Check value of PF_NO_SETAFFINITY

Question

Is it possible to tell whether a process/thread has the PF_NO_SETAFFINITY flag set? I'm running taskset on a series of process ids and some are throwing errors of the following form:

taskset: failed to set pid 30's affinity: Invalid argument

I believe this is because some processes have PF_NO_SETAFFINITY set (see Answer).

Thank you!

Answer 1

Yes - look at /proc/PID/stat's 'flag' field

<linux/sched.h

#define PF_NO_SETAFFINITY 0x04000000        /* Userland is not allowed to meddle with cpus_allowed */

Look here for details on using /proc:

• http://man7.org/linux/man-pages/man5/proc.5.html
• https://supportcenter.checkpoint.com/supportcenter/portal?eventSubmit_doGoviewsolutiondetails=&solutionid=sk65143

Example:

ps -eaf
www-data 30084 19962  0 07:09 ?        00:00:00 /usr/sbin/apache2 -k start
...

cat /proc/30084/stat
30084 (apache2) S 19962 19962 19962 0 -1 4194624 554 0 3 0 0 0 0 0 20 0 1 0 298837672 509616128 5510 18446744073709551615 1 1 0 0 0 0 0 16781312 201346799 0 0 0 17 0 0 0 0 0 0 0 0 0 0 0 0 0 0

The flags are 4194624

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Q: Do you mind specifying how you'd write a simple script that outputs true/false based on whether you're allowed to set affinity?

A: I don't feel comfortable providing this without the opportunity to test, but you can try something like this...

flags=$(cut -f 9 -d ' ' /proc/30084/stat)
echo $(($flags & 0x40000000))