[Bug 248537] procstat -e/kvm_getenvv() fails for specific processes

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=248537

            Bug ID: 248537
           Summary: procstat -e/kvm_getenvv() fails for specific processes
           Product: Base System
           Version: 12.1-RELEASE
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: bugs at FreeBSD.org
          Reporter: ag-freebsd at muc.de

While implementing *BSD platform support for sysutils/py-psutils, I've
encountered strange behaviour when using either the libprocstat or kvm
interface to retrieve the environ for a foreign process on the system:

Both kvm_getenvv() and procstat_getenvv() return ENOMEM on some systems.

This happens repeatingly reproducable e.g. for the X11 Xorg server process; it
can already be seen by using system utilities as well:

» pgrep Xorg
1401

» sudo ps -e -p 1401
 PID TT  STAT      TIME COMMAND
1401 v0  S    646:37.30  /usr/local/bin/Xorg :0 -listen tcp
 (shows no environment and swallows the error)

» sudo procstat -e 1401
  PID COMM             ENVIRONMENT
procstat: sysctl(kern.proc.env): Cannot allocate memory
 1401 Xorg             -


I've tried to track this down and searched for similar bug reports, but all
suggestions mentioned there do not work.

1) Both library functions internally use the sysctl() interface to retrieve the
information from the kernel. sysctl() uses _locked memory_ for transferring the
data. So, a resource limit may be hit.

But even if I raise the locked memory soft and hard limits (``ulimit -l -H
...´´, the error stays.


2) Even if I raise **vm.max_wired** to make sure no global limit is reached,
the error stays.


There is another scenario which trigges the problem:
When using the 'Cirrus CI'  continuous build platform (which runs on Google
compute engine to my knownledge), there is also a process whose environment
cannot be retrieve with the system interfaces kvm_getenvv() /
procstat_getenvv():

sysctl vm.max_wired vm.stats.vm.v_wire_count
vm.max_wired: 331490
vm.stats.vm.v_wire_count: 136164

limits
Resource limits (current):
  cputime              infinity secs
  filesize             infinity kB
  datasize             33554432 kB
  stacksize              524288 kB
  coredumpsize         infinity kB
  memoryuse            infinity kB
  memorylocked           131072 kB
  maxprocesses             8499
  openfiles              116856
  sbsize               infinity bytes
  vmemoryuse           infinity kB
  pseudo-terminals     infinity
  swapuse              infinity kB
  kqueues              infinity
  umtxp                infinity

ps auxm
USER    PID  %CPU %MEM    VSZ    RSS TT  STAT STARTED     TIME COMMAND
root  25598   0.0  7.0 990596 291548 u0  S+   23:58    0:12.63
./cirrus-ci-agent -task-id 5900109814693888 -client-token
d5950e87a4cc4ce89436b07589944d60 -server-token abae919382e6411787e4d67fc60dd527
-api-endpoint grpc.cirrus-ci.com:443
root      1   0.0  0.0   9788    284  -  ILs  23:52    0:00.01 /sbin/init --
root    453   0.0  0.0  10456   1460  -  Ss   23:52    0:00.00 /sbin/devd
[....]
root     22   0.0  0.0  12320   1596 u0  Is+  23:52    0:00.04 sh /etc/rc
autoboot
root  25548   0.0  0.0  12320   1848 u0  I+   23:58    0:00.00 sh /etc/rc
autoboot
[....]
root      0   0.0  0.0      0    320  -  DLs  23:52    0:00.00 [kernel]
[....]

procstat -e 22
procstat: sysctl(kern.proc.env): Cannot allocate memory
  PID COMM             ENVIRONMENT
   22 sh               -

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