linux-kernel - [tip:sched/core] sched/preempt, mm/fault: Decouple preemption from the page fault logic

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Date:	Tue, 19 May 2015 00:22:40 -0700
From:	tip-bot for David Hildenbrand <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	tglx@...utronix.de, peterz@...radead.org, hpa@...or.com,
	mingo@...nel.org, torvalds@...ux-foundation.org,
	linux-kernel@...r.kernel.org, dahi@...ux.vnet.ibm.com
Subject: [tip:sched/core] sched/preempt, mm/fault:
  Decouple preemption from the page fault logic

Commit-ID:  8222dbe21e79338de92d5e1956cd1e3994cc9f93
Gitweb:     http://git.kernel.org/tip/8222dbe21e79338de92d5e1956cd1e3994cc9f93
Author:     David Hildenbrand <dahi@...ux.vnet.ibm.com>
AuthorDate: Mon, 11 May 2015 17:52:20 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 19 May 2015 08:39:18 +0200

sched/preempt, mm/fault: Decouple preemption from the page fault 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.

Reviewed-and-tested-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: David Hildenbrand <dahi@...ux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: David.Laight@...LAB.COM
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: airlied@...ux.ie
Cc: akpm@...ux-foundation.org
Cc: benh@...nel.crashing.org
Cc: bigeasy@...utronix.de
Cc: borntraeger@...ibm.com
Cc: daniel.vetter@...el.com
Cc: heiko.carstens@...ibm.com
Cc: herbert@...dor.apana.org.au
Cc: hocko@...e.cz
Cc: hughd@...gle.com
Cc: mst@...hat.com
Cc: paulus@...ba.org
Cc: ralf@...ux-mips.org
Cc: schwidefsky@...ibm.com
Cc: yang.shi@...driver.com
Link: http://lkml.kernel.org/r/1431359540-32227-16-git-send-email-dahi@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 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 90786d2..ae572c1 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
 }
 
 /*
--
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