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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: Chris Bainbridge <chris.bainbridge@gmail.com> Reported-by: Feng Tang <feng.tang@intel.com> Fixes: dd02926 ("clocksource: Improve "skew is too large" messages") Reviewed-by: Feng Tang <feng.tang@intel.com> Tested-by: Chris Bainbridge <chris.bainbridge@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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kernel/time/clocksource.c

Lines changed: 4 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -473,8 +473,8 @@ static void clocksource_watchdog(struct timer_list *unused)
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/* Check the deviation from the watchdog clocksource. */
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md = cs->uncertainty_margin + watchdog->uncertainty_margin;
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if (abs(cs_nsec - wd_nsec) > md) {
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u64 cs_wd_msec;
477-
u64 wd_msec;
476+
s64 cs_wd_msec;
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s64 wd_msec;
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u32 wd_rem;
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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)
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watchdog->name, wd_nsec, wdnow, wdlast, watchdog->mask);
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pr_warn(" '%s' cs_nsec: %lld cs_now: %llx cs_last: %llx mask: %llx\n",
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cs->name, cs_nsec, csnow, cslast, cs->mask);
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cs_wd_msec = div_u64_rem(cs_nsec - wd_nsec, 1000U * 1000U, &wd_rem);
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wd_msec = div_u64_rem(wd_nsec, 1000U * 1000U, &wd_rem);
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cs_wd_msec = div_s64_rem(cs_nsec - wd_nsec, 1000 * 1000, &wd_rem);
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wd_msec = div_s64_rem(wd_nsec, 1000 * 1000, &wd_rem);
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pr_warn(" Clocksource '%s' skewed %lld ns (%lld ms) over watchdog '%s' interval of %lld ns (%lld ms)\n",
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cs->name, cs_nsec - wd_nsec, cs_wd_msec, watchdog->name, wd_nsec, wd_msec);
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if (curr_clocksource == cs)

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