From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 77B8FC07E85 for ; Sun, 9 Dec 2018 07:21:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2CB6320831 for ; Sun, 9 Dec 2018 07:21:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="SIey4V7D" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2CB6320831 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726125AbeLIHVo (ORCPT ); Sun, 9 Dec 2018 02:21:44 -0500 Received: from mail-pg1-f193.google.com ([209.85.215.193]:44593 "EHLO mail-pg1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726076AbeLIHVn (ORCPT ); Sun, 9 Dec 2018 02:21:43 -0500 Received: by mail-pg1-f193.google.com with SMTP id t13so3524660pgr.11; Sat, 08 Dec 2018 23:21:43 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id; bh=ONkZ9i+vSVBwiKv0jCSx2lBpiXozUtvPXgShMmZkvZE=; b=SIey4V7DZEVEzGD8JerF+CaPVC26cyP/HPBc7f7nqRUzKE6UI7S7QLnQkggx19NmQa Ig7ZsORmTeXQc3bfEe1OThH4VWlJw0vQ94nEiA6DZLp50xjlj3u/0czyJtbl3/uMqukx 3hwCVo2qmVgMBjj+d5eCL4Nu/8O5oAYZApQF6LkwRG8R1u9TPSavHDCxIjUzsVfA4+Dq +xRIaGBYnMj+iiYH4e53BkXlRYkCNJn8J+bxIJS8SN/nRXwuNcgJlh7ISwF5H0+iFE5S oEpr3gQ0FX7l8UBra266bu1JJ/v/WdrQeNbJoU/2OjWhue43XwVg6b1qAa/yspR5MUQu phYg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id; bh=ONkZ9i+vSVBwiKv0jCSx2lBpiXozUtvPXgShMmZkvZE=; b=YhcbDeo2OiRKmeg3cuD78wCoOLihJqpsEV9Vb69mbnWa0UbBYJNMSHCkadtbXMksDB ZpXjkj4YW4AHC2keCqad5puMi4Xknfzig+6hWsJT2+2hCJ1/FwlKvWlK1bQy5SrNolmk kslFd3+guCK6DRnMXrqhEwKW3sXpLFBbgvO9pqR/Y+9FUbABXy9LaxVKhS7vCOUpy8S/ ZVIgsIHMteBQEInsQ03FGo8Ig2rknFYvztBkUDE0TBav/k5ZXfvf2KA6XE3IGUeXFYLD 0bkDVGnA4paZwcl2XcGBqq8KoZEGny/RS34/R/qCn8tN8FTW9hljBBM/bYpiYPRVwP/N k+6A== X-Gm-Message-State: AA+aEWbNKJJYv3JSqvfv1KEjWP9k7b0yWbl/UYSZr/jtirUIq4pPZRQo M8z5Wsmh22g4WrQ39iI5igc= X-Google-Smtp-Source: AFSGD/UeG1S+spJZwpsO7uTIMmtFllcxMzQuBh73tHi/xSlPgrOaMhWIO6j9HLnMvUp8Z8Atp1DtXQ== X-Received: by 2002:a63:ae01:: with SMTP id q1mr6948431pgf.402.1544340102774; Sat, 08 Dec 2018 23:21:42 -0800 (PST) Received: from VM_15_152_centos.localdomain ([193.112.178.48]) by smtp.gmail.com with ESMTPSA id v9sm11425173pfg.144.2018.12.08.23.21.40 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 08 Dec 2018 23:21:42 -0800 (PST) From: gchen.guomin@gmail.com To: "Michael S. Tsirkin" Cc: guominchen , , , Jason Wang , Subject: [PATCH] Fix mm->owner point to a task that does not exists Date: Sun, 9 Dec 2018 15:21:17 +0800 Message-Id: <1544340077-11491-1-git-send-email-gchen.guomin@gmail.com> X-Mailer: git-send-email 1.8.3.1 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: guominchen Under normal circumstances,When do_exit exits, mm->owner will be updated, but when the kernel process calls unuse_mm and exits, mm->owner cannot be updated. And will point to a task that has been released. Below is my issue on vhost_net: A, B are two kernel processes(such as vhost_worker), C is a user space process(such as qemu), and all three use the mm of the user process C. Now, because user process C exits abnormally, the owner of this mm becomes A. When A calls unuse_mm and exits, this mm->ower still points to the A that has been released. When B accesses this mm->owner again, A has been released. Process A Process B vhost_worker() vhost_worker() --------- --------- use_mm() use_mm() ... unuse_mm() tsk->mm=NULL do_exit() page fault exit_mm() access mm->owner can't update owner kernel Oops unuse_mm() Cc: Cc: Cc: "Michael S. Tsirkin" Cc: Jason Wang Cc: Signed-off-by: guominchen --- mm/mmu_context.c | 1 - 1 file changed, 1 deletion(-) diff --git a/mm/mmu_context.c b/mm/mmu_context.c index 3e612ae..185bb23 100644 --- a/mm/mmu_context.c +++ b/mm/mmu_context.c @@ -56,7 +56,6 @@ void unuse_mm(struct mm_struct *mm) task_lock(tsk); sync_mm_rss(mm); - tsk->mm = NULL; /* active_mm is still 'mm' */ enter_lazy_tlb(mm, tsk); task_unlock(tsk); -- 1.8.3.1