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Date: Thu, 6 Mar 2014 15:33:04 +0100 (CET) From: Thomas Gleixner <tglx@...utronix.de> To: Peter Zijlstra <peterz@...radead.org> cc: Rasmus Villemoes <linux@...musvillemoes.dk>, "H. Peter Anvin" <hpa@...or.com>, Khalid Aziz <khalid.aziz@...cle.com>, Ingo Molnar <mingo@...nel.org>, akpm@...ux-foundation.org, andi.kleen@...el.com, rob@...dley.net, viro@...iv.linux.org.uk, oleg@...hat.com, venki@...gle.com, linux-kernel@...r.kernel.org Subject: Re: [RFC] [PATCH] Pre-emption control for userspace On Thu, 6 Mar 2014, Peter Zijlstra wrote: > On Thu, Mar 06, 2014 at 02:45:00PM +0100, Rasmus Villemoes wrote: > > Peter Zijlstra <peterz@...radead.org> writes: > > > > > On Thu, Mar 06, 2014 at 02:24:43PM +0100, Rasmus Villemoes wrote: > > >> Is it possible to implement non-sleeping versions of {get,put}_user()? > > > > > > __{get,put}_user() > > > > Huh? > > > > arch/x86/include/asm/uaccess.h: > > > > /** > > * __get_user: - Get a simple variable from user space, with less checking. > > * @x: Variable to store result. > > * @ptr: Source address, in user space. > > * > > * Context: User context only. This function may sleep. > > > > What am I missing? > > __get_user() -> __get_user_nocheck() -> __get_user_size() -> __get_user_asm() > > And __get_user_asm() seems to generate the required .fixup section for > this to work in pagefault_disable() context. Well, it still might sleep if you're using it in page fault enabled context. So the documentation of that function sucks. Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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