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From:   Jiasheng Jiang <jiasheng@iscas.ac.cn>
To:     valentin.schneider@arm.com, peterz@infradead.org, mingo@kernel.org,
        namit@vmware.com
Cc:     linux-kernel@vger.kernel.org, Jiasheng Jiang <jiasheng@iscas.ac.cn>
Subject: [PATCH] cpumask: Fix implicit type conversion
Date:   Wed, 27 Oct 2021 06:45:23 +0000
Message-Id: <1635317123-2716894-1-git-send-email-jiasheng@iscas.ac.cn>
Precedence: bulk

Since the 'nr_cpu_ids' is unsigned int, then we can assume its
value is (2^32 - 1).
Also, the 'cpu' is unsigned int.
As the number of cycles increases, the value of 'cpu' can be
(2^31 - 1).
Although in the cpumask_next() 'cpu' is implicitly casted to int,
its actual value is also (2^31 - 1).
However, the return value of cpumask_next(), the updated value of
'cpu', is (2^31).
That means the restriction 'cpu < nr_cpu_ids' is still statisfied
and in cpumask_next() when 'cpu' is implicitly casted to int, its
actual value is (-2^31).
Obviously, it is illegal and dangerous for cpumask_next(), as well
as others.
Therefore, we should fix the macro description of 'cpu' that remove
the '(optionally unsigned)' and restrict the value of 'cpu' to be
non-negative integer.
Moreover, all the existing issues should be dealed with.

Fixes: c743f0a ("sched/fair, cpumask: Export for_each_cpu_wrap()")
Fixes: 8bd93a2 ("rcu: Accelerate grace period if last non-dynticked CPU")
Fixes: 984f2f3 ("cpumask: introduce new API, without changing anything, v3")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
---
 include/linux/cpumask.h | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index bfc4690..8a8e59f 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -232,7 +232,7 @@ int cpumask_any_distribute(const struct cpumask *srcp);
 
 /**
  * for_each_cpu - iterate over every cpu in a mask
- * @cpu: the (optionally unsigned) integer iterator
+ * @cpu: the integer iterator
  * @mask: the cpumask pointer
  *
  * After the loop, cpu is >= nr_cpu_ids.
@@ -240,11 +240,11 @@ int cpumask_any_distribute(const struct cpumask *srcp);
 #define for_each_cpu(cpu, mask)				\
 	for ((cpu) = -1;				\
 		(cpu) = cpumask_next((cpu), (mask)),	\
-		(cpu) < nr_cpu_ids;)
+		(cpu) < nr_cpu_ids && (cpu) >= 0;)
 
 /**
  * for_each_cpu_not - iterate over every cpu in a complemented mask
- * @cpu: the (optionally unsigned) integer iterator
+ * @cpu: the integer iterator
  * @mask: the cpumask pointer
  *
  * After the loop, cpu is >= nr_cpu_ids.
@@ -252,13 +252,13 @@ int cpumask_any_distribute(const struct cpumask *srcp);
 #define for_each_cpu_not(cpu, mask)				\
 	for ((cpu) = -1;					\
 		(cpu) = cpumask_next_zero((cpu), (mask)),	\
-		(cpu) < nr_cpu_ids;)
+		(cpu) < nr_cpu_ids && (cpu) >= 0;)
 
 extern int cpumask_next_wrap(int n, const struct cpumask *mask, int start, bool wrap);
 
 /**
  * for_each_cpu_wrap - iterate over every cpu in a mask, starting at a specified location
- * @cpu: the (optionally unsigned) integer iterator
+ * @cpu: the integer iterator
  * @mask: the cpumask poiter
  * @start: the start location
  *
@@ -268,12 +268,12 @@ extern int cpumask_next_wrap(int n, const struct cpumask *mask, int start, bool
  */
 #define for_each_cpu_wrap(cpu, mask, start)					\
 	for ((cpu) = cpumask_next_wrap((start)-1, (mask), (start), false);	\
-	     (cpu) < nr_cpumask_bits;						\
+	     (cpu) < nr_cpumask_bits && (cpu) >= 0;						\
 	     (cpu) = cpumask_next_wrap((cpu), (mask), (start), true))
 
 /**
  * for_each_cpu_and - iterate over every cpu in both masks
- * @cpu: the (optionally unsigned) integer iterator
+ * @cpu: the integer iterator
  * @mask1: the first cpumask pointer
  * @mask2: the second cpumask pointer
  *
@@ -288,7 +288,7 @@ extern int cpumask_next_wrap(int n, const struct cpumask *mask, int start, bool
 #define for_each_cpu_and(cpu, mask1, mask2)				\
 	for ((cpu) = -1;						\
 		(cpu) = cpumask_next_and((cpu), (mask1), (mask2)),	\
-		(cpu) < nr_cpu_ids;)
+		(cpu) < nr_cpu_ids && (cpu) >= 0;)
 #endif /* SMP */
 
 #define CPU_BITS_NONE						\
-- 
2.7.4