sched,arm64: Handle CPU isolation on last resort fallback rq selection

When a kthread or any other task has an affinity mask that is fully
offline or unallowed, the scheduler reaffines the task to all possible
CPUs as a last resort.

This default decision doesn't mix up very well with nohz_full CPUs that
are part of the possible cpumask but don't want to be disturbed by
unbound kthreads or even detached pinned user tasks.

Make the fallback affinity setting aware of nohz_full.

Suggested-by: Michal Hocko <mhocko@suse.com>
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 8b4e5a3..cac5efc 100644 (file)
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -671,6 +671,7 @@ static inline bool supports_clearbhb(int scope)
 }
 
 const struct cpumask *system_32bit_el0_cpumask(void);
+const struct cpumask *fallback_32bit_el0_cpumask(void);
 DECLARE_STATIC_KEY_FALSE(arm64_mismatched_32bit_el0);
 
 static inline bool system_supports_32bit_el0(void)

diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h
index 48b3d95..0dbe3b2 100644 (file)
--- a/arch/arm64/include/asm/mmu_context.h
+++ b/arch/arm64/include/asm/mmu_context.h
@@ -271,18 +271,26 @@ switch_mm(struct mm_struct *prev, struct mm_struct *next,
 }
 
 static inline const struct cpumask *
-task_cpu_possible_mask(struct task_struct *p)
+__task_cpu_possible_mask(struct task_struct *p, const struct cpumask *mask)
 {
        if (!static_branch_unlikely(&arm64_mismatched_32bit_el0))
-               return cpu_possible_mask;
+               return mask;
 
        if (!is_compat_thread(task_thread_info(p)))
-               return cpu_possible_mask;
+               return mask;
 
        return system_32bit_el0_cpumask();
 }
+
+static inline const struct cpumask *
+task_cpu_possible_mask(struct task_struct *p)
+{
+       return __task_cpu_possible_mask(p, cpu_possible_mask);
+}
 #define task_cpu_possible_mask task_cpu_possible_mask
 
+const struct cpumask *task_cpu_fallback_mask(struct task_struct *p);
+
 void verify_cpu_asid_bits(void);
 void post_ttbr_update_workaround(void);
 

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 3c87659..a983e86 100644 (file)
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1642,6 +1642,11 @@ const struct cpumask *system_32bit_el0_cpumask(void)
        return cpu_possible_mask;
 }
 
+const struct cpumask *task_cpu_fallback_mask(struct task_struct *p)
+{
+       return __task_cpu_possible_mask(p, housekeeping_cpumask(HK_TYPE_TICK));
+}
+
 static int __init parse_32bit_el0_param(char *str)
 {
        allow_mismatched_32bit_el0 = true;

diff --git a/include/linux/mmu_context.h b/include/linux/mmu_context.h
index bbaec80..ac01dc4 100644 (file)
--- a/include/linux/mmu_context.h
+++ b/include/linux/mmu_context.h
@@ -24,6 +24,7 @@ static inline void leave_mm(void) { }
 #ifndef task_cpu_possible_mask
 # define task_cpu_possible_mask(p)     cpu_possible_mask
 # define task_cpu_possible(cpu, p)     true
+# define task_cpu_fallback_mask(p)     housekeeping_cpumask(HK_TYPE_TICK)
 #else
 # define task_cpu_possible(cpu, p)     cpumask_test_cpu((cpu), task_cpu_possible_mask(p))
 #endif

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 95e4089..233b50b 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3534,7 +3534,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
                         *
                         * More yuck to audit.
                         */
-                       do_set_cpus_allowed(p, task_cpu_possible_mask(p));
+                       do_set_cpus_allowed(p, task_cpu_fallback_mask(p));
                        state = fail;
                        break;
                case fail: