From: Russell King - ARM Linux <linux@armlinux.org.uk>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Vineet Gupta <Vineet.Gupta1@synopsys.com>,
Nicolas Pitre <nicolas.pitre@linaro.org>,
Andrew Morton <akpm@linux-foundation.org>,
David Hildenbrand <dahi@linux.vnet.ibm.com>,
Thomas Petazzoni <thomas.petazzoni@free-electrons.com>,
lkml <linux-kernel@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>
Subject: Re: kmap_atomic and preemption
Date: Wed, 4 May 2016 20:17:55 +0100 [thread overview]
Message-ID: <20160504191755.GV19428@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <20160504134729.GP3430@twins.programming.kicks-ass.net>
On Wed, May 04, 2016 at 03:47:29PM +0200, Peter Zijlstra wrote:
> Traditionally kmap_atomic() disables preemption; and the reason is that
> the returned pointer must stay valid. This had a side effect in that it
> also disabled pagefaults.
A lowmem page should never change its page_address(), so that much is
safe. I think the question is whether there is any driver code which
assumes that preemption is unconditionally disabled between a
kmap_atomic() has been called.
That wouldn't be an unreasonable assumption given the name of the
function, so I'd suggest caution with making kmap_atomic() have these
kinds of differing behaviours depending on whether we're asking to
kmap a high or lowmem page.
If we are going to allow this, I think it at least needs to be well
documented.
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next prev parent reply other threads:[~2016-05-04 19:20 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-04 10:37 kmap_atomic and preemption Vineet Gupta
2016-05-04 13:47 ` Peter Zijlstra
2016-05-04 13:53 ` Thomas Petazzoni
2016-05-04 14:01 ` Vineet Gupta
2016-05-04 14:16 ` Vineet Gupta
2016-05-04 15:01 ` Peter Zijlstra
2016-05-05 12:37 ` Vineet Gupta
2016-05-04 19:17 ` Russell King - ARM Linux [this message]
2016-05-05 9:37 ` Peter Zijlstra
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