Messages in this thread | | | From | (Eric W. Biederman) | Subject | Re: [PATCH] Mark timer_stats as incompatible with multiple pid namespaces | Date | Thu, 13 Dec 2007 04:55:22 -0700 |
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Ingo Molnar <mingo@elte.hu> writes:
> * Eric W. Biederman <ebiederm@xmission.com> wrote: > >> /proc/timer_stats currently reports the user of a timer by pid, which >> is a reasonable approach. However if you are not in the initial pid >> namespace the pid that is reported is nonsense. >> >> Therefore until we can make timer_stats pid namespace safe just >> disable it in the build if pid namespace support is selected so we at >> least know we have a conflict. > > What the heck??? Please solve this properly instead of hiding it. > /proc/timer_stats is damn useful and it's a must-have for powertop to > work.
Hmm. Perhaps the dependency conflict should go in the other direction then.
My goal is to document the issue while a proper fix is being written. I have known about this for all of about 1 day now. It was added since last time I went through the kernel and made a thorough sweep of pid users.
What the proper fix is isn't even obvious at this point. Possibly it is making /proc/timer_stats disappear in child pid namespaces. Which we don't currently have the infrastructure fore. Possibly it is reworking the stats collection so we store a struct pid * instead of a pid_t value. So we would know if the reader of the value can even see processes you have collected stats for.
It is going to take a bit to digest what is going on and solve this properly.
In the same vein do we actively have interesting user space programs using /proc/sched_debug? It is the same class of problem. Yet another interface talking to user space with pids.
Eric
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