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

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Date:	Wed, 22 May 2013 15:59:01 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	"Michael S. Tsirkin" <mst@...hat.com>
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 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
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