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

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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: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Martin Schwidefsky 2015-11-19 11:09:45 +01:00
parent c6f70d3b8a
commit 419123f900
3 changed files with 31 additions and 8 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

12
arch/s390/include/asm/processor.h
View file

@ -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)
/*

2
arch/s390/kernel/entry.S
View file

@ -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

25
arch/s390/lib/spinlock.c
View file

@ -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);
}