From mboxrd@z Thu Jan  1 00:00:00 1970
From: mst@redhat.com (Michael S. Tsirkin)
Date: Sun, 19 May 2013 19:40:09 +0300
Subject: [PATCH v2 10/10] kernel: might_fault does not imply might_sleep
In-Reply-To: <1368979579.6828.114.camel@gandalf.local.home>
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Message-ID: <20130519164009.GA2434@redhat.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Sun, May 19, 2013 at 12:06:19PM -0400, Steven Rostedt wrote:
> On Sun, 2013-05-19 at 16:34 +0300, Michael S. Tsirkin wrote:
> 
> > 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?
> 
> No it wont. A spinlock calls preempt_disable implicitly, and a
> preempt_enable() will not schedule unless preempt_count is zero, which
> it wont be under a spinlock.
> 
> If it did, there would be lots of bugs all over the place because this
> is done throughout the kernel (a preempt_enable() under a spinlock).
> 
> In other words, don't ever use preempt_enable_no_resched().
> 
> -- Steve
> 


OK I get it. So let me correct myself. The simple code
that does something like this under a spinlock:
>       preempt_disable
>       pagefault_disable
>       error = copy_to_user
>       pagefault_enable
>       preempt_enable
>
is not doing anything wrong and should not get a warning,
as long as error is handled correctly later.
Right?