Messages in this thread | | | Subject | Re: [PATCH 01/23] tref: Implement task references. | From | (Eric W. Biederman) | Date | Fri, 03 Mar 2006 10:48:05 -0700 |
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Oleg Nesterov <oleg@tv-sign.ru> writes:
> Eric W. Biederman wrote: >> >> Oleg Nesterov <oleg@tv-sign.ru> writes: >> >> > I think there is another, much simpler solution. We can make a "reference" > to >> > the >> > pid itself to protect it against free_pidmap(), so that this pid can't be >> > reused. >> >> However with my trivial hostile program I can with 32 or 33 living processes >> each with 1000 references to dead processes I can completely saturate the >> default pid map. And it won't be obvious why alloc_pidmap is failing. > > Yes, this is a problem. Please see the new version below. Instead of delaying > pid releasing, free_pidmap() just invalidates pid_ref. The code becomes even > simpler.
And it removes most of my interaction problem with multiple pid spaces.
>> Your resource consumption with the extra hash table is higher than >> mine at until very high process counts. > > The size of ref_array[] could be arbitrary low (we can't use pid_hashfn() in > this case, of course). And tref adds 4 * sizeof(void*) to every task, and it > is much more complicated.
I guess the worst case behavior would be triggered by a find in /proc. Which would probably populate a ref for every pid, and it isn't that uncommon. So I suspect we really want to make ref_array be able to use pid hashfn as it is likely to get an equal amount of use.
More comments when I have time.
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