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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 4 Dec 2020 12:48:18 -0800
Message-ID: <CAHk-=wgxe-KAqR_y2jP58GthOYKk0YG=6gNxKHxVUJbG7z2CoQ@mail.gmail.com>
Subject: Re: [PATCH 3/3] exec: Transform exec_update_mutex into a rw_semaphore
To:     Bernd Edlinger <bernd.edlinger@hotmail.de>
Cc:     "Eric W. Biederman" <ebiederm@xmission.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
        Jann Horn <jannh@google.com>,
        Vasiliy Kulikov <segoon@openwall.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Oleg Nesterov <oleg@redhat.com>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Sargun Dhillon <sargun@sargun.me>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Waiman Long <longman@redhat.com>,
        Davidlohr Bueso <dave@stgolabs.net>
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On Fri, Dec 4, 2020 at 12:30 PM Bernd Edlinger
<bernd.edlinger@hotmail.de> wrote:
>>
> >    perf_event_open  (exec_update_mutex -> ovl_i_mutex)

Side note: this one looks like it should be easy to fix.

Is there any real reason why exec_update_mutex is actually gotten that
early, and held for that long in the perf event code?

I _think_ we could move the ptrace check to be much later, to _just_ before that

         * This is the point on no return; we cannot fail hereafter.

point in the perf event install chain..

I don't think it needs to be moved down even that much, I think it
would be sufficient to move it down below the "perf_event_alloc()",
but I didn't check very much.

The fact that create_local_trace_uprobe() can end up going into a
lookup of an OVL filesystem path smells kind of odd to me to begin
with, but I didn't look at the whole thing.

PeterZ, is there something I'm missing?

          Linus