Messages in this thread | | | From | (Eric W. Biederman) | Subject | Re: [PATCH] task_pid_nr_ns() breaks proc_pid_readdir() | Date | Mon, 19 Nov 2007 11:15:03 -0700 |
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Oleg Nesterov <oleg@tv-sign.ru> writes:
> On 11/17, Eric W. Biederman wrote: >> >> Oleg Nesterov <oleg@tv-sign.ru> writes: >> >> > Make sure that task_pid_nr_ns() returns !0 before updating tgid. Note that >> > next_tgid(tgid + 1) can find the same "struct pid" again, but we shouldn't >> > go into the endless loop because pid_task(PIDTYPE_PID) must return NULL in >> > this case, so next_tgid() can't return the same task. >> > >> Oleg I think I would rather update next_tgid to return the tgid (which >> removes the need to call task_pid_nr_ns). This keeps all of the task >> iteration logic together in next_tgid. > > Yes sure, I think your patch is also correct, please use it. > > <offtopic> > > Personally, I hate the functions which use pointers to return another value. > (yes, yes, I know, my taste is perverted). Why don't we return structure in > this case? We can even make a common helper struct, say, > > Of course, another option is to rewrite the kernle in perl, in that case > proc_pid_readdir() can just do > > (task, tgid) = next_tgid();
I wish that last syntax worked in C. That would make returning structures so much easier. From a compiler optimization standpoint returning structures is ever so much nicer. Seeing through pointers or references to optimize things is tricky.
> </offtopic> > >> Although looking at this in more detail, I'm half wondering if >> proc_pid_make_inode() should take a struct pid instead of a task. > > Yes, I also thought about this. Needs more changes, and still not perfect. > > I am starting to think we need a more generic change. How about the patch > below? With this change the stable task_struct implies we have the stable > pids, this allows us to do a lot of cleanups.
I don't see the huge pile of opportunities to clean up. But otherwise I am in favor of it. In the normal case it should only delay freeing of struct pid (and the corresponding namespace) by an rcu interval so it isn't a big deal.
I suspect it will be a help with killing things like the global pids in task_struct.
Regardless I'm going to pass on the keeping struct pid on the task struct until we free it and reference counting it there for the immediate present as I think we can solve the immediate issues cleanly without it, and we are pretty much in bug fixing territory now.
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