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

tip-bot for David Hildenbrand
2015-05-19T07:23:18Z

Commit-ID: 8222dbe21e79338de92d5e1956cd1e3994cc9f93
Gitweb: http://git.kernel.org/tip/8222dbe21e79338de92d5e1956cd1e3994cc9f93
Author: David Hildenbrand <dahi@linux.vnet.ibm.com>
AuthorDate: Mon, 11 May 2015 17:52:20 +0200
Committer: Ingo Molnar <mingo@kernel.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@linutronix.de>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: David.Laight@ACULAB.COM
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: airlied@linux.ie
Cc: akpm@linux-foundation.org
Cc: benh@kernel.crashing.org
Cc: bigeasy@linutronix.de
Cc: borntraeger@de.ibm.com
Cc: daniel.vetter@intel.com
Cc: heiko.carstens@de.ibm.com
Cc: herbert@gondor.apana.org.au
Cc: hocko@suse.cz
Cc: hughd@google.com
Cc: mst@redhat.com
Cc: paulus@samba.org
Cc: ralf@linux-mips.org
Cc: schwidefsky@de.ibm.com
Cc: yang.shi@windriver.com
Link: http://lkml.kernel.org/r/1431359540-32227-16-git-send-email-dahi@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.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
}

/*