cpumask: add cpumask_var_t documentation

cpumask_var_t has one notable difference from cpumask_t. Add the explanation. Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Thiago Farina <tfransosi@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

cpumask: add cpumask_var_t documentation
cpumask_var_t has one notable difference from cpumask_t. Add the explanation. Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Thiago Farina <tfransosi@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
KOSAKI Motohiro · Linus Torvalds
1 parent 37e7b5f153
Showing 1 changed file with 14 additions and 0 deletions Side-by-side Diff
include/linux/cpumask.h
@@ -617,6 +617,20 @@
  *	  ... use 'tmpmask' like a normal struct cpumask * ...
  *
  *	free_cpumask_var(tmpmask);
+ *
+ *
+ * However, one notable exception is there. alloc_cpumask_var() allocates
+ * only nr_cpumask_bits bits (in the other hand, real cpumask_t always has
+ * NR_CPUS bits). Therefore you don't have to dereference cpumask_var_t.
+ *
+ *	cpumask_var_t tmpmask;
+ *	if (!alloc_cpumask_var(&tmpmask, GFP_KERNEL))
+ *		return -ENOMEM;
+ *
+ *	var = *tmpmask;
+ *
+ * This code makes NR_CPUS length memcopy and brings to a memory corruption.
+ * cpumask_copy() provide safe copy functionality.
  */
 #ifdef CONFIG_CPUMASK_OFFSTACK
 typedef struct cpumask *cpumask_var_t;
...	...	@@ -617,6 +617,20 @@
617	617	* ... use 'tmpmask' like a normal struct cpumask * ...
618	618	*
619	619	* free_cpumask_var(tmpmask);
	620	+ *
	621	+ *
	622	+ * However, one notable exception is there. alloc_cpumask_var() allocates
	623	+ * only nr_cpumask_bits bits (in the other hand, real cpumask_t always has
	624	+ * NR_CPUS bits). Therefore you don't have to dereference cpumask_var_t.
	625	+ *
	626	+ * cpumask_var_t tmpmask;
	627	+ * if (!alloc_cpumask_var(&tmpmask, GFP_KERNEL))
	628	+ * return -ENOMEM;
	629	+ *
	630	+ * var = *tmpmask;
	631	+ *
	632	+ * This code makes NR_CPUS length memcopy and brings to a memory corruption.
	633	+ * cpumask_copy() provide safe copy functionality.
620	634	*/
621	635	#ifdef CONFIG_CPUMASK_OFFSTACK
622	636	typedef struct cpumask *cpumask_var_t;