Patch "cpumask: use nr_cpumask_bits for parsing functions" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

cpumask: use nr_cpumask_bits for parsing functions

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
cpumask-use-nr_cpumask_bits-for-parsing-functions.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Tejun Heo <[email protected]>
Date: Wed, 8 Feb 2017 14:30:56 -0800
Subject: cpumask: use nr_cpumask_bits for parsing functions

From: Tejun Heo <[email protected]>

commit 4d59b6ccf000862beed6fc0765d3209f98a8d8a2 upstream.

Commit 513e3d2d11c9 ("cpumask: always use nr_cpu_ids in formatting and parsing functions") converted both cpumask printing and parsing functions to use nr_cpu_ids instead of nr_cpumask_bits. While this was okay for the printing functions as it just picked one of the two output formats that we were alternating between depending on a kernel config, doing the same for parsing wasn't okay.

nr_cpumask_bits can be either nr_cpu_ids or NR_CPUS. We can always use nr_cpu_ids but that is a variable while NR_CPUS is a constant, so it can be more efficient to use NR_CPUS when we can get away with it. Converting the printing functions to nr_cpu_ids makes sense because it affects how the masks get presented to userspace and doesn't break anything; however, using nr_cpu_ids for parsing functions can incorrectly leave the higher bits uninitialized while reading in these masks from userland. As all testing and comparison functions use nr_cpumask_bits which can be larger than nr_cpu_ids, the parsed cpumasks can erroneously yield false negative results.

This made the taskstats interface incorrectly return -EINVAL even when the inputs were correct.

Fix it by restoring the parse functions to use nr_cpumask_bits instead of nr_cpu_ids.

---
 include/linux/cpumask.h |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

@@ -556,7 +556,7 @@ static inline void cpumask_copy(struct c
 static inline int cpumask_parse_user(const char __user *buf, int len,
 				     struct cpumask *dstp)
 {
-	return bitmap_parse_user(buf, len, cpumask_bits(dstp), nr_cpu_ids);
+	return bitmap_parse_user(buf, len, cpumask_bits(dstp), nr_cpumask_bits);
 }
 
 /**

@@ -571,7 +571,7 @@ static inline int cpumask_parselist_user
 				     struct cpumask *dstp)
 {
 	return bitmap_parselist_user(buf, len, cpumask_bits(dstp),
-				     nr_cpu_ids);
+				     nr_cpumask_bits);
 }
 
 /**

@@ -586,7 +586,7 @@ static inline int cpumask_parse(const ch
 	char *nl = strchr(buf, '\n');
 	unsigned int len = nl ? (unsigned int)(nl - buf) : strlen(buf);
 
-	return bitmap_parse(buf, len, cpumask_bits(dstp), nr_cpu_ids);
+	return bitmap_parse(buf, len, cpumask_bits(dstp), nr_cpumask_bits);
 }
 
 /**

@@ -598,7 +598,7 @@ static inline int cpumask_parse(const ch
  */
 static inline int cpulist_parse(const char *buf, struct cpumask *dstp)
 {
-	return bitmap_parselist(buf, cpumask_bits(dstp), nr_cpu_ids);
+	return bitmap_parselist(buf, cpumask_bits(dstp), nr_cpumask_bits);
 }
 
 /**

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/cpumask-use-nr_cpumask_bits-for-parsing-functions.patch