Commit e40806e9 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

clocksource: Handle negative skews in "skew is too large" messages 



The nanosecond-to-millisecond skew computation uses unsigned arithmetic,
which produces user-unfriendly large positive numbers for negative skews.
Therefore, use signed arithmetic for this computation in order to preserve
the negativity.

Reported-by: default avatarChris Bainbridge <chris.bainbridge@gmail.com>
Reported-by: default avatarFeng Tang <feng.tang@intel.com>
Fixes: dd029269 ("clocksource: Improve "skew is too large" messages")
Reviewed-by: default avatarFeng Tang <feng.tang@intel.com>
Tested-by: default avatarChris Bainbridge <chris.bainbridge@gmail.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 06c2afb8

kernel/time/clocksource.c

+4 −4
Original line number Diff line number Diff line
@@ -473,8 +473,8 @@ static void clocksource_watchdog(struct timer_list *unused) 
		/* Check the deviation from the watchdog clocksource. */

		md = cs->uncertainty_margin + watchdog->uncertainty_margin;

		if (abs(cs_nsec - wd_nsec) > md) {

			u64 cs_wd_msec;

			u64 wd_msec;

			s64 cs_wd_msec;

			s64 wd_msec;

			u32 wd_rem;



			pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n",
@@ -483,8 +483,8 @@ static void clocksource_watchdog(struct timer_list *unused) 
				watchdog->name, wd_nsec, wdnow, wdlast, watchdog->mask);

			pr_warn("                      '%s' cs_nsec: %lld cs_now: %llx cs_last: %llx mask: %llx\n",

				cs->name, cs_nsec, csnow, cslast, cs->mask);

			cs_wd_msec = div_u64_rem(cs_nsec - wd_nsec, 1000U * 1000U, &wd_rem);

			wd_msec = div_u64_rem(wd_nsec, 1000U * 1000U, &wd_rem);

			cs_wd_msec = div_s64_rem(cs_nsec - wd_nsec, 1000 * 1000, &wd_rem);

			wd_msec = div_s64_rem(wd_nsec, 1000 * 1000, &wd_rem);

			pr_warn("                      Clocksource '%s' skewed %lld ns (%lld ms) over watchdog '%s' interval of %lld ns (%lld ms)\n",

				cs->name, cs_nsec - wd_nsec, cs_wd_msec, watchdog->name, wd_nsec, wd_msec);

			if (curr_clocksource == cs)