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authorValentin Schneider <valentin.schneider@arm.com>2021-07-07 19:33:38 +0300
committerVasily Gorbik <gor@linux.ibm.com>2021-07-08 23:12:18 +0300
commit6a942f5780545ebd11aca8b3ac4b163397962322 (patch)
treef0a20802aa79e32712f4b3ca893166a3072ab98b
parent4ee471fe5a5a891ac4fcd45b5457fcb17de694de (diff)
downloadlinux-6a942f5780545ebd11aca8b3ac4b163397962322.tar.xz
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 <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>
-rw-r--r--arch/s390/include/asm/preempt.h16
-rw-r--r--arch/s390/kernel/setup.c1
-rw-r--r--arch/s390/kernel/smp.c1
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;