From patchwork Fri Jan 24 11:40:15 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Michal_Koutn=C3=BD?= X-Patchwork-Id: 11350105 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id D6D8C139A for ; Fri, 24 Jan 2020 11:40:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BF5C324125 for ; Fri, 24 Jan 2020 11:40:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2392058AbgAXLkd (ORCPT ); Fri, 24 Jan 2020 06:40:33 -0500 Received: from mx2.suse.de ([195.135.220.15]:50776 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2391200AbgAXLkd (ORCPT ); Fri, 24 Jan 2020 06:40:33 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 43407B149; Fri, 24 Jan 2020 11:40:30 +0000 (UTC) From: =?utf-8?q?Michal_Koutn=C3=BD?= To: cgroups@vger.kernel.org Cc: alex.shi@linux.alibaba.com, guro@fb.com, hannes@cmpxchg.org, kernel-team@android.com, linger.lee@mediatek.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mediatek@lists.infradead.org, lizefan@huawei.com, matthias.bgg@gmail.com, shuah@kernel.org, surenb@google.com, tj@kernel.org, tomcherry@google.com Subject: [PATCH v2 1/3] cgroup: Iterate tasks that did not finish do_exit() Date: Fri, 24 Jan 2020 12:40:15 +0100 Message-Id: <20200124114017.8363-2-mkoutny@suse.com> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20200124114017.8363-1-mkoutny@suse.com> References: <20200120145635.GA30904@blackbody.suse.cz> <20200124114017.8363-1-mkoutny@suse.com> MIME-Version: 1.0 Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org 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 Tested-by: Suren Baghdasaryan --- 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; } }