From: "Eric W. Biederman" <ebiederm@xmission.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Christian Brauner <brauner@kernel.org>, Tejun Heo <tj@kernel.org>,
Petr Mladek <pmladek@suse.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Michal Hocko <mhocko@suse.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Oleg Nesterov <oleg@redhat.com>
Subject: Re: re. Spurious wakeup on a newly created kthread
Date: Sat, 25 Jun 2022 19:21:50 -0500 [thread overview]
Message-ID: <87sfnsw9y9.fsf@email.froward.int.ebiederm.org> (raw)
In-Reply-To: <CAHk-=wiutNT47oNhyk_WvMj2qp4pehYFptXCUzW=u_2STLQiww@mail.gmail.com> (Linus Torvalds's message of "Sat, 25 Jun 2022 16:43:39 -0700")
Linus Torvalds <torvalds@linux-foundation.org> writes:
> On Sat, Jun 25, 2022 at 4:28 PM Eric W. Biederman <ebiederm@xmission.com> wrote:
>>
>> I presume you mean kthreadd games?
>
> Yeah, sorry.
>
>> So with the introduction of kthreadd the kernel threads were moved
>> out of the userspace process tree, and userspace stopped being able to
>> influence the kernel threads.
>
> Ahh. So essentially it's indeed just basically the parenting issue.
That is one way to look at it. The way I described it at the time was:
> commit 73c279927f89561ecb45b2dfdf9314bafcfd9f67
> Author: Eric W. Biederman <ebiederm@xmission.com>
> Date: Wed May 9 02:34:32 2007 -0700
>
> kthread: don't depend on work queues
>
> Currently there is a circular reference between work queue initialization
> and kthread initialization. This prevents the kthread infrastructure from
> initializing until after work queues have been initialized.
>
> We want the properties of tasks created with kthread_create to be as close
> as possible to the init_task and to not be contaminated by user processes.
> The later we start our kthreadd that creates these tasks the harder it is
> to avoid contamination from user processes and the more of a mess we have
> to clean up because the defaults have changed on us.
>
> So this patch modifies the kthread support to not use work queues but to
> instead use a simple list of structures, and to have kthreadd start from
> init_task immediately after our kernel thread that execs /sbin/init.
>
> By being a true child of init_task we only have to change those process
> settings that we want to have different from init_task, such as our process
> name, the cpus that are allowed, blocking all signals and setting SIGCHLD
> to SIG_IGN so that all of our children are reaped automatically.
>
> By being a true child of init_task we also naturally get our ppid set to 0
> and do not wind up as a child of PID == 1. Ensuring that tasks generated
> by kthread_create will not slow down the functioning of the wait family of
> functions.
>
> [akpm@linux-foundation.org: use interruptible sleeps]
> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
> Cc: Oleg Nesterov <oleg@tv-sign.ru>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Eric
next prev parent reply other threads:[~2022-06-26 0:22 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-22 14:08 [PATCH] workqueue: Make create_worker() safe against spurious wakeups Petr Mladek
2022-06-23 7:00 ` Petr Mladek
2022-06-23 7:14 ` Michal Hocko
2022-06-25 5:00 ` re. Spurious wakeup on a newly created kthread Tejun Heo
2022-06-25 17:01 ` Linus Torvalds
2022-06-25 17:36 ` Eric W. Biederman
2022-06-25 18:25 ` Linus Torvalds
2022-06-25 18:43 ` Linus Torvalds
2022-06-25 23:28 ` Eric W. Biederman
2022-06-25 23:41 ` Eric W. Biederman
2022-06-25 23:43 ` Linus Torvalds
2022-06-25 23:48 ` Linus Torvalds
2022-06-26 0:19 ` Eric W. Biederman
2022-06-27 0:01 ` Wedson Almeida Filho
2022-06-27 7:11 ` Peter Zijlstra
2022-06-27 18:23 ` Wedson Almeida Filho
2022-06-27 18:45 ` Linus Torvalds
2022-06-26 19:14 ` [PATCH 0/3] kthread: Stop using TASK_UNINTERRUPTIBLE Eric W. Biederman
2022-06-26 19:15 ` [PATCH 1/3] kthread: Remove the flags argument from kernel_thread Eric W. Biederman
2022-06-26 21:20 ` Linus Torvalds
2022-06-26 19:16 ` [PATCH 2/3] kthread: Replace kernel_thread with new_kthread Eric W. Biederman
2022-06-26 19:16 ` [PATCH 3/3] kthread: Stop abusing TASK_UNINTERRUPTIBLE (INCOMPLETE) Eric W. Biederman
2022-06-26 19:59 ` Linus Torvalds
2022-06-26 20:23 ` Tejun Heo
2022-06-26 20:55 ` Linus Torvalds
2022-06-27 7:22 ` Peter Zijlstra
2022-06-27 8:11 ` Tejun Heo
2022-06-27 18:04 ` Wedson Almeida Filho
2022-06-27 22:06 ` Peter Zijlstra
2022-06-27 22:34 ` Linus Torvalds
2022-06-27 22:45 ` Wedson Almeida Filho
2022-06-28 0:32 ` Wedson Almeida Filho
2022-06-28 7:58 ` Peter Zijlstra
2022-06-30 0:57 ` Wedson Almeida Filho
2022-06-26 22:14 ` kernel test robot
2022-06-26 22:34 ` kernel test robot
2022-06-26 0:21 ` Eric W. Biederman [this message]
2022-06-28 14:16 ` re. Spurious wakeup on a newly created kthread Christian Brauner
2022-06-26 0:26 ` Eric W. Biederman
2022-06-26 1:58 ` Tejun Heo
2022-06-26 2:53 ` Linus Torvalds
2022-06-26 6:09 ` Tejun Heo
2022-06-27 12:04 ` Michal Hocko
2022-06-28 9:51 ` Petr Mladek
2022-06-28 10:07 ` Tejun Heo
2022-06-27 8:07 ` Michal Hocko
2022-06-27 8:21 ` Tejun Heo
2022-06-27 10:18 ` Michal Hocko
2022-06-28 15:08 ` Petr Mladek
2022-08-04 8:57 ` [PATCH] workqueue: Make create_worker() safe against spurious wakeups Lai Jiangshan
2022-08-04 10:19 ` Lai Jiangshan
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