From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joel Fernandes Subject: Re: [PATCH RFC tip/core/rcu 0/4] Forbid static SRCU use in modules Date: Tue, 2 Apr 2019 14:40:54 -0400 Message-ID: <20190402184054.GA18150@google.com> References: <20190402142816.GA13084@linux.ibm.com> <886051277.1395.1554218080591.JavaMail.zimbra@efficios.com> <20190402152334.GC4102@linux.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20190402152334.GC4102-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-nvdimm-bounces-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org Sender: "Linux-nvdimm" To: "Paul E. McKenney" Cc: David Howells , amd-gfx-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org, Thomas Gleixner , linux-nvdimm-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org, Peter Zijlstra , fweisbec , dri-devel-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org, Lai Jiangshan , linux-kernel , rostedt , Josh Triplett , rcu-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Eric Dumazet , Mathieu Desnoyers , Oleg Nesterov , dipankar , Andrew Morton , Ingo Molnar List-Id: dri-devel@lists.freedesktop.org On Tue, Apr 02, 2019 at 08:23:34AM -0700, Paul E. McKenney wrote: > On Tue, Apr 02, 2019 at 11:14:40AM -0400, Mathieu Desnoyers wrote: > > ----- On Apr 2, 2019, at 10:28 AM, paulmck paulmck-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org wrote: > > > > > Hello! > > > > > > This series prohibits use of DEFINE_SRCU() and DEFINE_STATIC_SRCU() > > > by loadable modules. The reason for this prohibition is the fact > > > that using these two macros within modules requires that the size of > > > the reserved region be increased, which is not something we want to > > > be doing all that often. Instead, loadable modules should define an > > > srcu_struct and invoke init_srcu_struct() from their module_init function > > > and cleanup_srcu_struct() from their module_exit function. Note that > > > modules using call_srcu() will also need to invoke srcu_barrier() from > > > their module_exit function. > > > > This arbitrary API limitation seems weird. > > > > Isn't there a way to allow modules to use DEFINE_SRCU and DEFINE_STATIC_SRCU > > while implementing them with dynamic allocation under the hood ? > > Although call_srcu() already has initialization hooks, some would > also be required in srcu_read_lock(), and I am concerned about adding > memory allocation at that point, especially given the possibility > of memory-allocation failure. And the possibility that the first > srcu_read_lock() happens in an interrupt handler or similar. > > Or am I missing a trick here? Hi Paul, Which 'reserved region' are you referring to? Isn't this region also used for non-module cases in which case the same problem applies to non-modules? thanks! - Joel