Re: BUG: assert spuriously fails in selftest/proc/proc-uptime-001.c

[Mirsad Goran Todorovac]

On 06. 01. 2023. 22:18, Mirsad Goran Todorovac wrote:
> Hi all,
>
> In the same environment as the previous bug report (Lenovo Ideapad 3 15ITL6 laptop
> running Ubuntu 22.10 kinetic kudu and 6.2-rc2 vanilla Torvalds tree kernel), the
> next test in the ...selftest/proc/* sequence spuriously fails in assert (i1 <= i0).
>
> Please note that the compiler is the novelty GCC 12.2.0-3ubuntu1.
>
> This was previously hidden by premature hang in the `make kselftest` run due to
> proc-empty-vm an proc-pid-vm problems that are now fixed.
>
> root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
> root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
> root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
> proc-uptime-001: proc-uptime-001.c:39: main: Assertion `i1 >= i0' failed.
> Aborted (core dumped)
> root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
> proc-uptime-001: proc-uptime-001.c:39: main: Assertion `i1 >= i0' failed.
> Aborted (core dumped)
> root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
> root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
> root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
> root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
> root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
> proc-uptime-001: proc-uptime-001.c:39: main: Assertion `i1 >= i0' failed.
> Aborted (core dumped)
> root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
> root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
> proc-uptime-001: proc-uptime-001.c:39: main: Assertion `i1 >= i0' failed.
> Aborted (core dumped)
> root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
> root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
> proc-uptime-001: proc-uptime-001.c:39: main: Assertion `i1 >= i0' failed.
> Aborted (core dumped)
> root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
> root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
> root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
> proc-uptime-001: proc-uptime-001.c:39: main: Assertion `i1 >= i0' failed.
> Aborted (core dumped)
> root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
> proc-uptime-001: proc-uptime-001.c:39: main: Assertion `i1 >= i0' failed.
> Aborted (core dumped)
> root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
> proc-uptime-001: proc-uptime-001.c:39: main: Assertion `i1 >= i0' failed.
> Aborted (core dumped)
> root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
> proc-uptime-001: proc-uptime-001.c:39: main: Assertion `i1 >= i0' failed.
> Aborted (core dumped)
> root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
> proc-uptime-001: proc-uptime-001.c:39: main: Assertion `i1 >= i0' failed.
> Aborted (core dumped)
> root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
> proc-uptime-001: proc-uptime-001.c:39: main: Assertion `i1 >= i0' failed.
> Aborted (core dumped)
> root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
>
> It happens about half of the times the program is called.
>
> The source seems OK, I can't tell why the idle counter doesn't look monotonic to
> the program.
>
> Hope this helps.
>
> BTW, good news: this time I have checked independently, and this is the last test from the .../selftest/proc
> group that doesn't have clean exit code 0.

UPDATE:

The same behavior independently occurred with GCC 10.4.0, 9.5.0, 8.5.0 and 6.5.0.

Apparently this happens in 30% to 50% of attempts. Perhaps that's why it wasn't discovered yet:

root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# make CC=gcc-10
gcc-10 -Wall -O2 -Wno-unused-function -D_GNU_SOURCE   -pthread   fd-001-lookup.c  -o 
/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc/fd-001-lookup
gcc-10 -Wall -O2 -Wno-unused-function -D_GNU_SOURCE   -pthread   fd-002-posix-eq.c  -o 
/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc/fd-002-posix-eq
gcc-10 -Wall -O2 -Wno-unused-function -D_GNU_SOURCE   -pthread   fd-003-kthread.c  -o 
/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc/fd-003-kthread
gcc-10 -Wall -O2 -Wno-unused-function -D_GNU_SOURCE   -pthread   proc-loadavg-001.c  -o 
/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc/proc-loadavg-001
gcc-10 -Wall -O2 -Wno-unused-function -D_GNU_SOURCE   -pthread   proc-empty-vm.c  -o 
/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc/proc-empty-vm
gcc-10 -Wall -O2 -Wno-unused-function -D_GNU_SOURCE   -pthread   proc-pid-vm.c  -o 
/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc/proc-pid-vm
gcc-10 -Wall -O2 -Wno-unused-function -D_GNU_SOURCE   -pthread   proc-self-map-files-001.c  -o 
/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc/proc-self-map-files-001
gcc-10 -Wall -O2 -Wno-unused-function -D_GNU_SOURCE   -pthread   proc-self-map-files-002.c  -o 
/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc/proc-self-map-files-002
gcc-10 -Wall -O2 -Wno-unused-function -D_GNU_SOURCE   -pthread   proc-self-syscall.c  -o 
/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc/proc-self-syscall
gcc-10 -Wall -O2 -Wno-unused-function -D_GNU_SOURCE   -pthread   proc-self-wchan.c  -o 
/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc/proc-self-wchan
gcc-10 -Wall -O2 -Wno-unused-function -D_GNU_SOURCE   -pthread   proc-subset-pid.c  -o 
/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc/proc-subset-pid
gcc-10 -Wall -O2 -Wno-unused-function -D_GNU_SOURCE   -pthread   proc-tid0.c  -o 
/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc/proc-tid0
gcc-10 -Wall -O2 -Wno-unused-function -D_GNU_SOURCE   -pthread   proc-uptime-001.c  -o 
/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc/proc-uptime-001
gcc-10 -Wall -O2 -Wno-unused-function -D_GNU_SOURCE   -pthread   proc-uptime-002.c  -o 
/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc/proc-uptime-002
gcc-10 -Wall -O2 -Wno-unused-function -D_GNU_SOURCE   -pthread   read.c  -o 
/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc/read
gcc-10 -Wall -O2 -Wno-unused-function -D_GNU_SOURCE   -pthread   self.c  -o 
/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc/self
gcc-10 -Wall -O2 -Wno-unused-function -D_GNU_SOURCE   -pthread   setns-dcache.c  -o 
/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc/setns-dcache
gcc-10 -Wall -O2 -Wno-unused-function -D_GNU_SOURCE   -pthread   setns-sysvipc.c  -o 
/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc/setns-sysvipc
gcc-10 -Wall -O2 -Wno-unused-function -D_GNU_SOURCE   -pthread   thread-self.c  -o 
/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc/thread-self
gcc-10 -Wall -O2 -Wno-unused-function -D_GNU_SOURCE   -pthread   proc-multiple-procfs.c  -o 
/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc/proc-multiple-procfs
gcc-10 -Wall -O2 -Wno-unused-function -D_GNU_SOURCE   -pthread   proc-fsconfig-hidepid.c  -o 
/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc/proc-fsconfig-hidepid
root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# for exe in `ls -l | grep -e -x | 
awk '{ print $9 }'`; do echo -n ${exe}':'; ./$exe ; echo "exit=$?" ; done
fd-001-lookup:exit=0
fd-002-posix-eq:exit=0
fd-003-kthread:exit=0
proc-empty-vm:exit=0
proc-fsconfig-hidepid:exit=0
proc-loadavg-001:exit=0
proc-multiple-procfs:exit=0
proc-pid-vm:exit=0
proc-self-map-files-001:exit=0
proc-self-map-files-002:exit=0
proc-self-syscall:exit=0
proc-self-wchan:exit=0
proc-subset-pid:exit=0
proc-tid0:exit=0
proc-uptime-001:exit=0
proc-uptime-002:exit=0
read:exit=0
self:exit=0
setns-dcache:exit=0
setns-sysvipc:exit=0
thread-self:exit=0
root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
proc-uptime-001: proc-uptime-001.c:39: main: Assertion `i1 >= i0' failed.
Aborted (core dumped)
root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
proc-uptime-001: proc-uptime-001.c:39: main: Assertion `i1 >= i0' failed.
Aborted (core dumped)
root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
proc-uptime-001: proc-uptime-001.c:39: main: Assertion `i1 >= i0' failed.
Aborted (core dumped)
root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001
root@marvin-IdeaPad-3-15ITL6:/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/proc# ./proc-uptime-001

The conclusion (to state the obvious) is that the GCC 12.2.0 optimisations are
not the culprit this time :-/

Thanks,
Mirsad

--
Mirsad Goran Todorovac
Sistem inženjer
Grafički fakultet | Akademija likovnih umjetnosti
Sveučilište u Zagrebu
--
System engineer
Faculty of Graphic Arts | Academy of Fine Arts
University of Zagreb, Republic of Croatia
The European Union