linux-kernel - Re: vdso clock_gettime() sometimes broken after sleep

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Date:	Sat, 20 Feb 2016 13:01:40 +0100
From:	Hauke Mehrtens <hauke@...ke-m.de>
To:	markos.chandras@...tec.com, Alex Smith <alex.smith@...tec.com>
Cc:	Ralf Baechle <ralf@...ux-mips.org>, linux-mips@...ux-mips.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: vdso clock_gettime() sometimes broken after sleep

On 01/29/2016 10:32 PM, Hauke Mehrtens wrote:
> When using the vdso clock_gettime() it looks like that the clock is
> sometimes not going forward when the process sleeps and the clock also
> sleeps. This problem only happens with the vdso clock and not with the
> normal syscall clock.
> 
> I wrote a small test program which calls the syscall and the vdso
> version. In the first call they are showing the same time, but after I
> sleeped for 1 second, they are off by one second. This problem occurs
> not 100% reliable but I see it pretty often. Only the CLOCK_REALTIME and
> CLOCK_MONOTONIC seam to be affected CLOCK_REALTIME_COARSE is not affected.
> 
> I am using an MIPS BE 34Kc V5.6 CPU with two VPEs, but only one is used.
> This is a Lantiq VRX200 SoC with OpenWrt Linux kernel 4.4 and musl libc.
> 
> Hauke

Hi,

Any news on this? For me this is a usespace API regression. Should I
send a patch deactivating the vdso support only for the MIPS 34Kc CPU or
for completely for mips?

Hauke


> Here are my measurements:
> 
> start test
> syscall: CLOCK_REALTIME: tv_sec: 1454098944, tv_nsec: 463189916
> vdso:    CLOCK_REALTIME: tv_sec: 1454098944, tv_nsec: 463242196
> syscall: CLOCK_REALTIME_COARSE: tv_sec: 1454098944, tv_nsec: 456000000
> vdso:    CLOCK_REALTIME_COARSE: tv_sec: 1454098944, tv_nsec: 456000000
> syscall: CLOCK_MONOTONIC: tv_sec: 107, tv_nsec: 28113172
> vdso:    CLOCK_MONOTONIC: tv_sec: 107, tv_nsec: 32150208
> syscall: CLOCK_MONOTONIC_COARSE: tv_sec: 107, tv_nsec: 24678324
> vdso:    CLOCK_MONOTONIC_COARSE: tv_sec: 107, tv_nsec: 24678324
> syscall: CLOCK_MONOTONIC_RAW: tv_sec: 107, tv_nsec: 28263008
> vdso:    CLOCK_MONOTONIC_RAW: tv_sec: 107, tv_nsec: 28300760
> syscall: CLOCK_BOOTTIME: tv_sec: 107, tv_nsec: 28337540
> vdso:    CLOCK_BOOTTIME: tv_sec: 107, tv_nsec: 28379100
> syscall: CLOCK_PROCESS_CPUTIME_ID: tv_sec: 0, tv_nsec: 3111128
> vdso:    CLOCK_PROCESS_CPUTIME_ID: tv_sec: 0, tv_nsec: 3153120
> syscall: CLOCK_THREAD_CPUTIME_ID: tv_sec: 0, tv_nsec: 3192208
> vdso:    CLOCK_THREAD_CPUTIME_ID: tv_sec: 0, tv_nsec: 3231696
> sleep(1)
> syscall: CLOCK_REALTIME: tv_sec: 1454098945, tv_nsec: 464023036
> vdso:    CLOCK_REALTIME: tv_sec: 1454098946, tv_nsec: 468077456
> syscall: CLOCK_REALTIME_COARSE: tv_sec: 1454098945, tv_nsec: 460000000
> vdso:    CLOCK_REALTIME_COARSE: tv_sec: 1454098945, tv_nsec: 460000000
> syscall: CLOCK_MONOTONIC: tv_sec: 108, tv_nsec: 28874940
> vdso:    CLOCK_MONOTONIC: tv_sec: 109, tv_nsec: 32911852
> syscall: CLOCK_MONOTONIC_COARSE: tv_sec: 108, tv_nsec: 24678324
> vdso:    CLOCK_MONOTONIC_COARSE: tv_sec: 108, tv_nsec: 24678324
> syscall: CLOCK_MONOTONIC_RAW: tv_sec: 108, tv_nsec: 29023384
> vdso:    CLOCK_MONOTONIC_RAW: tv_sec: 108, tv_nsec: 29061372
> syscall: CLOCK_BOOTTIME: tv_sec: 108, tv_nsec: 29097912
> vdso:    CLOCK_BOOTTIME: tv_sec: 108, tv_nsec: 29139864
> syscall: CLOCK_PROCESS_CPUTIME_ID: tv_sec: 0, tv_nsec: 3824540
> vdso:    CLOCK_PROCESS_CPUTIME_ID: tv_sec: 0, tv_nsec: 3865708
> syscall: CLOCK_THREAD_CPUTIME_ID: tv_sec: 0, tv_nsec: 3904680
> vdso:    CLOCK_THREAD_CPUTIME_ID: tv_sec: 0, tv_nsec: 3943892
> sleep(2)
> syscall: CLOCK_REALTIME: tv_sec: 1454098947, tv_nsec: 464791376
> vdso:    CLOCK_REALTIME: tv_sec: 1454098950, tv_nsec: 468847600
> syscall: CLOCK_REALTIME_COARSE: tv_sec: 1454098947, tv_nsec: 460000000
> vdso:    CLOCK_REALTIME_COARSE: tv_sec: 1454098947, tv_nsec: 460000000
> syscall: CLOCK_MONOTONIC: tv_sec: 110, tv_nsec: 29644468
> vdso:    CLOCK_MONOTONIC: tv_sec: 113, tv_nsec: 33682152
> syscall: CLOCK_MONOTONIC_COARSE: tv_sec: 110, tv_nsec: 24678324
> vdso:    CLOCK_MONOTONIC_COARSE: tv_sec: 110, tv_nsec: 24678324
> syscall: CLOCK_MONOTONIC_RAW: tv_sec: 110, tv_nsec: 29794136
> vdso:    CLOCK_MONOTONIC_RAW: tv_sec: 110, tv_nsec: 29831728
> syscall: CLOCK_BOOTTIME: tv_sec: 110, tv_nsec: 29868576
> vdso:    CLOCK_BOOTTIME: tv_sec: 110, tv_nsec: 29909920
> syscall: CLOCK_PROCESS_CPUTIME_ID: tv_sec: 0, tv_nsec: 4547416
> vdso:    CLOCK_PROCESS_CPUTIME_ID: tv_sec: 0, tv_nsec: 4589684
> syscall: CLOCK_THREAD_CPUTIME_ID: tv_sec: 0, tv_nsec: 4628872
> vdso:    CLOCK_THREAD_CPUTIME_ID: tv_sec: 0, tv_nsec: 4668808
> sleep(3)
> syscall: CLOCK_REALTIME: tv_sec: 1454098950, tv_nsec: 465558716
> vdso:    CLOCK_REALTIME: tv_sec: 1454098956, tv_nsec: 469613960
> syscall: CLOCK_REALTIME_COARSE: tv_sec: 1454098950, tv_nsec: 460000000
> vdso:    CLOCK_REALTIME_COARSE: tv_sec: 1454098950, tv_nsec: 460000000
> syscall: CLOCK_MONOTONIC: tv_sec: 113, tv_nsec: 30411308
> vdso:    CLOCK_MONOTONIC: tv_sec: 119, tv_nsec: 34448236
> syscall: CLOCK_MONOTONIC_COARSE: tv_sec: 113, tv_nsec: 24678324
> vdso:    CLOCK_MONOTONIC_COARSE: tv_sec: 113, tv_nsec: 24678324
> syscall: CLOCK_MONOTONIC_RAW: tv_sec: 113, tv_nsec: 30559184
> vdso:    CLOCK_MONOTONIC_RAW: tv_sec: 113, tv_nsec: 30596676
> syscall: CLOCK_BOOTTIME: tv_sec: 113, tv_nsec: 30632568
> vdso:    CLOCK_BOOTTIME: tv_sec: 113, tv_nsec: 30673204
> syscall: CLOCK_PROCESS_CPUTIME_ID: tv_sec: 0, tv_nsec: 5262328
> vdso:    CLOCK_PROCESS_CPUTIME_ID: tv_sec: 0, tv_nsec: 5304576
> syscall: CLOCK_THREAD_CPUTIME_ID: tv_sec: 0, tv_nsec: 5343136
> vdso:    CLOCK_THREAD_CPUTIME_ID: tv_sec: 0, tv_nsec: 5382616
>