Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753580Ab2BPPNr (ORCPT ); Thu, 16 Feb 2012 10:13:47 -0500 Received: from mail-ey0-f174.google.com ([209.85.215.174]:41655 "EHLO mail-ey0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751627Ab2BPPNp (ORCPT ); Thu, 16 Feb 2012 10:13:45 -0500 Date: Thu, 16 Feb 2012 19:13:40 +0400 From: Cyrill Gorcunov To: Oleg Nesterov Cc: Vasiliy Kulikov , Andrew Morton , "Eric W. Biederman" , Pavel Emelyanov , Andrey Vagin , KOSAKI Motohiro , Ingo Molnar , "H. Peter Anvin" , Thomas Gleixner , Glauber Costa , Andi Kleen , Tejun Heo , Matt Helsley , Pekka Enberg , Eric Dumazet , Alexey Dobriyan , Valdis.Kletnieks@vt.edu, Michal Marek , Frederic Weisbecker , linux-kernel@vger.kernel.org Subject: Re: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree Message-ID: <20120216151340.GI1905@moon> References: <20120215162222.GA18266@redhat.com> <20120215175319.GG4533@moon> <20120215184336.GA24182@redhat.com> <20120215195610.GJ4533@moon> <20120215195733.GA8021@albatros> <20120215200533.GQ1894@moon> <20120215202538.GK4533@moon> <20120215210934.GL4533@moon> <20120215215807.GM4533@moon> <20120216144954.GA11953@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120216144954.GA11953@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1682 Lines: 58 On Thu, Feb 16, 2012 at 03:49:54PM +0100, Oleg Nesterov wrote: > On 02/16, Cyrill Gorcunov wrote: > > > > +static int access_trylock(struct task_struct *task) > > +{ > > + if (!mutex_trylock(&task->signal->cred_guard_mutex)) > > + return -EBUSY; > > + > > + if (!ptrace_may_access(task, PTRACE_MODE_READ)) { > > + mutex_unlock(&task->signal->cred_guard_mutex); > > + return -EPERM; > > + } > > + > > + return 0; > > +} > > OK, this looks correct, but I don't really understand _trylock. > This means the caller should always retry if -EBUSY, and > kcmp(pid, pid) can never succeed. Sure, kcmp() doesn't make > a lot of sense if pid1 == pid2, but this looks a bit strange. > Hi Oleg, sure I can make it this way, also I think if pid1 == pid2 and idx1 == idx2 I can return 0 immediately. > You could simply do > int mutex_double_lock_killable(struct mutex *m1, struct mutex *m2) > { > int err; > > if (m2 > m1) > swap(m1, m2); > > err = mutex_lock_killable(m1); > > if (!err && likely(m1 != m2)) { > err = mutex_lock_killable_nested(m2); > if (err) > mutex_unlock(m1); > } > > return err; > } > > but I won't insist. Initially I wanted kcmp would be brining minimum impact and if mutex is already taken by someone, we would not sleep but return immediately with -EBUSY and it would be up to caller to deside if to try again or make some delay first. I simply not sure what is better here. Cyrill -- 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/