Symptom: since upgrading from Fedora 19 (3.16) to Fedora 21 (3.17+) my MythTV infrared blaster (using lirc) stopped working.  It would blast one IR command usually and then stop blasting for a while.  I am using 32-bit PAE on this old MythTV box.

I have successfully bisected and located a commit that is causing my
problem.  Look at commit 166afb64511.  I have confirmed 100% this is causing the problem.

Here's my guess at the bug:
ktime_to_us returns s64, but the commit changes it so ktime_to_us just
returns what ktime_divns returns, and ktime_divns returns a u64!  If the
u64 is big enough, wouldn't it wrap s64 around to a negative number?  Or,
perhaps if some caller is passing in negative ktime_t to begin with it
will trigger without having to hit big numbers.  With my limited knowledge
of C, I am stabbing in the dark here.

This little patch (at bottom of email) that puts the code back in place
and gets rid of the function call fixes the problem for me.  I applied
this patch to the very latest FC21 kernel-PAE-3.19.1-201.fc21.i686 src.rpm
and rpmbuilded and the bug is gone!  I can once again MythTV.  Hooray.

I suspect no one else is seeing this because less people are running
32-bit now, and perhaps in most code paths the value of the u64 never gets
above 2^63.  I suspect something in drivers/media (possibly) is passing
very high or negative values (possibly another bug) to these calls.

Obviously my patch isn't the real solution, the real solution is to make
the new function calls use a consistent 64-bit type, or figure out what in
my code path is calling these functions and check it for value sanity.

I've documented the whole process / details of this bug in RHBZ:
https://bugzilla.redhat.com/show_bug.cgi?id=1200353

diff -uNr a/include/linux/ktime.h b/include/linux/ktime.h
--- a/include/linux/ktime.h     2015-02-08 20:54:22.000000000 -0600
+++ b/include/linux/ktime.h     2015-03-23 01:09:43.000000000 -0500
@@ -173,12 +173,16 @@

 static inline s64 ktime_to_us(const ktime_t kt)
 {
-	return ktime_divns(kt, NSEC_PER_USEC);
+/*     return ktime_divns(kt, NSEC_PER_USEC); */
+	struct timeval tv = ktime_to_timeval(kt);
+	return (s64) tv.tv_sec * USEC_PER_SEC + tv.tv_usec;
 }

 static inline s64 ktime_to_ms(const ktime_t kt)
 {
-	return ktime_divns(kt, NSEC_PER_MSEC);
+/*     return ktime_divns(kt, NSEC_PER_MSEC); */
+	struct timeval tv = ktime_to_timeval(kt);
+	return (s64) tv.tv_sec * MSEC_PER_SEC + tv.tv_usec / USEC_PER_MSEC;
 }

 static inline s64 ktime_us_delta(const ktime_t later, const ktime_t earlier)