From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sasha Levin Subject: [PATCH AUTOSEL 5.4 02/73] cgroup: Iterate tasks that did not finish do_exit() Date: Wed, 18 Mar 2020 16:52:26 -0400 Message-ID: <20200318205337.16279-2-sashal@kernel.org> References: <20200318205337.16279-1-sashal@kernel.org> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584564820; bh=CP9TqCmkgrHCPPusIn95TMjjPdjHEBSKfNkWw9xBLok=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=AXVsWULsKPZZYQO6x4M94xtQcmtkWWZWc3KRAarY9MwtyJFHbA7un2oWNSr9Aj0Aq 8hjVEfpX+kH4z3lzrm16FQYH+mxtnNz62ddPqawrUW03jswmhntGgILRycLjerWujc s1F0+vUFyeaUEe283dcwLHFlEBN6ni76b9OcC7eE= In-Reply-To: <20200318205337.16279-1-sashal-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="utf-8" To: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Cc: =?UTF-8?q?Michal=20Koutn=C3=BD?= , Suren Baghdasaryan , Tejun Heo , Sasha Levin , cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org From: Michal Koutný [ Upstream commit 9c974c77246460fa6a92c18554c3311c8c83c160 ] 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 Fixes: c03cd7738a83 ("cgroup: Include dying leaders with live threads in PROCS iterations") Signed-off-by: Michal Koutný Signed-off-by: Tejun Heo Signed-off-by: Sasha Levin --- 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 3ba3e6da13a6f..57577075d2049 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 595c52d59f310..a1236b1b80383 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -4461,12 +4461,16 @@ 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; @@ -4524,10 +4528,14 @@ 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 { @@ -4546,11 +4554,12 @@ 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; } } -- 2.20.1