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authorKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>2011-07-26 16:08:45 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-07-26 16:49:44 -0700
commita64a26e822ddb739de464540dfd2cbb6abce47d5 (patch)
tree95d8e783342d64c2c63d98ec5814b4405cab7370
parent37e7b5f1535dddaace865b25df34a2d049a3a66f (diff)
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>
-rw-r--r--include/linux/cpumask.h14
1 files changed, 14 insertions, 0 deletions
diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index b24ac56477b4..4f7a63237471 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -617,6 +617,20 @@ static inline size_t cpumask_size(void)
* ... 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;

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