Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751761AbWHSQQt (ORCPT ); Sat, 19 Aug 2006 12:16:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751762AbWHSQQt (ORCPT ); Sat, 19 Aug 2006 12:16:49 -0400 Received: from filfla-vlan276.msk.corbina.net ([213.234.233.49]:9890 "EHLO screens.ru") by vger.kernel.org with ESMTP id S1751761AbWHSQQs (ORCPT ); Sat, 19 Aug 2006 12:16:48 -0400 Date: Sun, 20 Aug 2006 00:40:47 +0400 From: Oleg Nesterov To: Andrew Morton Cc: Thomas Gleixner , Ingo Molnar , Steven Rostedt , Nick Piggin , Linus Torvalds , linux-kernel@vger.kernel.org Subject: Re: [PATCH 4/4] sched_setscheduler: fix? policy checks Message-ID: <20060819204047.GA11410@oleg> References: <20060819193243.GA8648@oleg> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20060819193243.GA8648@oleg> User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3008 Lines: 101 On 08/19, Oleg Nesterov wrote: > > I am not sure this patch is correct: Surely it is not correct. Another attempt ... [PATCH 4/4] sched_setscheduler: fix? policy checks I am not sure this patch is correct: I can't understand what the current code does, and I don't know what it was supposed to do. The comment says: * can't change policy, except between SCHED_NORMAL * and SCHED_BATCH: The code: if (((policy != SCHED_NORMAL && p->policy != SCHED_BATCH) && (policy != SCHED_BATCH && p->policy != SCHED_NORMAL)) && But this is equivalent to: if ( (is_rt_policy(policy) && has_rt_policy(p)) && which means something different. We can't _decrease_ the current ->rt_priority with such a check (if rlim[RLIMIT_RTPRIO] == 0). Probably, it was supposed to be: if ( !(policy == SCHED_NORMAL && p->policy == SCHED_BATCH) && !(policy == SCHED_BATCH && p->policy == SCHED_NORMAL) this matches the comment, but strange: it doesn't allow to _drop_ the realtime priority when rlim[RLIMIT_RTPRIO] == 0. I think the right check would be: /* can't set/change rt policy */ if (is_rt_policy(policy) && policy != p->policy && !rlim_rtprio) return -EPERM; Signed-off-by: Oleg Nesterov --- 2.6.18-rc4/kernel/sched.c~4_policy 2006-08-19 22:03:26.000000000 +0400 +++ 2.6.18-rc4/kernel/sched.c 2006-08-20 00:37:05.000000000 +0400 @@ -4079,27 +4079,25 @@ recheck: * Allow unprivileged RT tasks to decrease priority: */ if (!capable(CAP_SYS_NICE)) { - unsigned long rlim_rtprio; - unsigned long flags; + if (is_rt_policy(policy)) { + unsigned long rlim_rtprio; + unsigned long flags; - if (!lock_task_sighand(p, &flags)) - return -ESRCH; - rlim_rtprio = p->signal->rlim[RLIMIT_RTPRIO].rlim_cur; - unlock_task_sighand(p, &flags); + if (!lock_task_sighand(p, &flags)) + return -ESRCH; + rlim_rtprio = p->signal->rlim[RLIMIT_RTPRIO].rlim_cur; + unlock_task_sighand(p, &flags); + + /* can't set/change the rt policy */ + if (policy != p->policy && !rlim_rtprio) + return -EPERM; + + /* can't increase priority */ + if (param->sched_priority > p->rt_priority && + param->sched_priority > rlim_rtprio) + return -EPERM; + } - /* - * can't change policy, except between SCHED_NORMAL - * and SCHED_BATCH: - */ - if (((policy != SCHED_NORMAL && p->policy != SCHED_BATCH) && - (policy != SCHED_BATCH && p->policy != SCHED_NORMAL)) && - !rlim_rtprio) - return -EPERM; - /* can't increase priority */ - if (is_rt_policy(policy) && - param->sched_priority > p->rt_priority && - param->sched_priority > rlim_rtprio) - return -EPERM; /* can't change other user's priorities */ if ((current->euid != p->euid) && (current->euid != p->uid)) - 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/