was
playing with.

I'm nervous about subtle bugs involved in ripping it out, even if noone
knows why.  Should I add __test_bit()?

Thanks,
Rusty.
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