lkml.org 
[lkml]   [2023]   [Aug]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 0/2] introduce __next_thread(), change next_thread()
    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.

    \
     
     \ /
      Last update: 2023-08-24 17:50    [W:3.203 / U:0.168 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site