From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oleg Nesterov Subject: Re: [PATCH] pid: change task_struct::pid to read-only Date: Tue, 17 Dec 2013 16:40:04 +0100 Message-ID: <20131217154004.GA21656@redhat.com> References: <8aa73d2b884439496f87d5f34c12ba9b4b40f7e5.1377032086.git.rgb@redhat.com> <20131217153611.GA18321@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20131217153611.GA18321@redhat.com> Sender: linux-kernel-owner@vger.kernel.org To: Richard Guy Briggs Cc: linux-audit@redhat.com, linux-kernel@vger.kernel.org, Eric Paris , Peter Zijlstra List-Id: linux-audit@redhat.com On 12/17, Oleg Nesterov wrote: > > On 12/16, Richard Guy Briggs wrote: > > > > task->pid is only ever assigned once (well ok, twice). For system health and > > secure logging confidence, make it const to make it much more intentional when > > it is being changed. > > Hmm. I am a bit suprized you decided to constify task->pid, but OK. > > And we can do the same with task->signal, this can actually help to generate > a better code, probably. > > > if (!thread_group_leader(tsk)) { > > struct task_struct *leader = tsk->group_leader; > > + /* tast_struct::pid is const pid_t, hence the ugly cast */ > > + pid_t *pid_p = (pid_t*)&(tsk->pid); > > > > sig->notify_count = -1; /* for exit_notify() */ > > for (;;) { > > @@ -950,7 +952,7 @@ static int de_thread(struct task_struct *tsk) > > * Note: The old leader also uses this pid until release_task > > * is called. Odd but simple and correct. > > */ > > - tsk->pid = leader->pid; > > + *pid_p = leader->pid; > > Well, imho this (and de_thread) looks a bit ugly. Perhaps we should add > something like > > #define ASSIGN_CONST(l, r) (*(typeof(r) *)&(l) = (r)) > > into compiler.h ? Or even #define ASSIGN_CONST(l, r) \ ({ BUILD_BUG_ON(sizeof(l) != sizeof(r)); *(typeof(r) *)&(l) = (r); }) perhaps it will have more users. Oleg.