From 6a942f5780545ebd11aca8b3ac4b163397962322 Mon Sep 17 00:00:00 2001 From: Valentin Schneider Date: Wed, 7 Jul 2021 17:33:38 +0100 Subject: [PATCH] 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: f1a0a376ca0c ("sched/core: Initialize the idle task with preemption disabled") Reported-by: Guenter Roeck Signed-off-by: Valentin Schneider Tested-by: Guenter Roeck Reviewed-by: Heiko Carstens Link: https://lore.kernel.org/r/20210707163338.1623014-1-valentin.schneider@arm.com Signed-off-by: Vasily Gorbik --- arch/s390/include/asm/preempt.h | 16 ++++------------ arch/s390/kernel/setup.c | 1 + arch/s390/kernel/smp.c | 1 + 3 files changed, 6 insertions(+), 12 deletions(-) diff --git a/arch/s390/include/asm/preempt.h b/arch/s390/include/asm/preempt.h index 23ff51be7e29..d9d5350cc3ec 100644 --- a/arch/s390/include/asm/preempt.h +++ b/arch/s390/include/asm/preempt.h @@ -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() diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c index d55c636e4889..9e1f538e58e6 100644 --- a/arch/s390/kernel/setup.c +++ b/arch/s390/kernel/setup.c @@ -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; diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c index a0a8c0abf7de..8984711f72ed 100644 --- a/arch/s390/kernel/smp.c +++ b/arch/s390/kernel/smp.c @@ -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; -- 2.11.0