Messages in this thread | | | Date | Mon, 24 Jul 2006 19:06:26 -0700 | From | Andrew Morton <> | Subject | Re: [RFC] ps command race fix |
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On Tue, 25 Jul 2006 10:53:39 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> On Mon, 24 Jul 2006 18:20:00 -0700 > Andrew Morton <akpm@osdl.org> wrote: > > > > It allocates a potentially-significant amount of memory per-task, until > > that tasks exits (we could release it earlier, but the problem remains) and > > it adds yet another global lock in the process exit path. > > > I see. > > > > 5 files changed, 138 insertions(+), 62 deletions(-) > > > > And it adds complexity and code. > > > > So I think we're still seeking a solution to this. > > > > Options might be: > > > > a) Pin the most-recently-visited task in some manner, so that it is > > still on the global task list when we return. That's fairly simple to > > do (defer the release_task()) but it affects task lifetime and visibility > > in rare and worrisome ways. > > > > b) Change proc_pid_readdir() so that it walks the pid_hash[] array > > instead of the task list. Need to do something clever when traversing > > each bucket's list, but I'm not sure what ;) It's the same problem. > > > > Possibly what we could do here is to permit the task which is walking > > /proc to pin a particular `struct pid': take a ref on it then when we > > next start walking one of the pid_hash[] chains, we _know_ that the > > `struct pid' which we're looking for will still be there. Even if it > > now refers to a departed process. > > > > c) Nuke the pid_hash[], convert the whole thing to a radix-tree. > > They're super-simple to traverse. Not sure what we'd index it by > > though. > > > > I guess b) is best. > > > > I tried b) at the first place.
OK.
> but it was not very good because > proc_pid_readdir() has to traverse all pids, not tgids.
You mean "all tgids, not pids".
> So, I had to access > task_struct of the pid. I wanted to avoid to access task struct itself,
Why do you wish to avoid accessing the task_struct?
> my patch implemented a table made only from tgids. > > But as you say, my patch is much intrusive. > I'll dig this more. thank you for advise.
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