linux-kernel - [PATCH] cpumask: use nr_cpumask

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Date:   Mon, 6 Feb 2017 13:24:42 -0500
From:   Tejun Heo <tj@...nel.org>
To:     Martin Steigerwald <martin.steigerwald@...mix.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, Andrew Morton <akpm@...l.org>,
        Ingo Molnar <mingo@...e.hu>,
        LKML <linux-kernel@...r.kernel.org>,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        Jay Lan <jlan@...r.sgi.com>,
        Martin Steigerwald <martin@...htvoll.de>,
        Gerlof Langeveld <gerlof.langeveld@...ptool.nl>,
        Marc Haber <mh+debian-packages@...schlus.de>,
        Ben Hutchings <ben@...adent.org.uk>,
        Balbir Singh <bsingharora@...il.com>, kernel-team@...com
Subject: [PATCH] cpumask: use nr_cpumask_bits for parsing functions

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.

Signed-off-by: Tejun Heo <tj@...nel.org>
Fixes: 513e3d2d11c9 ("cpumask: always use nr_cpu_ids in formatting and parsing functions")
Cc: stable@...r.kernel.org # v4.0+
Reported-by: Martin Steigerwald <martin.steigerwald@...mix.de>
Debugged-by: Ben Hutchings <ben.hutchings@...ethink.co.uk>
---
 include/linux/cpumask.h |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index c717f5e..b3d2c1a 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -560,7 +560,7 @@ static inline void cpumask_copy(struct cpumask *dstp,
 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);
 }

 /**
@@ -575,7 +575,7 @@ static inline int cpumask_parselist_user(const char __user *buf, int len,
 				     struct cpumask *dstp)
 {
 	return bitmap_parselist_user(buf, len, cpumask_bits(dstp),
-				     nr_cpu_ids);
+				     nr_cpumask_bits);
 }

 /**
@@ -590,7 +590,7 @@ static inline int cpumask_parse(const char *buf, struct cpumask *dstp)
 	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);
 }

 /**
@@ -602,7 +602,7 @@ static inline int cpumask_parse(const char *buf, struct cpumask *dstp)
  */
 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);
 }

 /**