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Commit c55f5158 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched, mips, ia64: Remove __ARCH_WANT_UNLOCKED_CTXSW 



Kirill found that there's a subtle race in the
__ARCH_WANT_UNLOCKED_CTXSW code, and instead of fixing it, remove the
entire exception because neither arch that uses it seems to actually
still require it.

Boot tested on mips64el (qemu) only.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarKirill Tkhai <tkhai@yandex.ru>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Davidlohr Bueso <davidlohr@hp.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: Qais Yousef <qais.yousef@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: oleg@redhat.com
Cc: linux@roeck-us.net
Cc: linux-ia64@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Link: http://lkml.kernel.org/r/20140923150641.GH3312@worktop.programming.kicks-ass.net


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 5bd96ab6

arch/ia64/include/asm/processor.h

+0 −1
Original line number Diff line number Diff line
@@ -19,7 +19,6 @@ 
#include <asm/ptrace.h>

#include <asm/ustack.h>



#define __ARCH_WANT_UNLOCKED_CTXSW

#define ARCH_HAS_PREFETCH_SWITCH_STACK



#define IA64_NUM_PHYS_STACK_REG	96

arch/mips/include/asm/processor.h

+0 −6
Original line number Diff line number Diff line
@@ -397,12 +397,6 @@ unsigned long get_wchan(struct task_struct *p); 
#define ARCH_HAS_PREFETCHW

#define prefetchw(x) __builtin_prefetch((x), 1, 1)



/*

 * See Documentation/scheduler/sched-arch.txt; prevents deadlock on SMP

 * systems.

 */

#define __ARCH_WANT_UNLOCKED_CTXSW



#endif



#endif /* _ASM_PROCESSOR_H */

kernel/sched/core.c

+0 −6
Original line number Diff line number Diff line
@@ -2331,10 +2331,6 @@ asmlinkage __visible void schedule_tail(struct task_struct *prev) 
	 */

	post_schedule(rq);



#ifdef __ARCH_WANT_UNLOCKED_CTXSW

	/* In this case, finish_task_switch does not reenable preemption */

	preempt_enable();

#endif

	if (current->set_child_tid)

		put_user(task_pid_vnr(current), current->set_child_tid);

}
@@ -2377,9 +2373,7 @@ context_switch(struct rq *rq, struct task_struct *prev, 
	 * of the scheduler it's an obvious special-case), so we

	 * do an early lockdep release here:

	 */

#ifndef __ARCH_WANT_UNLOCKED_CTXSW

	spin_release(&rq->lock.dep_map, 1, _THIS_IP_);

#endif



	context_tracking_task_switch(prev, next);

	/* Here we just switch the register state and the stack. */

kernel/sched/sched.h

+0 −30
Original line number Diff line number Diff line
@@ -975,7 +975,6 @@ static inline int task_on_rq_migrating(struct task_struct *p) 
# define finish_arch_post_lock_switch()	do { } while (0)

#endif



#ifndef __ARCH_WANT_UNLOCKED_CTXSW

static inline void prepare_lock_switch(struct rq *rq, struct task_struct *next)

{

#ifdef CONFIG_SMP
@@ -1013,35 +1012,6 @@ static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev) 
	raw_spin_unlock_irq(&rq->lock);

}



#else /* __ARCH_WANT_UNLOCKED_CTXSW */

static inline void prepare_lock_switch(struct rq *rq, struct task_struct *next)

{

#ifdef CONFIG_SMP

	/*

	 * We can optimise this out completely for !SMP, because the

	 * SMP rebalancing from interrupt is the only thing that cares

	 * here.

	 */

	next->on_cpu = 1;

#endif

	raw_spin_unlock(&rq->lock);

}



static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev)

{

#ifdef CONFIG_SMP

	/*

	 * After ->on_cpu is cleared, the task can be moved to a different CPU.

	 * We must ensure this doesn't happen until the switch is completely

	 * finished.

	 */

	smp_wmb();

	prev->on_cpu = 0;

#endif

	local_irq_enable();

}

#endif /* __ARCH_WANT_UNLOCKED_CTXSW */



/*

 * wake flags

 */