[PATCH AUTOSEL 5.4 182/350] s390/time: ensure get_clock_monotonic() returns monotonic values

Sasha Levin
2019-12-10T21:10:37Z

From: Heiko Carstens <heiko.carstens@de.ibm.com>

[ Upstream commit 011620688a71f2f1fe9901dbc2479a7c01053196 ]

The current implementation of get_clock_monotonic() leaves it up to
the caller to call the function with preemption disabled. The only
core kernel caller (sched_clock) however does not disable preemption.

In order to make sure that all callers of this function see monotonic
values handle disabling preemption within the function itself.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/s390/include/asm/timex.h | 16 ++++++++++------
1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/arch/s390/include/asm/timex.h b/arch/s390/include/asm/timex.h
index 64539c221672b..0f12a3f912820 100644
--- a/arch/s390/include/asm/timex.h
+++ b/arch/s390/include/asm/timex.h
@@ -10,8 +10,9 @@
#ifndef _ASM_S390_TIMEX_H
#define _ASM_S390_TIMEX_H

-#include <asm/lowcore.h>
+#include <linux/preempt.h>
#include <linux/time64.h>
+#include <asm/lowcore.h>

/* The value of the TOD clock for 1.1.1970. */
#define TOD_UNIX_EPOCH 0x7d91048bca000000ULL
@@ -186,15 +187,18 @@ extern unsigned char tod_clock_base[16] __aligned(8);
/**
* get_clock_monotonic - returns current time in clock rate units
*
- * The caller must ensure that preemption is disabled.
* The clock and tod_clock_base get changed via stop_machine.
- * Therefore preemption must be disabled when calling this
- * function, otherwise the returned value is not guaranteed to
- * be monotonic.
+ * Therefore preemption must be disabled, otherwise the returned
+ * value is not guaranteed to be monotonic.
*/
static inline unsigned long long get_tod_clock_monotonic(void)
{
- return get_tod_clock() - *(unsigned long long *) &tod_clock_base[1];
+ unsigned long long tod;
+
+ preempt_disable();
+ tod = get_tod_clock() - *(unsigned long long *) &tod_clock_base[1];
+ preempt_enable();
+ return tod;
}

/**
--
2.20.1