linux-kernel - [PATCH RFC 15/15] uaccess: decouple preemption from the pagefault logic

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Message-Id: <1430934639-2131-16-git-send-email-dahi@linux.vnet.ibm.com>
Date:	Wed,  6 May 2015 19:50:39 +0200
From:	David Hildenbrand <dahi@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	dahi@...ux.vnet.ibm.com, mingo@...hat.com, peterz@...radead.org,
	yang.shi@...driver.com, bigeasy@...utronix.de,
	benh@...nel.crashing.org, paulus@...ba.org,
	akpm@...ux-foundation.org, heiko.carstens@...ibm.com,
	schwidefsky@...ibm.com, borntraeger@...ibm.com, mst@...hat.com,
	tglx@...utronix.de, David.Laight@...LAB.COM, hughd@...gle.com,
	hocko@...e.cz, ralf@...ux-mips.org, herbert@...dor.apana.org.au,
	linux@....linux.org.uk, airlied@...ux.ie, daniel.vetter@...el.com,
	linux-mm@...ck.org, linux-arch@...r.kernel.org
Subject: [PATCH RFC 15/15] uaccess: decouple preemption from the pagefault logic

As the fault handlers now all rely on the pagefault_disabled() checks
and implicit preempt_disable() calls by pagefault_disable() have been
made explicit, we can completely rely on the pagefault_disableD counter.

So let's no longer touch the preempt count when disabling/enabling
pagefaults. After a call to pagefault_disable(), pagefault_disabled()
will return true, but in_atomic() won't.

Signed-off-by: David Hildenbrand <dahi@...ux.vnet.ibm.com>
---
 include/linux/uaccess.h | 16 ++--------------
 1 file changed, 2 insertions(+), 14 deletions(-)

diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 23290cc..83f2a7b 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -1,7 +1,6 @@
 #ifndef __LINUX_UACCESS_H__
 #define __LINUX_UACCESS_H__
 
-#include <linux/preempt.h>
 #include <linux/sched.h>
 #include <asm/uaccess.h>
 
@@ -20,17 +19,11 @@ static __always_inline void pagefault_disabled_dec(void)
  * These routines enable/disable the pagefault handler. If disabled, it will
  * not take any locks and go straight to the fixup table.
  *
- * We increase the preempt and the pagefault count, to be able to distinguish
- * whether we run in simple atomic context or in a real pagefault_disable()
- * context.
- *
- * For now, after pagefault_disabled() has been called, we run in atomic
- * context. User access methods will not sleep.
- *
+ * User access methods will not sleep when called from a pagefault_disabled()
+ * environment.
  */
 static inline void pagefault_disable(void)
 {
-	preempt_count_inc();
 	pagefault_disabled_inc();
 	/*
 	 * make sure to have issued the store before a pagefault
@@ -47,11 +40,6 @@ static inline void pagefault_enable(void)
 	 */
 	barrier();
 	pagefault_disabled_dec();
-#ifndef CONFIG_PREEMPT
-	preempt_count_dec();
-#else
-	preempt_enable();
-#endif
 }
 
 /*
-- 
2.1.4

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