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linux/arch/s390/include/asm/preempt.h
Valentin Schneider 6a942f5780 s390: preempt: Fix preempt_count initialization
S390's init_idle_preempt_count(p, cpu) doesn't actually let us initialize the
preempt_count of the requested CPU's idle task: it unconditionally writes
to the current CPU's. This clearly conflicts with idle_threads_init(),
which intends to initialize *all* the idle tasks, including their
preempt_count (or their CPU's, if the arch uses a per-CPU preempt_count).

Unfortunately, it seems the way s390 does things doesn't let us initialize
every possible CPU's preempt_count early on, as the pages where this
resides are only allocated when a CPU is brought up and are freed when it
is brought down.

Let the arch-specific code set a CPU's preempt_count when its lowcore is
allocated, and turn init_idle_preempt_count() into an empty stub.

Fixes: f1a0a376ca ("sched/core: Initialize the idle task with preemption disabled")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Link: https://lore.kernel.org/r/20210707163338.1623014-1-valentin.schneider@arm.com
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
2021-07-08 22:12:18 +02:00

133 lines
2.9 KiB
C

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __ASM_PREEMPT_H
#define __ASM_PREEMPT_H
#include <asm/current.h>
#include <linux/thread_info.h>
#include <asm/atomic_ops.h>
#ifdef CONFIG_HAVE_MARCH_Z196_FEATURES
/* We use the MSB mostly because its available */
#define PREEMPT_NEED_RESCHED 0x80000000
#define PREEMPT_ENABLED (0 + PREEMPT_NEED_RESCHED)
static inline int preempt_count(void)
{
return READ_ONCE(S390_lowcore.preempt_count) & ~PREEMPT_NEED_RESCHED;
}
static inline void preempt_count_set(int pc)
{
int old, new;
do {
old = READ_ONCE(S390_lowcore.preempt_count);
new = (old & PREEMPT_NEED_RESCHED) |
(pc & ~PREEMPT_NEED_RESCHED);
} while (__atomic_cmpxchg(&S390_lowcore.preempt_count,
old, new) != old);
}
static inline void set_preempt_need_resched(void)
{
__atomic_and(~PREEMPT_NEED_RESCHED, &S390_lowcore.preempt_count);
}
static inline void clear_preempt_need_resched(void)
{
__atomic_or(PREEMPT_NEED_RESCHED, &S390_lowcore.preempt_count);
}
static inline bool test_preempt_need_resched(void)
{
return !(READ_ONCE(S390_lowcore.preempt_count) & PREEMPT_NEED_RESCHED);
}
static inline void __preempt_count_add(int val)
{
if (__builtin_constant_p(val) && (val >= -128) && (val <= 127))
__atomic_add_const(val, &S390_lowcore.preempt_count);
else
__atomic_add(val, &S390_lowcore.preempt_count);
}
static inline void __preempt_count_sub(int val)
{
__preempt_count_add(-val);
}
static inline bool __preempt_count_dec_and_test(void)
{
return __atomic_add(-1, &S390_lowcore.preempt_count) == 1;
}
static inline bool should_resched(int preempt_offset)
{
return unlikely(READ_ONCE(S390_lowcore.preempt_count) ==
preempt_offset);
}
#else /* CONFIG_HAVE_MARCH_Z196_FEATURES */
#define PREEMPT_ENABLED (0)
static inline int preempt_count(void)
{
return READ_ONCE(S390_lowcore.preempt_count);
}
static inline void preempt_count_set(int pc)
{
S390_lowcore.preempt_count = pc;
}
static inline void set_preempt_need_resched(void)
{
}
static inline void clear_preempt_need_resched(void)
{
}
static inline bool test_preempt_need_resched(void)
{
return false;
}
static inline void __preempt_count_add(int val)
{
S390_lowcore.preempt_count += val;
}
static inline void __preempt_count_sub(int val)
{
S390_lowcore.preempt_count -= val;
}
static inline bool __preempt_count_dec_and_test(void)
{
return !--S390_lowcore.preempt_count && tif_need_resched();
}
static inline bool should_resched(int preempt_offset)
{
return unlikely(preempt_count() == preempt_offset &&
tif_need_resched());
}
#endif /* CONFIG_HAVE_MARCH_Z196_FEATURES */
#define init_task_preempt_count(p) do { } while (0)
/* Deferred to CPU bringup time */
#define init_idle_preempt_count(p, cpu) do { } while (0)
#ifdef CONFIG_PREEMPTION
extern void preempt_schedule(void);
#define __preempt_schedule() preempt_schedule()
extern void preempt_schedule_notrace(void);
#define __preempt_schedule_notrace() preempt_schedule_notrace()
#endif /* CONFIG_PREEMPTION */
#endif /* __ASM_PREEMPT_H */