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(¤t->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(¤t->mems_allowed_seq, seq);
}
static inline void set_mems_allowed(nodemask_t nodemask)
{
task_lock(current);
+ write_seqcount_begin(¤t->mems_allowed_seq);
current->mems_allowed = nodemask;
+ write_seqcount_end(¤t->mems_allowed_seq);
task_unlock(current);
}
{
}
-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 */