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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>
This commit is contained in:
Valentin Schneider 2021-07-07 17:33:38 +01:00 committed by Vasily Gorbik
parent 4ee471fe5a
commit 6a942f5780
3 changed files with 6 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
arch/s390/include/asm/preempt.h
View File

@ -29,12 +29,6 @@ static inline void preempt_count_set(int pc)
old, new) != old);
}
#define init_task_preempt_count(p) do { } while (0)
#define init_idle_preempt_count(p, cpu) do { \
S390_lowcore.preempt_count = PREEMPT_DISABLED; \
} while (0)
static inline void set_preempt_need_resched(void)
{
__atomic_and(~PREEMPT_NEED_RESCHED, &S390_lowcore.preempt_count);
@ -88,12 +82,6 @@ static inline void preempt_count_set(int pc)
S390_lowcore.preempt_count = pc;
}
#define init_task_preempt_count(p) do { } while (0)
#define init_idle_preempt_count(p, cpu) do { \
S390_lowcore.preempt_count = PREEMPT_DISABLED; \
} while (0)
static inline void set_preempt_need_resched(void)
{
}
@ -130,6 +118,10 @@ static inline bool should_resched(int preempt_offset)
#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()

1
arch/s390/kernel/setup.c
View File

@ -442,6 +442,7 @@ static void __init setup_lowcore_dat_off(void)
lc->br_r1_trampoline = 0x07f1; /* br %r1 */
lc->return_lpswe = gen_lpswe(__LC_RETURN_PSW);
lc->return_mcck_lpswe = gen_lpswe(__LC_RETURN_MCCK_PSW);
lc->preempt_count = PREEMPT_DISABLED;
set_prefix((u32)(unsigned long) lc);
lowcore_ptr[0] = lc;

1
arch/s390/kernel/smp.c
View File

@ -210,6 +210,7 @@ static int pcpu_alloc_lowcore(struct pcpu *pcpu, int cpu)
lc->br_r1_trampoline = 0x07f1; /* br %r1 */
lc->return_lpswe = gen_lpswe(__LC_RETURN_PSW);
lc->return_mcck_lpswe = gen_lpswe(__LC_RETURN_MCCK_PSW);
lc->preempt_count = PREEMPT_DISABLED;
if (nmi_alloc_per_cpu(lc))
goto out;
lowcore_ptr[cpu] = lc;