Commit 6a942f57 authored by Valentin Schneider's avatar Valentin Schneider Committed by Vasily Gorbik
Browse files

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: f1a0a376 ("sched/core: Initialize the idle task with preemption disabled")
Reported-by: default avatarGuenter Roeck <linux@roeck-us.net>
Signed-off-by: default avatarValentin Schneider <valentin.schneider@arm.com>
Tested-by: default avatarGuenter Roeck <linux@roeck-us.net>
Reviewed-by: default avatarHeiko Carstens <hca@linux.ibm.com>
Link: https://lore.kernel.org/r/20210707163338.1623014-1-valentin.schneider@arm.com


Signed-off-by: default avatarVasily Gorbik <gor@linux.ibm.com>
parent 4ee471fe

arch/s390/include/asm/preempt.h

+4 −12
Original line number Diff line number Diff line
@@ -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()

arch/s390/kernel/setup.c

+1 −0
Original line number Diff line number Diff line
@@ -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;

arch/s390/kernel/smp.c

+1 −0
Original line number Diff line number Diff line
@@ -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;