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Date:   Wed, 6 Dec 2017 15:39:51 -0600
From:   Jason Wessel <jason.wessel@...driver.com>
To:     Daniel Thompson <daniel.thompson@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>
CC:     Thomas Gleixner <tglx@...utronix.de>, <y2038@...ts.linaro.org>,
        John Stultz <john.stultz@...aro.org>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        Ingo Molnar <mingo@...nel.org>, <linux-kernel@...r.kernel.org>,
        <kgdb-bugreport@...ts.sourceforge.net>
Subject: Re: [PATCH] kdb: use __ktime_get_real_seconds instead of
 __current_kernel_time

On 10/13/2017 03:26 AM, Daniel Thompson wrote:
> On 12/10/17 23:40, Andrew Morton wrote:
>> On Thu, 12 Oct 2017 16:06:11 +0200 Arnd Bergmann <arnd@...db.de> wrote:
>>
>>> kdb is the only user of the __current_kernel_time() interface, which is
>>> not y2038 safe and should be removed at some point.
>>>
>>> The kdb code also goes to great lengths to print the time in a
>>> human-readable format from 'struct timespec', again using a non-y2038-safe
>>> re-implementation of the generic time_to_tm() code.
>>
>> Is it really necessary for the kdb `summary' command to print the
>> time/date?  Which puppies would die if we just removed it all?
> 
> kdb may enter spontaneously (BUG(), etc) so it can be useful if one
> returns from an overnight test run to know how long things survived.
> 
> It would almost certainly be possible for a skilled user to reconstruct
> the time of death. Having said that, one of the things you can do with
> kdb (although I admit *I* have never done it) is leave a macro command
> in the hands of an unskilled user.
> 
> Short summary: no puppies would die, but perhaps some might go hungry
> for a little while when their owner is late home?
> 

Daniel is correct.  This is information that was just a nice to have for postmortem analysis it can also be called via gdb macros.

If kdb is really the last remaining user, it seems like the interface should get removed and kdb can print time another way that is compatible with the 2038 fixes.

After having taken a quick look it would seem __ktime_get_real_seconds()  (because we need the non-lock protected version) and time64_to_tm() should be the proper replacement.  There is certainly no reason to duplicate code in kdb for the "summary" functions.

I am assuming no one has fixed this yet, so I should be able to provide a patch to the list along the lines of what is below.  And I will follow it with a second patch to remove the __current_kernel_time() to lkml and the timekeeper maintainer.

Cheers,
Jason.

diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index 09168c52ab64..2529cc470a45 100644
--- a/include/linux/timekeeping.h
+++ b/include/linux/timekeeping.h
@@ -53,6 +53,8 @@ extern void getrawmonotonic64(struct timespec64 *ts);
  extern void ktime_get_ts64(struct timespec64 *ts);
  extern time64_t ktime_get_seconds(void);
  extern time64_t ktime_get_real_seconds(void);
+/* does not take xtime_lock */
+extern time64_t __ktime_get_real_seconds(void);
  
  extern int __getnstimeofday64(struct timespec64 *tv);
  extern void getnstimeofday64(struct timespec64 *tv);
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 2a20c0dfdafc..c7a02710d884 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -2477,41 +2477,6 @@ static int kdb_kill(int argc, const char **argv)
  	return 0;
  }
  
-struct kdb_tm {
-	int tm_sec;	/* seconds */
-	int tm_min;	/* minutes */
-	int tm_hour;	/* hours */
-	int tm_mday;	/* day of the month */
-	int tm_mon;	/* month */
-	int tm_year;	/* year */
-};
-
-static void kdb_gmtime(struct timespec *tv, struct kdb_tm *tm)
-{
-	/* This will work from 1970-2099, 2100 is not a leap year */
-	static int mon_day[] = { 31, 29, 31, 30, 31, 30, 31,
-				 31, 30, 31, 30, 31 };
-	memset(tm, 0, sizeof(*tm));
-	tm->tm_sec  = tv->tv_sec % (24 * 60 * 60);
-	tm->tm_mday = tv->tv_sec / (24 * 60 * 60) +
-		(2 * 365 + 1); /* shift base from 1970 to 1968 */
-	tm->tm_min =  tm->tm_sec / 60 % 60;
-	tm->tm_hour = tm->tm_sec / 60 / 60;
-	tm->tm_sec =  tm->tm_sec % 60;
-	tm->tm_year = 68 + 4*(tm->tm_mday / (4*365+1));
-	tm->tm_mday %= (4*365+1);
-	mon_day[1] = 29;
-	while (tm->tm_mday >= mon_day[tm->tm_mon]) {
-		tm->tm_mday -= mon_day[tm->tm_mon];
-		if (++tm->tm_mon == 12) {
-			tm->tm_mon = 0;
-			++tm->tm_year;
-			mon_day[1] = 28;
-		}
-	}
-	++tm->tm_mday;
-}
-
  /*
   * Most of this code has been lifted from kernel/timer.c::sys_sysinfo().
   * I cannot call that code directly from kdb, it has an unconditional
@@ -2537,8 +2502,8 @@ static void kdb_sysinfo(struct sysinfo *val)
   */
  static int kdb_summary(int argc, const char **argv)
  {
-	struct timespec now;
-	struct kdb_tm tm;
+	time64_t now_seconds;
+	struct tm tm;
  	struct sysinfo val;
  
  	if (argc)
@@ -2552,9 +2517,9 @@ static int kdb_summary(int argc, const char **argv)
  	kdb_printf("domainname %s\n", init_uts_ns.name.domainname);
  	kdb_printf("ccversion  %s\n", __stringify(CCVERSION));
  
-	now = __current_kernel_time();
-	kdb_gmtime(&now, &tm);
-	kdb_printf("date       %04d-%02d-%02d %02d:%02d:%02d "
+	now_seconds = __ktime_get_real_seconds();
+	time64_to_tm(now_seconds, sys_tz.tz_minuteswest * 60, &tm);
+	kdb_printf("date       %04ld-%02d-%02d %02d:%02d:%02d "
  		   "tz_minuteswest %d\n",
  		1900+tm.tm_year, tm.tm_mon+1, tm.tm_mday,
  		tm.tm_hour, tm.tm_min, tm.tm_sec,

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