linux-kernel - Re: [RFC PATCH 1/2] Fix: sched/membarrier: p->mm->membarrier

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20190904111126.GB24568@redhat.com>
Date:   Wed, 4 Sep 2019 13:11:27 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Russell King - ARM Linux admin <linux@...linux.org.uk>,
        Chris Metcalf <cmetcalf@...hip.com>,
        Christoph Lameter <cl@...ux.com>,
        Kirill Tkhai <tkhai@...dex.ru>, Mike Galbraith <efault@....de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [RFC PATCH 1/2] Fix: sched/membarrier: p->mm->membarrier_state
 racy load

with or without these changes...

Why do membarrier_register_*_expedited() check get_nr_threads() == 1?
This makes no sense to me, atomic_read(mm_users) == 1 should be enough.

And I am not sure I understand membarrier_mm_sync_core_before_usermode().
OK, membarrier_private_expedited() can race with user -> kernel -> user
transition, but we do not care unless both user's above have the same mm?
Shouldn't membarrier_mm_sync_core_before_usermode() do

	if (current->mm != mm)
		return;

at the start to make it more clear and avoid sync_core_before_usermode()
if possible?

Oleg.