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Commit 8bcbde54 authored by David Hildenbrand's avatar David Hildenbrand Committed by Ingo Molnar
Browse files

sched/preempt, mm/fault: Count pagefault_disable() levels in pagefault_disabled 



Until now, pagefault_disable()/pagefault_enabled() used the preempt
count to track whether in an environment with pagefaults disabled (can
be queried via in_atomic()).

This patch introduces a separate counter in task_struct to count the
level of pagefault_disable() calls. We'll keep manipulating the preempt
count to retain compatibility to existing pagefault handlers.

It is now possible to verify whether in a pagefault_disable() envionment
by calling pagefault_disabled(). In contrast to in_atomic() it will not
be influenced by preempt_enable()/preempt_disable().

This patch is based on a patch from Ingo Molnar.

Reviewed-and-tested-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarDavid Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: default avatarPeter 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/1431359540-32227-2-git-send-email-dahi@linux.vnet.ibm.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 3e51f3c4

include/linux/sched.h

+1 −0
Original line number Diff line number Diff line
@@ -1788,6 +1788,7 @@ struct task_struct { 
#ifdef CONFIG_DEBUG_ATOMIC_SLEEP

	unsigned long	task_state_change;

#endif

	int pagefault_disabled;

};



/* Future-safe accessor for struct task_struct's cpus_allowed. */

include/linux/uaccess.h

+29 −7
Original line number Diff line number Diff line
@@ -2,20 +2,36 @@ 
#define __LINUX_UACCESS_H__



#include <linux/preempt.h>

#include <linux/sched.h>

#include <asm/uaccess.h>



static __always_inline void pagefault_disabled_inc(void)

{

	current->pagefault_disabled++;

}



static __always_inline void pagefault_disabled_dec(void)

{

	current->pagefault_disabled--;

	WARN_ON(current->pagefault_disabled < 0);

}



/*

 * These routines enable/disable the pagefault handler in that

 * it will not take any locks and go straight to the fixup table.

 * 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.

 *

 * They have great resemblance to the preempt_disable/enable calls

 * and in fact they are identical; this is because currently there is

 * no other way to make the pagefault handlers do this. So we do

 * disable preemption but we don't necessarily care about that.

 */

static inline void pagefault_disable(void)

{

	preempt_count_inc();

	pagefault_disabled_inc();

	/*

	 * make sure to have issued the store before a pagefault

	 * can hit.
@@ -25,18 +41,24 @@ static inline void pagefault_disable(void) 


static inline void pagefault_enable(void)

{

#ifndef CONFIG_PREEMPT

	/*

	 * make sure to issue those last loads/stores before enabling

	 * the pagefault handler again.

	 */

	barrier();

	pagefault_disabled_dec();

#ifndef CONFIG_PREEMPT

	preempt_count_dec();

#else

	preempt_enable();

#endif

}



/*

 * Is the pagefault handler disabled? If so, user access methods will not sleep.

 */

#define pagefault_disabled() (current->pagefault_disabled != 0)



#ifndef ARCH_HAS_NOCACHE_UACCESS



static inline unsigned long __copy_from_user_inatomic_nocache(void *to,

kernel/fork.c

+3 −0
Original line number Diff line number Diff line
@@ -1393,6 +1393,9 @@ static struct task_struct *copy_process(unsigned long clone_flags, 
	p->hardirq_context = 0;

	p->softirq_context = 0;

#endif



	p->pagefault_disabled = 0;



#ifdef CONFIG_LOCKDEP

	p->lockdep_depth = 0; /* no locks held yet */

	p->curr_chain_key = 0;