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authorMartin Schwidefsky <schwidefsky@de.ibm.com>2015-11-19 11:09:45 +0100
committerMartin Schwidefsky <schwidefsky@de.ibm.com>2015-11-27 09:24:18 +0100
commit419123f900dac58fb27ce5285b21074f5300095a (patch)
treed0b0d72691d4e2e3df0e9f4d2e335bebc378fdeb /arch
parentc6f70d3b8a32fdec60d3f78cb59423f056f16688 (diff)
downloadlinux-419123f900dac58fb27ce5285b21074f5300095a.tar.bz2
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: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Diffstat (limited to 'arch')
-rw-r--r--arch/s390/include/asm/processor.h12
-rw-r--r--arch/s390/kernel/entry.S2
-rw-r--r--arch/s390/lib/spinlock.c25
3 files changed, 31 insertions, 8 deletions
diff --git a/arch/s390/include/asm/processor.h b/arch/s390/include/asm/processor.h
index b16c3d0a1b9f..5592c94ebe31 100644
--- a/arch/s390/include/asm/processor.h
+++ b/arch/s390/include/asm/processor.h
@@ -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)
/*
diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
index 857b6526d298..cd5a191381b9 100644
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -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
diff --git a/arch/s390/lib/spinlock.c b/arch/s390/lib/spinlock.c
index 0a68fe04a9e1..d4549c964589 100644
--- a/arch/s390/lib/spinlock.c
+++ b/arch/s390/lib/spinlock.c
@@ -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);
}