Date: Sun, 19 May 2013 16:34:18 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <peterz@infradead.org>, linux-kernel@vger.kernel.org,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>, David Howells <dhowells@redhat.com>,
        Hirokazu Takata <takata@linux-m32r.org>,
        Michal Simek <monstr@monstr.eu>,
        Koichi Yasutake <yasutake.koichi@jp.panasonic.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>, Chris Metcalf <cmetcalf@tilera.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org,
        Arnd Bergmann <arnd@arndb.de>, linux-arm-kernel@lists.infradead.org,
        linux-m32r@ml.linux-m32r.org, linux-m32r-ja@ml.linux-m32r.org,
        microblaze-uclinux@itee.uq.edu.au, linux-am33-list@redhat.com,
        linuxppc-dev@lists.ozlabs.org, linux-arch@vger.kernel.org,
        linux-mm@kvack.org, kvm@vger.kernel.org
Subject: Re: [PATCH v2 10/10] kernel: might_fault does not imply might_sleep
Message-ID: <20130519133418.GA24381@redhat.com>
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On Sun, May 19, 2013 at 08:34:04AM -0400, Steven Rostedt wrote:
> On Sun, 2013-05-19 at 12:35 +0300, Michael S. Tsirkin wrote:
> 
> > No, I was not assuming that. What I'm trying to say is that a caller
> > that does something like this under a spinlock:
> > 	preempt_disable
> > 	pagefault_disable
> > 	error = copy_to_user
> > 	pagefault_enable
> > 	preempt_enable_no_resched
> > 
> > is not doing anything wrong and should not get a warning,
> > as long as error is handled correctly later.
> > Right?
> > 
> 
> What I see wrong with the above is the preempt_enable_no_resched(). The
> only place that should be ever used is right before a schedule(), as you
> don't want to schedule twice (once for the preempt_enable() and then
> again for the schedule itself).
> 
> Remember, in -rt, a spin lock does not disable preemption.
> 
> -- Steve

Right but we need to keep it working on upstream as well.
If I do preempt_enable under a spinlock upstream won't it
try to sleep under spinlock?


-- 
MST
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