Messages in this thread | | | Date | Thu, 24 Aug 2023 17:47:03 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH 0/2] introduce __next_thread(), change next_thread() |
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On 08/24, Linus Torvalds wrote: > > On Thu, 24 Aug 2023 at 07:32, Oleg Nesterov <oleg@redhat.com> wrote: > > > > After document-while_each_thread-change-first_tid-to-use-for_each_thread.patch > > in mm tree + this series > > Looking at your patch 2/2, I started looking at users ("Maybe we > *want* NULL for the end case, and make next_thread() and __next_thread > be the same?").
Yes, but see below.
> One of the main users is while_each_thread(), which certainly wants > that NULL case, both for an easier loop condition,
No. Please note that, say,
do { do_something(t); } while_each_thread(current, t);
differs from for_each_thread() in that it loops starting from current, not current->parent. I guess in most cases the order doesn't matter, and I am going to audit the users and change them to use for_each_thread() when possible.
Or, while_each_thread(current, t) do_something(t);
means do_something for every thread except current. And this have a couple of valid users (say, zap_other_threads), but perhaps we can change them too.
> but also because > the only user that uses the 't' pointer after the loop is > fs/proc/base.c, which wants it to be NULL.
Do you mean first_tid() ? Not only it is the only user that uses the 't' pointer after the loop, it is the only user of lockless while_each_thread() which (in general) is NOT rcu-safe.
But I have already changed it to use for_each_thread(), see https://lore.kernel.org/all/20230823170806.GA11724@redhat.com/
This is document-while_each_thread-change-first_tid-to-use-for_each_thread.patch in mm tree.
> And kernel/bpf/task_iter.c seems to *expect* NULL at the end?
Yes! I think the same and I even documented this in 1/2. To me this code looks simply wrong, but so far I don't understand it enough. Currently I am trying to push the initial cleanups into this code. See the
https://lore.kernel.org/all/20230821150909.GA2431@redhat.com/
thread.
> End result: if you're changing next_thread() anyway, please just > change it to be a completely new thing that returns NULL at the end,
See above.
I'd prefer to audit/change the current users of while_each_thread() and next_thread(), then (perhaps) kill while_each_thread() and/or next_thread().
Oleg.
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