From: Peter Zijlstra <peterz@infradead.org>
To: David Miller <davem@davemloft.net>
Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
sparclinux@vger.kernel.org
Subject: Re: [PATCH 0/4]: Respin local_irq_*_nmi() stuff.
Date: Tue, 13 Apr 2010 10:37:14 +0200 [thread overview]
Message-ID: <1271147834.4807.980.camel@twins> (raw)
In-Reply-To: <20100413.005640.48990319.davem@davemloft.net>
On Tue, 2010-04-13 at 00:56 -0700, David Miller wrote:
> If we are in an NMI then doing a plain raw_local_irq_disable() will
> write PIL_NORMAL_MAX into %pil, which is lower than PIL_NMI, and thus
> we'll re-enable NMIs and recurse.
>
> Doing a simple:
>
> %pil = %pil | PIL_NORMAL_MAX
>
> does what we want, if we're already at PIL_NMI (15) we leave it at
> that setting, else we set it to PIL_NORMAL_MAX (14).
Ah indeed, and without a conditional, very nice!
It does rely on the exact values of the PIL_levels, it might make sense
to note that in the comment, something like:
* Assumes: PIL_NMI | PIL_NORMAL_MAX == PIL_NMI.
Hmm, it also assumes %pil is never anything other than 0,
PIL_NORMAL_MAX, PIL_NMI, because if:
(%pil & 1) && (%pil != PIL_NMI)
then you'll end up disabling NMIs. Could something like that ever
happen?
WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: David Miller <davem@davemloft.net>
Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
sparclinux@vger.kernel.org
Subject: Re: [PATCH 0/4]: Respin local_irq_*_nmi() stuff.
Date: Tue, 13 Apr 2010 08:37:14 +0000 [thread overview]
Message-ID: <1271147834.4807.980.camel@twins> (raw)
In-Reply-To: <20100413.005640.48990319.davem@davemloft.net>
On Tue, 2010-04-13 at 00:56 -0700, David Miller wrote:
> If we are in an NMI then doing a plain raw_local_irq_disable() will
> write PIL_NORMAL_MAX into %pil, which is lower than PIL_NMI, and thus
> we'll re-enable NMIs and recurse.
>
> Doing a simple:
>
> %pil = %pil | PIL_NORMAL_MAX
>
> does what we want, if we're already at PIL_NMI (15) we leave it at
> that setting, else we set it to PIL_NORMAL_MAX (14).
Ah indeed, and without a conditional, very nice!
It does rely on the exact values of the PIL_levels, it might make sense
to note that in the comment, something like:
* Assumes: PIL_NMI | PIL_NORMAL_MAX = PIL_NMI.
Hmm, it also assumes %pil is never anything other than 0,
PIL_NORMAL_MAX, PIL_NMI, because if:
(%pil & 1) && (%pil != PIL_NMI)
then you'll end up disabling NMIs. Could something like that ever
happen?
next prev parent reply other threads:[~2010-04-13 8:37 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-04-09 23:01 [PATCH 0/4]: Respin local_irq_*_nmi() stuff David Miller
2010-04-09 23:01 ` David Miller
2010-04-13 5:08 ` David Miller
2010-04-13 5:08 ` David Miller
2010-04-13 7:48 ` Peter Zijlstra
2010-04-13 7:48 ` Peter Zijlstra
2010-04-13 7:56 ` David Miller
2010-04-13 7:56 ` David Miller
2010-04-13 7:56 ` David Miller
2010-04-13 8:37 ` Peter Zijlstra [this message]
2010-04-13 8:37 ` Peter Zijlstra
2010-04-13 8:46 ` David Miller
2010-04-13 8:46 ` David Miller
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