Kernel porting ERRORs Failed setting process group of NNN to 0/1; add_tid_to_cgroup failed

[failuch]

Hello all,

I saw that a lot of people encountered these error :

• W/ActivityManager(  349): Failed setting process group of 4911 to 0
• W/SchedPolicy(  349): add_tid_to_cgroup failed to write '4911' (Permission denie
• d); background=1

And I was unable to find explanation/solution  for this problem, although

I have checked  cgroups are mounted and /dev/cpuctl/tasks exist

Can you please to comment ?


ThX

[Glenn Kasten]

Sometimes this is caused by incorrect init.rc.  Make sure your init.rc has all of the latest changes from system/core/rootdir/init.rc especially if you have forked it.

You mentioned a "lot of people" have seen this .. were these on other external postings or bug reports? if so can you please supply a link to these, it will help diagnose to see the other reports. 

[Glenn Kasten]

I suggest getting a stack trace at the time of log, to see what is happening.

For example at that ALOGE also log the tid and fd, and then do an abort() or *(char*) 0 = 0;

This will prevent the system from running of course, but a logcat during bootup should show why it's failing.

On Wednesday, October 3, 2012 2:10:48 PM UTC-7, John Tapsell wrote:

Hi Glenn,

  Can you give any more hints about what to look for in init.rc ?  The cgroups code is exactly the same in my init.rc

  I have:

> ls -l /dev/cpuctl/tasks

-rwxrwxrwx system   system          0 2000-01-01 00:23 tasks

Yet I still get:

W/SchedPolicy(  189): add_tid_to_cgroup failed to write '435' (Permission denied); background=0

etc.

Any ideas please?

John

[John Tapsell]

Thanks for the help Glenn - I now have more details.

The process triggering the warning is system_server, and this is running as user "system".

It is trying to write the pid of various other processes (com.android.inputmethod.latin, com.android.phone. com.android.launcher, etc) into /dev/inputctl/tasks

But these other processes have a different uid (they run as user app_16, app_20, radio, etc)

So the kernel/cgroups.c  file does:

                if (cred->euid &&
                    cred->euid != tcred->uid &&
                    cred->euid != tcred->suid) {
                        rcu_read_unlock();
                        cgroup_unlock();
                        return -EACCES;
                }

It fails on the uid check, and returns an error.  (I put a printk here to confirm this, and confirm the difference in euid and uid)

Is system_server supposed to be running as user "system", and is it supposed to be trying to change the cgroup of process owned by another user?

Thanks,

John

[Glenn Kasten]

Your version of the source code appears to be missing this commit

commit 4a12178d3dd5b06a215076c60dc7cb124d711373

    cgroup: Add generic cgroup subsystem permission checks

You may be looking at a branch which lacks Android patches.