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>

diff --git a/arch/s390/include/asm/processor.h b/arch/s390/include/asm/processor.h
index b16c3d0a1b9fc180bee2846ba5e057bd6cd40983..5592c94ebe3109242bf9542fa32075a5fe3c2ee0 100644 (file)
--- 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 857b6526d29833507c3abec126b90a24e491956f..cd5a191381b9438c2314294c350367ce9cabd062 100644 (file)
--- 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 0a68fe04a9e16d585a9e7b7af6325420f9295799..d4549c9645892aef684c60ac73a2c8d22886e58e 100644 (file)
--- 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);
 }