From: Heiko Carstens <hca@linux.ibm.com>
Date: Fri, 21 Mar 2025 12:22:15 +0000 (+0100)
Subject: s390/processor: Use bitop functions for cpu flag helper functions
X-Git-Tag: v6.15-rc1~15^2~5
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=3232f1c8086506c5728f46e5a0d59b860c303b8d;p=thirdparty%2Flinux.git

s390/processor: Use bitop functions for cpu flag helper functions

Use bitop functions to implement cpu flag helper functions. This way
it is guaranteed that bits cannot get lost if modified in different
contexts on a cpu.

E.g. if process context is interrupted in the middle of a
read-modify-write sequence while modifying cpu flags, and within
interrupt context cpu flags are also modified, bits can get lost.

There is currently no code which is doing this, however upcoming code
could potentially run into this problem.

Acked-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
---

diff --git a/arch/s390/include/asm/processor.h b/arch/s390/include/asm/processor.h
index d09a92db95f70..6c8063cb8fe76 100644
--- a/arch/s390/include/asm/processor.h
+++ b/arch/s390/include/asm/processor.h
@@ -31,6 +31,7 @@
 #include <linux/cpumask.h>
 #include <linux/linkage.h>
 #include <linux/irqflags.h>
+#include <linux/bitops.h>
 #include <asm/fpu-types.h>
 #include <asm/cpu.h>
 #include <asm/page.h>
@@ -62,33 +63,27 @@ static __always_inline struct pcpu *this_pcpu(void)
 
 static __always_inline void set_cpu_flag(int flag)
 {
-	this_pcpu()->flags |= (1UL << flag);
+	set_bit(flag, &this_pcpu()->flags);
 }
 
 static __always_inline void clear_cpu_flag(int flag)
 {
-	this_pcpu()->flags &= ~(1UL << flag);
+	clear_bit(flag, &this_pcpu()->flags);
 }
 
 static __always_inline bool test_cpu_flag(int flag)
 {
-	return this_pcpu()->flags & (1UL << flag);
+	return test_bit(flag, &this_pcpu()->flags);
 }
 
 static __always_inline bool test_and_set_cpu_flag(int flag)
 {
-	if (test_cpu_flag(flag))
-		return true;
-	set_cpu_flag(flag);
-	return false;
+	return test_and_set_bit(flag, &this_pcpu()->flags);
 }
 
 static __always_inline bool test_and_clear_cpu_flag(int flag)
 {
-	if (!test_cpu_flag(flag))
-		return false;
-	clear_cpu_flag(flag);
-	return true;
+	return test_and_clear_bit(flag, &this_pcpu()->flags);
 }
 
 /*
@@ -97,7 +92,7 @@ static __always_inline bool test_and_clear_cpu_flag(int flag)
  */
 static __always_inline bool test_cpu_flag_of(int flag, int cpu)
 {
-	return per_cpu(pcpu_devices, cpu).flags & (1UL << flag);
+	return test_bit(flag, &per_cpu(pcpu_devices, cpu).flags);
 }
 
 #define arch_needs_cpu() test_cpu_flag(CIF_NOHZ_DELAY)