Ah, I see now what is happening. The userspace code is dealing with
microseconds, while the syscalls all deal with nanoseconds.
So, when using absolute time, we read the clock (in nanoseconds), add
that to our microseconds value after converting (that is, rounding the
value), then set the timer, and read it back.
Take this run, for example:
[pid 27982] timer_create(CLOCK_MONOTONIC, NULL, [0]) = 0
[pid 27982] clock_gettime(CLOCK_MONOTONIC, {tv_sec=53718, tv_nsec=537178810}) = 0
[pid 27982] timer_settime(0, TIMER_ABSTIME, {it_interval={tv_sec=0, tv_nsec=0},
it_value={tv_sec=53718, tv_nsec=587179000}}, {it_interval={tv_sec=0,
tv_nsec=0}, it_value={tv_sec=0, tv_nsec=0}}) = 0
[pid 27982] timer_gettime(0, {it_interval={tv_sec=0, tv_nsec=0},
it_value={tv_sec=0, tv_nsec=49842203}}) = 0
We read the time and set it 587179000 - 537178810 = 50000190 nanoseconds
in the future, which is more than our 50000 microseconds. No surprise
that, if you are fast enough, you are going to read a larger value back.
Not a kernel bug!
Cascardo.
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https://bugs.launchpad.net/bugs/1898633
Title:
timer_settime01 from ubuntu_ltp_syscalls failed on bionic /aws-4.15
on c5.metal
Status in ubuntu-kernel-tests:
New
Status in linux-aws package in Ubuntu:
New
Status in linux-aws source package in Bionic:
New
Bug description:
21367. 09/25 08:38:06 DEBUG| utils:0153| [stdout] startup='Fri Sep 25
08:37:00 2020'
21368. 09/25 08:38:06 DEBUG| utils:0153| [stdout] tst_test.c:1250:
TINFO: Timeout per run is 0h 05m 00s
21369. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:85: TINFO: Testing variant: syscall with old kernel spec
21370. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:96: TINFO: Testing for general initialization:
21371. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_REALTIME) passed
21372. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_MONOTONIC) passed
21373. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_PROCESS_CPUTIME_ID) passed
21374. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_THREAD_CPUTIME_ID) passed
21375. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_BOOTTIME) passed
21376. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_BOOTTIME_ALARM) passed
21377. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_REALTIME_ALARM) passed
21378. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_TAI) passed
21379. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:96: TINFO: Testing for setting old_value:
21380. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_REALTIME) passed
21381. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_MONOTONIC) passed
21382. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_PROCESS_CPUTIME_ID) passed
21383. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_THREAD_CPUTIME_ID) passed
21384. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_BOOTTIME) passed
21385. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_BOOTTIME_ALARM) passed
21386. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_REALTIME_ALARM) passed
21387. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_TAI) passed
21388. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:96: TINFO: Testing for using periodic timer:
21389. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_REALTIME) passed
21390. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_MONOTONIC) passed
21391. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_PROCESS_CPUTIME_ID) passed
21392. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_THREAD_CPUTIME_ID) passed
21393. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_BOOTTIME) passed
21394. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_BOOTTIME_ALARM) passed
21395. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_REALTIME_ALARM) passed
21396. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_TAI) passed
21397. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:96: TINFO: Testing for using absolute time:
21398. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_REALTIME) passed
21399. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:160: TFAIL: timer_gettime(CLOCK_MONOTONIC) reported bad
values (0: 50000034): SUCCESS (0)
21400. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_MONOTONIC) passed
21401. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_PROCESS_CPUTIME_ID) passed
21402. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_THREAD_CPUTIME_ID) passed
21403. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_BOOTTIME) passed
21404. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_BOOTTIME_ALARM) passed
21405. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_REALTIME_ALARM) passed
21406. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
timer_settime01.c:170: TPASS: timer_settime(CLOCK_TAI) passed
21407. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
21408. 09/25 08:38:06 DEBUG| utils:0153| [stdout] HINT: You _MAY_ be
missing kernel fixes, see:
21409. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
21410. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f18ddc13af98
21411. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e86fea764991
21412. 09/25 08:38:06 DEBUG| utils:0153| [stdout]
21413. 09/25 08:38:06 DEBUG| utils:0153| [stdout] Summary:
21414. 09/25 08:38:06 DEBUG| utils:0153| [stdout] passed 32
21415. 09/25 08:38:06 DEBUG| utils:0153| [stdout] failed 1
21416. 09/25 08:38:06 DEBUG| utils:0153| [stdout] skipped 0
21417. 09/25 08:38:06 DEBUG| utils:0153| [stdout] warnings 0
21418. 09/25 08:38:06 DEBUG| utils:0153| [stdout] tag=timer_settime01
stime=1601023020 dur=2 exit=exited stat=1 core=no cu=202 cs=0
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