linux-kernel - Re: [PATCH v2 3/5] exec: Move cleanup of posix timers on exec out of de

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Date:   Mon, 9 Mar 2020 21:17:29 +0100
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Bernd Edlinger <bernd.edlinger@...mail.de>,
        Kees Cook <keescook@...omium.org>,
        Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Oleg Nesterov <oleg@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Andrei Vagin <avagin@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Yuyang Du <duyuyang@...il.com>,
        David Hildenbrand <david@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Anshuman Khandual <anshuman.khandual@....com>,
        David Howells <dhowells@...hat.com>,
        James Morris <jamorris@...ux.microsoft.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Christian Kellner <christian@...lner.me>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Aleksa Sarai <cyphar@...har.com>,
        "Dmitry V. Levin" <ldv@...linux.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>
Subject: Re: [PATCH v2 3/5] exec: Move cleanup of posix timers on exec out of
 de_thread

On Mon, Mar 09, 2020 at 03:06:46PM -0500, Eric W. Biederman wrote:
> Christian Brauner <christian.brauner@...ntu.com> writes:
> 
> > On Sun, Mar 08, 2020 at 04:36:55PM -0500, Eric W. Biederman wrote:
> >> 
> >> These functions have very little to do with de_thread move them out
> >> of de_thread an into flush_old_exec proper so it can be more clearly
> >> seen what flush_old_exec is doing.
> >> 
> >> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> >> ---
> >>  fs/exec.c | 10 +++++-----
> >>  1 file changed, 5 insertions(+), 5 deletions(-)
> >> 
> >> diff --git a/fs/exec.c b/fs/exec.c
> >> index ff74b9a74d34..215d86f77b63 100644
> >> --- a/fs/exec.c
> >> +++ b/fs/exec.c
> >> @@ -1189,11 +1189,6 @@ static int de_thread(struct task_struct *tsk)
> >
> > While you're cleaning up de_thread() wouldn't it be good to also take
> > the opportunity and remove the task argument from de_thread(). It's only
> > ever used with current. Could be done in one of your patches or as a
> > separate patch.
> 
> How does that affect the code generation?

The same way renaming "tsk" to "me" does.

> 
> My sense is that computing current once in flush_old_exec is much
> better than computing it in each function flush_old_exec calls.
> I remember that computing current used to be not expensive but
> noticable.
> 
> For clarity I can see renaming tsk to me.  So that it is clear we are
> talking about the current process, and not some arbitrary process.

For clarity since de_thread() uses "tsk" giving the impression that any
task can be dethreaded while it's only ever used with current. It's just
a suggestion since you're doing the rename tsk->me anyway it would fit
with the series. You do whatever you want though.
(I just remember that the same request was made once to changes I did:
Don't pass current as arg when it's the only task passed.)