Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S270499AbTHQTMD (ORCPT ); Sun, 17 Aug 2003 15:12:03 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S270501AbTHQTMD (ORCPT ); Sun, 17 Aug 2003 15:12:03 -0400 Received: from fmr02.intel.com ([192.55.52.25]:24023 "EHLO caduceus.fm.intel.com") by vger.kernel.org with ESMTP id S270499AbTHQTMA (ORCPT ); Sun, 17 Aug 2003 15:12:00 -0400 Message-ID: <3F3FD2E7.9030808@intel.com> Date: Sun, 17 Aug 2003 22:09:27 +0300 From: Vladimir Kondratiev User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.4) Gecko/20030624 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Linux Kernel Mailing List , Marcelo Tosatti Subject: [PATCH] Re: Kernel threads resource leakage X-Enigmail-Version: 0.76.2.0 X-Enigmail-Supports: pgp-inline, pgp-mime Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2229 Lines: 56 I do not subscribed to the list, thus please in your reply CC me (vladimir.kondratiev@intel.com) Some time ago, I reported problem WRT resource leakage in kernel_thread. (2.4.20) To demonstrate it, I submitted program that uses /proc file to display some info and to start/stop kernel thread. I don't want to re-post this code again. Finally, I found that resource leak present only if you create kernel_thread as non-root. With my previous example, do "insmod" as root, while perform actual thread creation/destruction (echo "+" >/proc/kthread etc.) as non-root. To demonstrate it better, I added to /proc 'read' procedure content of "struct user_struct" (current->user). It makes clear, that in this case current->user->processes do not decremented when thread destroyed, and eventually reaches user limit (usually 4k processes). At this point, this user can do nothing. Problem leaves in "reparent_to_init" code in kernel/sched.c; there current->user is simply changed to point to INIT_USER without proper resource management. Does it worth inclusion in 2.4.22? Following patch fixes this bug. I verified that with this patch applied, kernel_thread behaves properly. --- kernel/sched.c.orig 2003-08-17 20:12:14.000000000 +0300 +++ kernel/sched.c 2003-08-17 21:21:08.000000000 +0300 @@ -1274,8 +1274,16 @@ this_task->cap_permitted = CAP_FULL_SET; this_task->keep_capabilities = 0; memcpy(this_task->rlim, init_task.rlim, sizeof(*(this_task->rlim))); - this_task->user = INIT_USER; - + if (this_task->uid) { /* not root? switch user */ + struct user_struct *old_user = this_task->user, + *new_user = INIT_USER; + this_task->uid = 0; + this_task->user = new_user; + atomic_inc(&new_user->__count); + atomic_inc(&new_user->processes); + atomic_dec(&old_user->processes); + free_uid(old_user); + } spin_unlock(&runqueue_lock); write_unlock_irq(&tasklist_lock); } - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/