[uclibc-ng-devel] Re: 100% CPU Issue in rsyslog's pthread_cond_wait() on m68k

Thu, 13 Mar 2025 00:36:13 -0700 

Hi Waldemar,

On 13/03/2025 07:59, Waldemar Brodkorb wrote:

Hi,

Thorsten made a fix for the issue. I verified that it works.
See git master. It was an alignment problem specific to m68k
architecture in the NPTL code. You need to rebuild rsyslog and
all dependent libraries to take effect of the fix.


I tested it, and it works fine now !
Thanks a lot !

BR,
JM


best regards
  Waldemar

Jean-Michel Hautbois wrote,


Hi there,

I have a quite complex issue, with uclibc-ng (master branch). Here is a
summary.

Tested with qemu (buildroot for q800) on the m68k architecture, rsyslog
consumes 100% CPU during its pthread_cond_wait() calls.

This is in [1] in the doIdleProcessing() function.

Using glibc+m68k does not reveal this issue, and uclibc-ng on arm doesn't
either.

Strace output shows that the futex_time64() syscall is repeatedly returning
EINVAL, indicating that the call is looping without proper blocking:
# strace -f rsyslogd -dn
<snip>
[pid   110] write(1, "9139.913444393:main Q:Reg/w0  : "...,
859139.913444393:main Q:Reg/w0  : wti.c: main Q:Reg/w0: worker IDLE, waiting
for work.
) = 85
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] futex_time64(0x8009aee2, FUTEX_WAIT_PRIVATE, 1, NULL) = -1
EINVAL (Invalid argument)
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] futex_time64(0x8009aee2, FUTEX_WAIT_PRIVATE, 1, NULL) = -1
EINVAL (Invalid argument)
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] futex_time64(0x8009aee2, FUTEX_WAIT_PRIVATE, 1, NULL) = -1
EINVAL (Invalid argument)
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] futex_time64(0x8009aee2, FUTEX_WAIT_PRIVATE, 1, NULL) = -1
EINVAL (Invalid argument)
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] futex_time64(0x8009aee2, FUTEX_WAIT_PRIVATE, 1, NULL) = -1
EINVAL (Invalid argument)
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] futex_time64(0x8009aee2, FUTEX_WAIT_PRIVATE, 1, NULL) = -1
EINVAL (Invalid argument)

Interestingly, a simple test program [2] works fine under similar
conditions.

I tried to dig and debug, but I can't find out what is the root cause and I
suppose it can occur elsewhere, for another program...

Hi there,

I have a quite complex issue, with uclibc-ng. Here is a summary.
Tested with qemu (buildroot for q800) on the m68k architecture, rsyslog
consumes 100% CPU during its pthread_cond_wait() calls.
This is in [1] in the doIdleProcessing() function.

Using glibc+m68k does not reveal this issue, and uclibc-ng on arm doesn't
either.

Strace output shows that the futex_time64() syscall is repeatedly returning
EINVAL, indicating that the call is looping without proper blocking:
# strace -f rsyslogd -dn
<snip>
[pid   110] write(1, "9139.913444393:main Q:Reg/w0  : "...,
859139.913444393:main Q:Reg/w0  : wti.c: main Q:Reg/w0: worker IDLE, waiting
for work.
) = 85
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] futex_time64(0x8009aee2, FUTEX_WAIT_PRIVATE, 1, NULL) = -1
EINVAL (Invalid argument)
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] futex_time64(0x8009aee2, FUTEX_WAIT_PRIVATE, 1, NULL) = -1
EINVAL (Invalid argument)
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] futex_time64(0x8009aee2, FUTEX_WAIT_PRIVATE, 1, NULL) = -1
EINVAL (Invalid argument)
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] futex_time64(0x8009aee2, FUTEX_WAIT_PRIVATE, 1, NULL) = -1
EINVAL (Invalid argument)
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] futex_time64(0x8009aee2, FUTEX_WAIT_PRIVATE, 1, NULL) = -1
EINVAL (Invalid argument)
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] get_thread_area()           = 0xc0b73970
[pid   110] futex_time64(0x8009aee2, FUTEX_WAIT_PRIVATE, 1, NULL) = -1
EINVAL (Invalid argument)

Interestingly, a simple test program [2] works fine under similar
conditions.

I tried to dig and debug, but I can't find out what is the root cause and I
suppose it can occur elsewhere, for another program...

Any help or suggestions would be appreciated!

[1]: https://github.com/rsyslog/rsyslog/blob/master/runtime/wti.c#L362
[2]: https://www.geeksforgeeks.org/condition-wait-signal-multi-threading/

Thanks !
JM
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