From: Kirill Tkhai <ktkhai@virtuozzo.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Andrea Parri <andrea.parri@amarulasolutions.com>,
akpm@linux-foundation.org, oleg@redhat.com,
viro@zeniv.linux.org.uk, mingo@kernel.org,
paulmck@linux.vnet.ibm.com, keescook@chromium.org,
riel@redhat.com, mhocko@suse.com, tglx@linutronix.de,
kirill.shutemov@linux.intel.com, marcos.souza.org@gmail.com,
hoeun.ryu@gmail.com, pasha.tatashin@oracle.com,
gs051095@gmail.com, ebiederm@xmission.com, dhowells@redhat.com,
rppt@linux.vnet.ibm.com, linux-kernel@vger.kernel.org,
Alan Stern <stern@rowland.harvard.edu>,
Will Deacon <will.deacon@arm.com>,
Boqun Feng <boqun.feng@gmail.com>
Subject: Re: [PATCH 4/4] exit: Lockless iteration over task list in mm_update_next_owner()
Date: Thu, 26 Apr 2018 19:04:14 +0300 [thread overview]
Message-ID: <bea7d306-9742-10b8-3ef9-2a1594dac3a6@virtuozzo.com> (raw)
In-Reply-To: <20180426152053.GC4082@hirez.programming.kicks-ass.net>
On 26.04.2018 18:20, Peter Zijlstra wrote:
> On Thu, Apr 26, 2018 at 04:52:39PM +0300, Kirill Tkhai wrote:
>>>>
>>>> 1)for_each_process(g) copy_process()
>>>> p->mm = mm
>>>> smp_rmb(); smp_wmb() implied by alloc_pid()
>>>> if (g->flags & PF_KTHREAD) list_add_tail_rcu(&p->tasks, &init_task.tasks)
>>>>
>>>> 2)for_each_thread(g, c) copy_process()
>>>> p->mm = mm
>>>> smp_rmb(); smp_wmb() implied by alloc_pid()
>>>> tmp = READ_ONCE(c->mm) list_add_tail_rcu(&p->thread_node, ...)
>
> For these two; what's the purpose of the smp_rmb()? which loads are
> ordered?
(1) and (2) make visible g->flags and c->mm in case we see process is linked
to the task list.
It seems in mm_update_next_owner() we may see result of list_add_tail_rcu(&p->thread_node, ...),
but p->mm = mm will not be visible.
Hm, also I've dived into list_add_tail_rcu() and it contains smp_wmb(). So, it seems
we do not need the barrier implied by alloc_pid().
Kirill
next prev parent reply other threads:[~2018-04-26 16:04 UTC|newest]
Thread overview: 96+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-26 11:00 [PATCH 0/4] exit: Make unlikely case in mm_update_next_owner() more scalable Kirill Tkhai
2018-04-26 11:00 ` [PATCH 1/4] exit: Move read_unlock() up in mm_update_next_owner() Kirill Tkhai
2018-04-26 15:01 ` Oleg Nesterov
2018-04-26 11:00 ` [PATCH 2/4] exit: Use rcu instead of get_task_struct() " Kirill Tkhai
2018-04-26 11:00 ` [PATCH 3/4] exit: Rename assign_new_owner label " Kirill Tkhai
2018-04-26 11:01 ` [PATCH 4/4] exit: Lockless iteration over task list " Kirill Tkhai
2018-04-26 12:35 ` Andrea Parri
2018-04-26 13:52 ` Kirill Tkhai
2018-04-26 15:20 ` Peter Zijlstra
2018-04-26 15:56 ` Kirill Tkhai
2018-04-26 15:20 ` Peter Zijlstra
2018-04-26 16:04 ` Kirill Tkhai [this message]
2018-04-26 15:29 ` Andrea Parri
2018-04-26 16:11 ` Kirill Tkhai
2018-04-26 13:07 ` [PATCH 0/4] exit: Make unlikely case in mm_update_next_owner() more scalable Michal Hocko
2018-04-26 13:52 ` Oleg Nesterov
2018-04-26 14:07 ` Kirill Tkhai
2018-04-26 15:10 ` Oleg Nesterov
2018-04-26 16:19 ` Eric W. Biederman
2018-04-26 19:28 ` Michal Hocko
2018-04-27 7:08 ` Michal Hocko
2018-04-27 18:05 ` Eric W. Biederman
2018-05-01 17:22 ` Eric W. Biederman
2018-05-01 17:35 ` [RFC][PATCH] memcg: Replace mm->owner with mm->memcg Eric W. Biederman
2018-05-02 8:47 ` Michal Hocko
2018-05-02 13:20 ` Johannes Weiner
2018-05-02 14:05 ` Eric W. Biederman
2018-05-02 19:21 ` [PATCH] " Eric W. Biederman
2018-05-02 21:04 ` Andrew Morton
2018-05-02 21:35 ` Eric W. Biederman
2018-05-03 13:33 ` Oleg Nesterov
2018-05-03 14:39 ` Eric W. Biederman
2018-05-04 14:20 ` Oleg Nesterov
2018-05-04 14:36 ` Eric W. Biederman
2018-05-04 14:54 ` Oleg Nesterov
2018-05-04 15:49 ` Eric W. Biederman
2018-05-04 16:22 ` Oleg Nesterov
2018-05-04 16:40 ` Eric W. Biederman
2018-05-04 17:26 ` [PATCH 0/2] mm->owner to mm->memcg fixes Eric W. Biederman
2018-05-04 17:26 ` [PATCH 1/2] memcg: Update the mm->memcg maintenance to work when !CONFIG_MMU Eric W. Biederman
2018-05-04 17:27 ` [PATCH 2/2] memcg: Close the race between migration and installing bprm->mm as mm Eric W. Biederman
2018-05-09 14:51 ` Oleg Nesterov
2018-05-10 3:00 ` Eric W. Biederman
2018-05-10 12:14 ` [PATCH 0/2] mm->owner to mm->memcg fixes Michal Hocko
2018-05-10 12:18 ` Michal Hocko
2018-05-22 12:57 ` Michal Hocko
2018-05-23 19:46 ` Eric W. Biederman
2018-05-24 11:10 ` Michal Hocko
2018-05-24 21:16 ` Andrew Morton
2018-05-24 23:37 ` Andrea Parri
2018-05-30 12:17 ` Michal Hocko
2018-05-31 18:41 ` Eric W. Biederman
2018-06-01 1:57 ` [PATCH] memcg: Replace mm->owner with mm->memcg Eric W. Biederman
2018-06-01 14:52 ` [RFC][PATCH 0/2] memcg: Require every task that uses an mm to migrate together Eric W. Biederman
2018-06-01 14:53 ` [RFC][PATCH 1/2] memcg: Ensure every task that uses an mm is in the same memory cgroup Eric W. Biederman
2018-06-01 16:50 ` Tejun Heo
2018-06-01 18:11 ` Eric W. Biederman
2018-06-01 19:16 ` Tejun Heo
2018-06-04 13:01 ` Michal Hocko
2018-06-04 18:47 ` Tejun Heo
2018-06-04 19:11 ` Eric W. Biederman
2018-06-06 11:13 ` Michal Hocko
2018-06-07 11:42 ` Eric W. Biederman
2018-06-07 12:19 ` Michal Hocko
2018-06-01 14:53 ` [RFC][PATCH 2/2] memcgl: Remove dead code now that all tasks of an mm share a memcg Eric W. Biederman
2018-06-01 14:07 ` [PATCH 0/2] mm->owner to mm->memcg fixes Michal Hocko
2018-05-24 21:17 ` Andrew Morton
2018-05-30 11:52 ` Michal Hocko
2018-05-31 17:43 ` Eric W. Biederman
2018-05-07 14:33 ` [PATCH] memcg: Replace mm->owner with mm->memcg Oleg Nesterov
2018-05-08 3:15 ` Eric W. Biederman
2018-05-09 14:40 ` Oleg Nesterov
2018-05-10 3:09 ` Eric W. Biederman
2018-05-10 4:03 ` [RFC][PATCH] cgroup: Don't mess with tasks in exec Eric W. Biederman
2018-05-10 12:15 ` Oleg Nesterov
2018-05-10 12:35 ` Tejun Heo
2018-05-10 12:38 ` [PATCH] memcg: Replace mm->owner with mm->memcg Oleg Nesterov
2018-05-04 11:07 ` Michal Hocko
2018-05-05 16:54 ` kbuild test robot
2018-05-07 23:18 ` Andrew Morton
2018-05-08 2:17 ` Eric W. Biederman
2018-05-09 21:00 ` Michal Hocko
2018-05-02 23:59 ` [RFC][PATCH] " Balbir Singh
2018-05-03 15:11 ` Eric W. Biederman
2018-05-04 4:59 ` Balbir Singh
2018-05-03 10:52 ` [PATCH 0/4] exit: Make unlikely case in mm_update_next_owner() more scalable Kirill Tkhai
2018-06-01 1:07 ` Eric W. Biederman
2018-06-01 13:57 ` Michal Hocko
2018-06-01 14:32 ` Eric W. Biederman
2018-06-01 15:02 ` Michal Hocko
2018-06-01 15:25 ` Eric W. Biederman
2018-06-04 6:54 ` Michal Hocko
2018-06-04 14:31 ` Eric W. Biederman
2018-06-05 8:15 ` Michal Hocko
2018-06-05 8:48 ` Kirill Tkhai
2018-06-05 15:36 ` Eric W. Biederman
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