Commit 419123f9 authored by Martin Schwidefsky's avatar Martin Schwidefsky
Browse files

s390/spinlock: do not yield to a CPU in udelay/mdelay 



It does not make sense to try to relinquish the time slice with diag 0x9c
to a CPU in a state that does not allow to schedule the CPU. The scenario
where this can happen is a CPU waiting in udelay/mdelay while holding a
spin-lock.

Add a CIF bit to tag a CPU in enabled wait and use it to detect that the
yield of a CPU will not be successful and skip the diagnose call.

Reviewed-by: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent c6f70d3b

arch/s390/include/asm/processor.h

+12 −0
Original line number Diff line number Diff line
@@ -18,12 +18,14 @@ 
#define CIF_NOHZ_DELAY		2	/* delay HZ disable for a tick */

#define CIF_FPU			3	/* restore FPU registers */

#define CIF_IGNORE_IRQ		4	/* ignore interrupt (for udelay) */

#define CIF_ENABLED_WAIT	5	/* in enabled wait state */



#define _CIF_MCCK_PENDING	_BITUL(CIF_MCCK_PENDING)

#define _CIF_ASCE		_BITUL(CIF_ASCE)

#define _CIF_NOHZ_DELAY		_BITUL(CIF_NOHZ_DELAY)

#define _CIF_FPU		_BITUL(CIF_FPU)

#define _CIF_IGNORE_IRQ		_BITUL(CIF_IGNORE_IRQ)

#define _CIF_ENABLED_WAIT	_BITUL(CIF_ENABLED_WAIT)



#ifndef __ASSEMBLY__
@@ -52,6 +54,16 @@ static inline int test_cpu_flag(int flag) 
	return !!(S390_lowcore.cpu_flags & (1UL << flag));

}



/*

 * Test CIF flag of another CPU. The caller needs to ensure that

 * CPU hotplug can not happen, e.g. by disabling preemption.

 */

static inline int test_cpu_flag_of(int flag, int cpu)

{

	struct _lowcore *lc = lowcore_ptr[cpu];

	return !!(lc->cpu_flags & (1UL << flag));

}



#define arch_needs_cpu() test_cpu_flag(CIF_NOHZ_DELAY)



/*

arch/s390/kernel/entry.S

+2 −0
Original line number Diff line number Diff line
@@ -764,6 +764,7 @@ ENTRY(psw_idle) 
	.insn	rsy,0xeb0000000017,%r1,5,__SF_EMPTY+16(%r15)

.Lpsw_idle_stcctm:

#endif

	oi	__LC_CPU_FLAGS+7,_CIF_ENABLED_WAIT

	STCK	__CLOCK_IDLE_ENTER(%r2)

	stpt	__TIMER_IDLE_ENTER(%r2)

.Lpsw_idle_lpsw:
@@ -1146,6 +1147,7 @@ cleanup_critical: 
	.quad	.Lio_done - 4



.Lcleanup_idle:

	ni	__LC_CPU_FLAGS+7,255-_CIF_ENABLED_WAIT

	# copy interrupt clock & cpu timer

	mvc	__CLOCK_IDLE_EXIT(8,%r2),__LC_INT_CLOCK

	mvc	__TIMER_IDLE_EXIT(8,%r2),__LC_ASYNC_ENTER_TIMER

arch/s390/lib/spinlock.c

+17 −8
Original line number Diff line number Diff line
@@ -37,6 +37,15 @@ static inline void _raw_compare_and_delay(unsigned int *lock, unsigned int old) 
	asm(".insn rsy,0xeb0000000022,%0,0,%1" : : "d" (old), "Q" (*lock));

}



static inline int cpu_is_preempted(int cpu)

{

	if (test_cpu_flag_of(CIF_ENABLED_WAIT, cpu))

		return 0;

	if (smp_vcpu_scheduled(cpu))

		return 0;

	return 1;

}



void arch_spin_lock_wait(arch_spinlock_t *lp)

{

	unsigned int cpu = SPINLOCK_LOCKVAL;
@@ -53,7 +62,7 @@ void arch_spin_lock_wait(arch_spinlock_t *lp) 
			continue;

		}

		/* First iteration: check if the lock owner is running. */

		if (first_diag && !smp_vcpu_scheduled(~owner)) {

		if (first_diag && cpu_is_preempted(~owner)) {

			smp_yield_cpu(~owner);

			first_diag = 0;

			continue;
@@ -72,7 +81,7 @@ void arch_spin_lock_wait(arch_spinlock_t *lp) 
		 * yield the CPU unconditionally. For LPAR rely on the

		 * sense running status.

		 */

		if (!MACHINE_IS_LPAR || !smp_vcpu_scheduled(~owner)) {

		if (!MACHINE_IS_LPAR || cpu_is_preempted(~owner)) {

			smp_yield_cpu(~owner);

			first_diag = 0;

		}
@@ -98,7 +107,7 @@ void arch_spin_lock_wait_flags(arch_spinlock_t *lp, unsigned long flags) 
			local_irq_restore(flags);

		}

		/* Check if the lock owner is running. */

		if (first_diag && !smp_vcpu_scheduled(~owner)) {

		if (first_diag && cpu_is_preempted(~owner)) {

			smp_yield_cpu(~owner);

			first_diag = 0;

			continue;
@@ -117,7 +126,7 @@ void arch_spin_lock_wait_flags(arch_spinlock_t *lp, unsigned long flags) 
		 * yield the CPU unconditionally. For LPAR rely on the

		 * sense running status.

		 */

		if (!MACHINE_IS_LPAR || !smp_vcpu_scheduled(~owner)) {

		if (!MACHINE_IS_LPAR || cpu_is_preempted(~owner)) {

			smp_yield_cpu(~owner);

			first_diag = 0;

		}
@@ -155,7 +164,7 @@ void _raw_read_lock_wait(arch_rwlock_t *rw) 
	owner = 0;

	while (1) {

		if (count-- <= 0) {

			if (owner && !smp_vcpu_scheduled(~owner))

			if (owner && cpu_is_preempted(~owner))

				smp_yield_cpu(~owner);

			count = spin_retry;

		}
@@ -201,7 +210,7 @@ void _raw_write_lock_wait(arch_rwlock_t *rw, unsigned int prev) 
	owner = 0;

	while (1) {

		if (count-- <= 0) {

			if (owner && !smp_vcpu_scheduled(~owner))

			if (owner && cpu_is_preempted(~owner))

				smp_yield_cpu(~owner);

			count = spin_retry;

		}
@@ -231,7 +240,7 @@ void _raw_write_lock_wait(arch_rwlock_t *rw) 
	owner = 0;

	while (1) {

		if (count-- <= 0) {

			if (owner && !smp_vcpu_scheduled(~owner))

			if (owner && cpu_is_preempted(~owner))

				smp_yield_cpu(~owner);

			count = spin_retry;

		}
@@ -275,7 +284,7 @@ void arch_lock_relax(unsigned int cpu) 
{

	if (!cpu)

		return;

	if (MACHINE_IS_LPAR && smp_vcpu_scheduled(~cpu))

	if (MACHINE_IS_LPAR && !cpu_is_preempted(~cpu))

		return;

	smp_yield_cpu(~cpu);

}

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