Re: [PATCH] Re: [RFC PATCH] namespaces: fix leak on fork() failure

[Eric W. Biederman]

Mike Galbraith <efault@xxxxxx> writes:

> On Fri, 2012-05-04 at 08:36 -0700, Eric W. Biederman wrote: 
>> Mike Galbraith <efault@xxxxxx> writes:
>> 
>> > On Fri, 2012-05-04 at 07:13 -0700, Eric W. Biederman wrote: 
>> >> Mike Galbraith <efault@xxxxxx> writes:
>> 
>> >> Did you have HZ=100 in that kernel?  400 tasks at 100Hz all serialized
>> >> somehow and then doing synchronize_rcu at a jiffy each would account
>> >> for 4 seconds.  And the nsproxy certainly has a synchronize_rcu call.
>> >
>> > HZ=250
>> 
>> Rats.  Then non of my theories even approaches holding water.
>> 
>> >> The network namespace is comparatively heavy weight, at least in the
>> >> amount of code and other things it has to go through, so that would be
>> >> my prime suspect for those 29 seconds.  There are 2-4 synchronize_rcu
>> >> calls needed to put the loopback device.  Still we use
>> >> synchronize_rcu_expedited and that work should be out of line and all of
>> >> those calls should batch.
>> >> 
>> >> Mike is this something you are looking at a pursuing farther?
>> >
>> > Not really, but I can put it on my good intentions list.
>> 
>> About what I expected.  I just wanted to make certain I understood the
>> situation.
>> 
>> I will remember this as something weird and when I have time perhaps
>> I will investigate and track it.
>> 
>> >> I want to guess the serialization comes from waiting on children to be
>> >> reaped but the namespaces are all cleaned up in exit_notify() called
>> >> from do_exit() so that theory doesn't hold water.  The worst case
>> >> I can see is detach_pid from exit_signal running under the task list lock.
>> >> but nothing sleeps under that lock.  :(
>> >
>> > I'm up to my ears in zombies with several instances of the testcase
>> > running in parallel, so I imagine it's the same with hackbench.
>> 
>> Oh interesting.
>> 
>> > marge:/usr/local/tmp/starvation # taskset -c 3 ./hackbench -namespace& for i in 1 2 3 4 5 6 7 ; do ps ax|grep defunct|wc -l;sleep 1; done
>> > [1] 29985
>> > Running with 10*40 (== 400) tasks.
>> > 1
>> > 397
>> > 327
>> > 261
>> > 199
>> > 135
>> > 72
>> > marge:/usr/local/tmp/starvation # Time: 7.675
>> 
>> So if I read your output right the first second is spent running the
>> code and the rest of the time is spent reaping zombies.
>
> The distance between these is mighty fishy.

Yes.  1 to 2 jiffiers per iteration.

That probably puts us in:
do_wait()
   do_wait_thread()
      wait_consider_task()
         wait_task_zombie()
            release_task()

The only parts that I see that are clearly outside of the tasklist_lock are:
put_user in wait_task_zombie 
proc_flush_task in release_task
release_thread in release_task

Of those if I had to take a blind guess I would guess something in
proc_flush_task possibly kern_unmount.  That is the only bit that
should be namespace unique.

But shrug.  I have looked and I don't see anything obvious in those
code paths.

The only other possibility are schedule and signal deliver in the
syscall return path.  Perhaps there is kernel thread or a work queue
or something running on the same cpu and using all of the time and
our reaper thread only gets scheduled occasionally.  Or perhaps
it is something peculiar with the signal delivery logic.

Shrug.  I have skimmed through all of that code and I don't see anything
obvious.  I guess it would take a few more data points to figure out
where we are sleeping for a jiffy or two while we are reaping children.

Eric

> marge:~ # grep 'signalfd_cleanup ' /trace2
>           vsftpd-9628  [003] ....   712.571961: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.575717: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.579698: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.587734: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.591671: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.595695: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.599685: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.603680: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.607682: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.611692: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.615740: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.619705: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.623730: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.627748: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.631712: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.635741: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.643683: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.647685: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.651691: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.655742: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.659738: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.663738: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.667756: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.671693: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.679682: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.683694: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.687750: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.691738: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.695751: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.699740: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.703736: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.707757: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.711685: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.715689: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.719694: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.723742: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.727752: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.731695: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.739687: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.743688: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.747697: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.751689: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.755688: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.759699: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.763705: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.767754: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.771702: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.775749: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.775884: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.783754: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.787754: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.791763: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.795764: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.799755: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.807768: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.835723: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.843695: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.847752: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.851694: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.855711: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.859704: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.863751: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.867754: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.871753: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.875765: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.879706: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.883696: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.887697: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.891711: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.898493: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.911740: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.927755: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.955754: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.975771: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   712.995826: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.003739: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.003920: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.011710: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.015831: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.023827: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.031694: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.035715: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.039714: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.043816: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.047726: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.051818: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.055724: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.059814: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.063725: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.067824: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.071825: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.075726: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.079709: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.083814: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.087850: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.095859: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.099826: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.103830: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.107726: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.111723: signalfd_cleanup <-__cleanup_sighand
>           vsftpd-9628  [003] d...   713.115874: signalfd_cleanup <-__cleanup_sighand
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