1 files changed, 22 insertions, 31 deletions

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index e9eaec522655..668f66baac7b 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -22,7 +22,7 @@ extern int cpuset_init(void);
 extern void cpuset_init_smp(void);
 extern void cpuset_update_active_cpus(void);
 extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
-extern int cpuset_cpus_allowed_fallback(struct task_struct *p);
+extern void cpuset_cpus_allowed_fallback(struct task_struct *p);
 extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
 #define cpuset_current_mems_allowed (current->mems_allowed)
 void cpuset_init_current_mems_allowed(void);
@@ -89,42 +89,33 @@ extern void rebuild_sched_domains(void);
 extern void cpuset_print_task_mems_allowed(struct task_struct *p);
 
 /*
- * reading current mems_allowed and mempolicy in the fastpath must protected
- * by get_mems_allowed()
+ * get_mems_allowed is required when making decisions involving mems_allowed
+ * such as during page allocation. mems_allowed can be updated in parallel
+ * and depending on the new value an operation can fail potentially causing
+ * process failure. A retry loop with get_mems_allowed and put_mems_allowed
+ * prevents these artificial failures.
  */
-static inline void get_mems_allowed(void)
+static inline unsigned int get_mems_allowed(void)
 {
-        current->mems_allowed_change_disable++;
-
-        /*
-         * ensure that reading mems_allowed and mempolicy happens after the
-         * update of ->mems_allowed_change_disable.
-         *
-         * the write-side task finds ->mems_allowed_change_disable is not 0,
-         * and knows the read-side task is reading mems_allowed or mempolicy,
-         * so it will clear old bits lazily.
-         */
-        smp_mb();
+        return read_seqcount_begin(&current->mems_allowed_seq);
 }
 
-static inline void put_mems_allowed(void)
+/*
+ * If this returns false, the operation that took place after get_mems_allowed
+ * may have failed. It is up to the caller to retry the operation if
+ * appropriate.
+ */
+static inline bool put_mems_allowed(unsigned int seq)
 {
-        /*
-         * ensure that reading mems_allowed and mempolicy before reducing
-         * mems_allowed_change_disable.
-         *
-         * the write-side task will know that the read-side task is still
-         * reading mems_allowed or mempolicy, don't clears old bits in the
-         * nodemask.
-         */
-        smp_mb();
-        --ACCESS_ONCE(current->mems_allowed_change_disable);
+        return !read_seqcount_retry(&current->mems_allowed_seq, seq);
 }
 
 static inline void set_mems_allowed(nodemask_t nodemask)
 {
         task_lock(current);
+        write_seqcount_begin(&current->mems_allowed_seq);
         current->mems_allowed = nodemask;
+        write_seqcount_end(&current->mems_allowed_seq);
         task_unlock(current);
 }
 
@@ -144,10 +135,8 @@ static inline void cpuset_cpus_allowed(struct task_struct *p,
         cpumask_copy(mask, cpu_possible_mask);
 }
 
-static inline int cpuset_cpus_allowed_fallback(struct task_struct *p)
+static inline void cpuset_cpus_allowed_fallback(struct task_struct *p)
 {
-        do_set_cpus_allowed(p, cpu_possible_mask);
-        return cpumask_any(cpu_active_mask);
 }
 
 static inline nodemask_t cpuset_mems_allowed(struct task_struct *p)
@@ -234,12 +223,14 @@ static inline void set_mems_allowed(nodemask_t nodemask)
 {
 }
 
-static inline void get_mems_allowed(void)
+static inline unsigned int get_mems_allowed(void)
 {
+        return 0;
 }
 
-static inline void put_mems_allowed(void)
+static inline bool put_mems_allowed(unsigned int seq)
 {
+        return true;
 }
 
 #endif /* !CONFIG_CPUSETS */