From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeremy Fitzhardinge Subject: Re: [BUG][PATCH -mm] avoid BUG() in __stop_machine_run() Date: Thu, 19 Jun 2008 08:51:06 -0700 Message-ID: <485A806A.2090602@goop.org> References: <20080611225945.4da7bb7f.akpm@linux-foundation.org> <485A03E6.2090509@hitachi.com> <200806192012.44459.rusty@rustcorp.com.au> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <200806192012.44459.rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org> Sender: kernel-testers-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Rusty Russell Cc: Hidehiro Kawai , Andrew Morton , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, kernel-testers-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, sugita , Satoshi OSHIMA , Ingo Molnar Rusty Russell wrote: > On Thursday 19 June 2008 16:59:50 Hidehiro Kawai wrote: > >> When a process loads a kernel module, __stop_machine_run() is called, and >> it calls sched_setscheduler() to give newly created kernel threads highest >> priority. However, the process can have no CAP_SYS_NICE which required >> for sched_setscheduler() to increase the priority. For example, SystemTap >> loads its module with only CAP_SYS_MODULE. In this case, >> sched_setscheduler() returns -EPERM, then BUG() is called. >> > > Hi Hidehiro, > > Nice catch. This can happen in the current code, it just doesn't > BUG(). > > >> Failure of sched_setscheduler() wouldn't be a real problem, so this >> patch just ignores it. >> > > Well, it can mean that the stop_machine blocks indefinitely. Better > than a BUG(), but we should aim higher. > > >> Or, should we give the CAP_SYS_NICE capability temporarily? >> > > I don't think so. It can be seen from another thread, and in theory > that should not see something random. Worse, they can change it from > another thread. > > How's this? > > sched_setscheduler: add a flag to control access checks > > Hidehiro Kawai noticed that sched_setscheduler() can fail in > stop_machine: it calls sched_setscheduler() from insmod, which can > have CAP_SYS_MODULE without CAP_SYS_NICE. > > This simply introduces a flag to allow us to disable the capability > checks for internal callers (this is simpler than splitting the > sched_setscheduler() function, since it loops checking permissions). > What about? int sched_setscheduler(struct task_struct *p, int policy, struct sched_param *param) { return __sched_setscheduler(p, policy, param, true); } int sched_setscheduler_nocheck(struct task_struct *p, int policy, struct sched_param *param) { return __sched_setscheduler(p, policy, param, false); } (With the appropriate transformation of sched_setscheduler -> __) Better than scattering stray true/falses around the code. J -- To unsubscribe from this list: send the line "unsubscribe kernel-testers" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html