From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f69.google.com (mail-wm0-f69.google.com [74.125.82.69]) by kanga.kvack.org (Postfix) with ESMTP id 855AD828E2 for ; Thu, 28 Jul 2016 15:43:03 -0400 (EDT) Received: by mail-wm0-f69.google.com with SMTP id l4so24933479wml.0 for ; Thu, 28 Jul 2016 12:43:03 -0700 (PDT) Received: from mail-wm0-f66.google.com (mail-wm0-f66.google.com. [74.125.82.66]) by mx.google.com with ESMTPS id fs5si14658320wjb.260.2016.07.28.12.42.50 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 28 Jul 2016 12:42:50 -0700 (PDT) Received: by mail-wm0-f66.google.com with SMTP id q128so12643805wma.1 for ; Thu, 28 Jul 2016 12:42:50 -0700 (PDT) From: Michal Hocko Subject: [PATCH 10/10] oom, oom_reaper: allow to reap mm shared by the kthreads Date: Thu, 28 Jul 2016 21:42:34 +0200 Message-Id: <1469734954-31247-11-git-send-email-mhocko@kernel.org> In-Reply-To: <1469734954-31247-1-git-send-email-mhocko@kernel.org> References: <1469734954-31247-1-git-send-email-mhocko@kernel.org> Sender: owner-linux-mm@kvack.org List-ID: To: linux-mm@kvack.org Cc: Andrew Morton , Tetsuo Handa , Oleg Nesterov , David Rientjes , Vladimir Davydov , Michal Hocko From: Michal Hocko oom reaper was skipped for an mm which is shared with the kernel thread (aka use_mm()). The primary concern was that such a kthread might want to read from the userspace memory and see zero page as a result of the oom reaper action. This seems to be overly conservative because none of the current use_mm() users need to do copy_from_user or get_user. aio code used to rely on copy_from_user but this is long gone along with use_mm() usage in fs/aio.c. We currently have only 3 users in the kernel: - ffs_user_copy_worker, ep_user_copy_worker only do copy_to_iter() - vhost_worker needs to copy from userspace but it relies on the safe __get_user_mm, copy_from_user_mm resp. copy_from_iter_mm Add a note to use_mm about the copy_from_user risk and allow the oom killer to invoke the oom_reaper for mms shared with kthreads. This will practically cause all the sane use cases to be reapable. Signed-off-by: Michal Hocko --- mm/mmu_context.c | 6 ++++++ mm/oom_kill.c | 14 +++++++------- 2 files changed, 13 insertions(+), 7 deletions(-) diff --git a/mm/mmu_context.c b/mm/mmu_context.c index f802c2d216a7..61a7a90250be 100644 --- a/mm/mmu_context.c +++ b/mm/mmu_context.c @@ -16,6 +16,12 @@ * mm context. * (Note: this routine is intended to be called only * from a kernel thread context) + * + * Do not use copy_from_user/__get_user from this context + * and use the safe copy_from_user_mm/__get_user_mm because + * the address space might got reclaimed behind the back by + * the oom_reaper so an unexpected zero page might be + * encountered. */ void use_mm(struct mm_struct *mm) { diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 6ccf63fbfc72..ca83b1706e13 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -894,13 +894,7 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p, continue; if (same_thread_group(p, victim)) continue; - if (unlikely(p->flags & PF_KTHREAD) || is_global_init(p)) { - /* - * We cannot use oom_reaper for the mm shared by this - * process because it wouldn't get killed and so the - * memory might be still used. Hide the mm from the oom - * killer to guarantee OOM forward progress. - */ + if (is_global_init(p)) { can_oom_reap = false; set_bit(MMF_OOM_SKIP, &mm->flags); pr_info("oom killer %d (%s) has mm pinned by %d (%s)\n", @@ -908,6 +902,12 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p, task_pid_nr(p), p->comm); continue; } + /* + * No use_mm() user needs to read from the userspace so we are + * ok to reap it. + */ + if (unlikely(p->flags & PF_KTHREAD)) + continue; do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, true); } rcu_read_unlock(); -- 2.8.1 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org