Linux-kselftest Archive on lore.kernel.org
 help / color / Atom feed
From: Suren Baghdasaryan <surenb@google.com>
To: "Michal Koutný" <mkoutny@suse.com>
Cc: cgroups mailinglist <cgroups@vger.kernel.org>,
	alex.shi@linux.alibaba.com, Roman Gushchin <guro@fb.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	kernel-team <kernel-team@android.com>,
	JeiFeng Lee <linger.lee@mediatek.com>,
	linux-arm-kernel@lists.infradead.org,
	LKML <linux-kernel@vger.kernel.org>,
	linux-kselftest@vger.kernel.org,
	linux-mediatek@lists.infradead.org, Li Zefan <lizefan@huawei.com>,
	matthias.bgg@gmail.com, shuah@kernel.org,
	Tejun Heo <tj@kernel.org>, Tom Cherry <tomcherry@google.com>
Subject: Re: [PATCH v2 1/3] cgroup: Iterate tasks that did not finish do_exit()
Date: Fri, 24 Jan 2020 14:56:51 -0800
Message-ID: <CAJuCfpGjC=YwY=oNnYFNDp2nCuR9YhSU95=xbbeoDEheemte+Q@mail.gmail.com> (raw)
In-Reply-To: <20200124114017.8363-2-mkoutny@suse.com>

On Fri, Jan 24, 2020 at 3:40 AM Michal Koutný <mkoutny@suse.com> wrote:
>
> PF_EXITING is set earlier than actual removal from css_set when a task
> is exitting. This can confuse cgroup.procs readers who see no PF_EXITING
> tasks, however, rmdir is checking against css_set membership so it can
> transitionally fail with EBUSY.
>
> Fix this by listing tasks that weren't unlinked from css_set active
> lists.
> It may happen that other users of the task iterator (without
> CSS_TASK_ITER_PROCS) spot a PF_EXITING task before cgroup_exit(). This
> is equal to the state before commit c03cd7738a83 ("cgroup: Include dying
> leaders with live threads in PROCS iterations") but it may be reviewed
> later.
>
> Reported-by: Suren Baghdasaryan <surenb@google.com>
> Fixes: c03cd7738a83 ("cgroup: Include dying leaders with live threads in PROCS iterations")
> Signed-off-by: Michal Koutný <mkoutny@suse.com>
> ---
>  include/linux/cgroup.h |  1 +
>  kernel/cgroup/cgroup.c | 23 ++++++++++++++++-------
>  2 files changed, 17 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index d7ddebd0cdec..e75d2191226b 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -62,6 +62,7 @@ struct css_task_iter {
>         struct list_head                *mg_tasks_head;
>         struct list_head                *dying_tasks_head;
>
> +       struct list_head                *cur_tasks_head;
>         struct css_set                  *cur_cset;
>         struct css_set                  *cur_dcset;
>         struct task_struct              *cur_task;
> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> index 735af8f15f95..a6e3619e013b 100644
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -4404,12 +4404,16 @@ static void css_task_iter_advance_css_set(struct css_task_iter *it)
>                 }
>         } while (!css_set_populated(cset) && list_empty(&cset->dying_tasks));
>
> -       if (!list_empty(&cset->tasks))
> +       if (!list_empty(&cset->tasks)) {
>                 it->task_pos = cset->tasks.next;
> -       else if (!list_empty(&cset->mg_tasks))
> +               it->cur_tasks_head = &cset->tasks;
> +       } else if (!list_empty(&cset->mg_tasks)) {
>                 it->task_pos = cset->mg_tasks.next;
> -       else
> +               it->cur_tasks_head = &cset->mg_tasks;
> +       } else {
>                 it->task_pos = cset->dying_tasks.next;
> +               it->cur_tasks_head = &cset->dying_tasks;
> +       }
>
>         it->tasks_head = &cset->tasks;
>         it->mg_tasks_head = &cset->mg_tasks;
> @@ -4467,10 +4471,14 @@ static void css_task_iter_advance(struct css_task_iter *it)
>                 else
>                         it->task_pos = it->task_pos->next;
>
> -               if (it->task_pos == it->tasks_head)
> +               if (it->task_pos == it->tasks_head) {
>                         it->task_pos = it->mg_tasks_head->next;
> -               if (it->task_pos == it->mg_tasks_head)
> +                       it->cur_tasks_head = it->mg_tasks_head;
> +               }
> +               if (it->task_pos == it->mg_tasks_head) {
>                         it->task_pos = it->dying_tasks_head->next;
> +                       it->cur_tasks_head = it->dying_tasks_head;
> +               }
>                 if (it->task_pos == it->dying_tasks_head)
>                         css_task_iter_advance_css_set(it);
>         } else {
> @@ -4489,11 +4497,12 @@ static void css_task_iter_advance(struct css_task_iter *it)
>                         goto repeat;
>
>                 /* and dying leaders w/o live member threads */
> -               if (!atomic_read(&task->signal->live))
> +               if (it->cur_tasks_head == it->dying_tasks_head &&
> +                   !atomic_read(&task->signal->live))
>                         goto repeat;
>         } else {
>                 /* skip all dying ones */
> -               if (task->flags & PF_EXITING)
> +               if (it->cur_tasks_head == it->dying_tasks_head)
>                         goto repeat;
>         }
>  }
> --
> 2.24.1
>

Tested-by: Suren Baghdasaryan <surenb@google.com>

Thanks!

  reply index

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-16  4:36 [PATCH 1/2] cgroup: allow deletion of cgroups containing only dying processes Suren Baghdasaryan
2020-01-16  4:36 ` [PATCH 2/2] kselftest/cgroup: add cgroup destruction test Suren Baghdasaryan
2020-01-17 15:15 ` [PATCH 0/3] cgroup: Iterate tasks that did not finish do_exit() Michal Koutný
2020-01-17 15:15   ` [PATCH 1/3] cgroup: Unify css_set task lists Michal Koutný
2020-01-17 16:59     ` Tejun Heo
2020-01-17 15:15   ` [PATCH 2/3] cgroup: Iterate tasks that did not finish do_exit() Michal Koutný
2020-01-17 17:28     ` Tejun Heo
2020-01-17 18:41       ` Suren Baghdasaryan
2020-01-20 14:56         ` Michal Koutný
2020-01-24 11:40           ` [PATCH v2 0/3] " Michal Koutný
2020-01-24 11:40             ` [PATCH v2 1/3] " Michal Koutný
2020-01-24 22:56               ` Suren Baghdasaryan [this message]
2020-02-05 17:27                 ` Suren Baghdasaryan
2020-02-12 22:03               ` Tejun Heo
2020-01-24 11:40             ` [PATCH v2 2/3] cgroup: Clean up css_set task traversal Michal Koutný
2020-01-24 11:40             ` [PATCH v2 3/3] kselftest/cgroup: add cgroup destruction test Michal Koutný
2020-02-12 22:10               ` Tejun Heo
2020-01-17 15:15   ` [PATCH " Michal Koutný
2020-01-17 17:30   ` [PATCH 0/3] cgroup: Iterate tasks that did not finish do_exit() Suren Baghdasaryan

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CAJuCfpGjC=YwY=oNnYFNDp2nCuR9YhSU95=xbbeoDEheemte+Q@mail.gmail.com' \
    --to=surenb@google.com \
    --cc=alex.shi@linux.alibaba.com \
    --cc=cgroups@vger.kernel.org \
    --cc=guro@fb.com \
    --cc=hannes@cmpxchg.org \
    --cc=kernel-team@android.com \
    --cc=linger.lee@mediatek.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-kselftest@vger.kernel.org \
    --cc=linux-mediatek@lists.infradead.org \
    --cc=lizefan@huawei.com \
    --cc=matthias.bgg@gmail.com \
    --cc=mkoutny@suse.com \
    --cc=shuah@kernel.org \
    --cc=tj@kernel.org \
    --cc=tomcherry@google.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-kselftest Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-kselftest/0 linux-kselftest/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-kselftest linux-kselftest/ https://lore.kernel.org/linux-kselftest \
		linux-kselftest@vger.kernel.org
	public-inbox-index linux-kselftest

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kselftest


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git