linux-kernel - [PATCH] cpuset: Replace all instances of time_t with time64

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Message-ID: <2798266.9VZu01a7d1@wuerfel>
Date:	Wed, 25 Nov 2015 16:16:55 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Li Zefan <lizefan@...wei.com>, cgroups@...r.kernel.org
Cc:	Heena Sirwani <heenasirwani@...il.com>,
	linux-kernel@...r.kernel.org, y2038@...ts.linaro.org,
	tglx@...utronix.de, John Stultz <john.stultz@...aro.org>
Subject: [PATCH] cpuset: Replace all instances of time_t with time64_t

The following patch replaces all instances of time_t with time64_t i.e.
change the type used for representing time from 32-bit to 64-bit. All
32-bit kernels to date use a signed 32-bit time_t type, which can only
represent time until January 2038. Since embedded systems running 32-bit
Linux are going to survive beyond that date, we have to change all
current uses, in a backwards compatible way.

The patch also changes the function get_seconds() that returns a 32-bit
integer to ktime_get_seconds() that returns seconds as 64-bit integer.

The patch changes the type of ticks from time_t to u32. We keep ticks as
32-bits as the function uses 32-bit arithmetic which would prove less
expensive than 64-bit arithmetic and the function is expected to be
called atleast once every 32 seconds.

Signed-off-by: Heena Sirwani <heenasirwani@...il.com>
Reviewed-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
This is an older patch I still had in my queue. Who should pick it up?

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 10ae73611d80..c9ea63ff70a7 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -51,6 +51,7 @@
 #include <linux/stat.h>
 #include <linux/string.h>
 #include <linux/time.h>
+#include <linux/time64.h>
 #include <linux/backing-dev.h>
 #include <linux/sort.h>
 
@@ -68,7 +69,7 @@ struct static_key cpusets_enabled_key __read_mostly = STATIC_KEY_INIT_FALSE;
 struct fmeter {
 	int cnt;		/* unprocessed events count */
 	int val;		/* most recent output value */
-	time_t time;		/* clock (secs) when val computed */
+	time64_t time;		/* clock (secs) when val computed */
 	spinlock_t lock;	/* guards read or write of above */
 };
 
@@ -1374,7 +1375,7 @@ out:
  */
 
 #define FM_COEF 933		/* coefficient for half-life of 10 secs */
-#define FM_MAXTICKS ((time_t)99) /* useless computing more ticks than this */
+#define FM_MAXTICKS ((u32)99)   /* useless computing more ticks than this */
 #define FM_MAXCNT 1000000	/* limit cnt to avoid overflow */
 #define FM_SCALE 1000		/* faux fixed point scale */
 
@@ -1390,8 +1391,11 @@ static void fmeter_init(struct fmeter *fmp)
 /* Internal meter update - process cnt events and update value */
 static void fmeter_update(struct fmeter *fmp)
 {
-	time_t now = get_seconds();
-	time_t ticks = now - fmp->time;
+	time64_t now;
+	u32 ticks;
+
+	now = ktime_get_seconds();
+	ticks = now - fmp->time;
 
 	if (ticks == 0)
 		return;

--
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