linux-kernel - Re: [PATCH v2 07/10] powerpc: uaccess s/might_sleep/might

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Message-ID: <20130524130032.GA10167@redhat.com>
Date:	Fri, 24 May 2013 16:00:32 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-kernel@...r.kernel.org,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	David Howells <dhowells@...hat.com>,
	Hirokazu Takata <takata@...ux-m32r.org>,
	Michal Simek <monstr@...str.eu>,
	Koichi Yasutake <yasutake.koichi@...panasonic.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Chris Metcalf <cmetcalf@...era.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-arm-kernel@...ts.infradead.org, linux-m32r@...linux-m32r.org,
	linux-m32r-ja@...linux-m32r.org, microblaze-uclinux@...e.uq.edu.au,
	linux-am33-list@...hat.com, linuxppc-dev@...ts.ozlabs.org,
	linux-arch@...r.kernel.org, linux-mm@...ck.org, kvm@...r.kernel.org
Subject: Re: [PATCH v2 07/10] powerpc: uaccess s/might_sleep/might_fault/

On Wed, May 22, 2013 at 03:59:01PM +0200, Arnd Bergmann wrote:
> On Thursday 16 May 2013, Michael S. Tsirkin wrote:
> > @@ -178,7 +178,7 @@ do {                                                                \
> >         long __pu_err;                                          \
> >         __typeof__(*(ptr)) __user *__pu_addr = (ptr);           \
> >         if (!is_kernel_addr((unsigned long)__pu_addr))          \
> > -               might_sleep();                                  \
> > +               might_fault();                                  \
> >         __chk_user_ptr(ptr);                                    \
> >         __put_user_size((x), __pu_addr, (size), __pu_err);      \
> >         __pu_err;                                               \
> > 
> 
> Another observation:
> 
> 	if (!is_kernel_addr((unsigned long)__pu_addr))
> 		might_sleep();
> 
> is almost the same as
> 
> 	might_fault();
> 
> except that it does not call might_lock_read().
> 
> The version above may have been put there intentionally and correctly, but
> if you want to replace it with might_fault(), you should remove the
> "if ()" condition.
> 
> 	Arnd

Well not exactly. The non-inline might_fault checks the
current segment, not the address.
I'm guessing this is trying to do the same just without
pulling in segment_eq, but I'd like a confirmation
from more PPC maintainers.

Guys would you ack

- 	if (!is_kernel_addr((unsigned long)__pu_addr))
- 		might_fault();
+ 	might_fault();

on top of this patch?

Also, any volunteer to test this (not just test-build)?

-- 
MST
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