cpuset: PF_SPREAD_PAGE and PF_SPREAD_SLAB should be atomic flags

[pandora-kernel.git] / include / linux / cpuset.h

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index e9eaec5..1dc9427 100644 (file)
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -74,12 +74,12 @@ extern int cpuset_slab_spread_node(void);
 
 static inline int cpuset_do_page_mem_spread(void)
 {
-       return current->flags & PF_SPREAD_PAGE;
+       return task_spread_page(current);
 }
 
 static inline int cpuset_do_slab_mem_spread(void)
 {
-       return current->flags & PF_SPREAD_SLAB;
+       return task_spread_slab(current);
 }
 
 extern int current_cpuset_is_being_rebound(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);
 }
 
@@ -234,12 +225,14 @@ 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 */