linux-kernel - setitimer() doesn't work properly starting with 4.8-rc1

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Date:	Wed, 17 Aug 2016 12:01:20 -0700
From:	Andrei Vagin <avagin@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: setitimer() doesn't work properly starting with 4.8-rc1

Hello,

I found that setitimer() doesn't work properly on out test AMD fitlet.
It works correctly in the 4.7 kernel and doesn't work in 4.8-rc1.

A small test is attached to this message.

[root@...-LAN-dhcp-38 ~]# uname -a
Linux usr-LAN-dhcp-38.99.sw.ru 4.8.0-0.rc2.git1.1.fc25.x86_64 #1 SMP
Tue Aug 16 22:08:16 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
[root@...-LAN-dhcp-38 ~]# strace ./test-timers
...
rt_sigaction(SIGVTALRM, {0x400606, [VTALRM], SA_RESTORER|SA_RESTART,
0x7f51e0d67770}, {SIG_DFL, [], 0}, 8) = 0
setitimer(ITIMER_VIRTUAL, {it_interval={0, 100000}, it_value={0,
100}}, NULL) = 0
exit_group(0)                           = ?
+++ exited with 0 +++

We can see that a test didn't get any signals. When timers works, this
output looks like this:
rt_sigaction(SIGALRM, {0x400606, [ALRM], SA_RESTORER|SA_RESTART,
0x7f9e21b1b770}, {SIG_DFL, [], 0}, 8) = 0
setitimer(ITIMER_REAL, {it_interval={0, 100000}, it_value={0, 100}}, NULL) = 0
--- SIGALRM {si_signo=SIGALRM, si_code=SI_KERNEL} ---
rt_sigreturn({mask=[]})                 = 6295208
--- SIGALRM {si_signo=SIGALRM, si_code=SI_KERNEL} ---
rt_sigreturn({mask=[]})                 = 0
--- SIGALRM {si_signo=SIGALRM, si_code=SI_KERNEL} ---
rt_sigreturn({mask=[]})                 = 1
--- SIGALRM {si_signo=SIGALRM, si_code=SI_KERNEL} ---
rt_sigreturn({mask=[]})                 = 1
--- SIGALRM {si_signo=SIGALRM, si_code=SI_KERNEL} ---
rt_sigreturn({mask=[]})                 = 1471459909
--- SIGALRM {si_signo=SIGALRM, si_code=SI_KERNEL} ---
rt_sigreturn({mask=[]})                 = 1
--- SIGALRM {si_signo=SIGALRM, si_code=SI_KERNEL} ---


Only ITIMER_PROF and ITIMER_VIRTUAL doesn't work properly. ITIMER_REAL
works as expected.

[root@...-LAN-dhcp-38 ~]# cat /proc/cpuinfo
processor : 0
vendor_id : AuthenticAMD
cpu family : 22
model : 48
model name : AMD A10 Micro-6700T APU+AMD Radeon R6 Graphics
stepping : 1
microcode : 0x7030105
cpu MHz : 1000.000
cache size : 2048 KB
physical id : 0
siblings : 4
core id : 0
cpu cores : 4
apicid : 0
initial apicid : 0
fpu : yes
fpu_exception : yes
cpuid level : 13
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt
pdpe1gb rdtscp lm constant_tsc rep_good acc_power nopl nonstop_tsc
extd_apicid aperfmperf eagerfpu pni pclmulqdq monitor ssse3 cx16
sse4_1 sse4_2 movbe popcnt aes xsave avx f16c rdrand lahf_lm
cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch
osvw ibs skinit wdt topoext perfctr_nb bpext ptsc perfctr_l2 cpb
hw_pstate vmmcall bmi1 xsaveopt arat npt lbrv svm_lock nrip_save
tsc_scale flushbyasid decodeassists pausefilter pfthreshold
overflow_recov
bugs : fxsave_leak sysret_ss_attrs null_seg
bogomips : 2395.40
TLB size : 1024 4K pages
clflush size : 64
cache_alignment : 64
address sizes : 40 bits physical, 48 bits virtual
power management: ts ttp tm 100mhzsteps hwpstate cpb acc_power [13]

This problem was caught by criu tests:
https://github.com/xemul/criu/issues/200

Thanks,
Andrei

View attachment "test-timers.c" of type "text/x-csrc" (811 bytes)