From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mathieu Desnoyers Subject: Re: [PATCH RFC tip/core/rcu 0/4] Forbid static SRCU use in modules Date: Sun, 7 Apr 2019 16:41:36 -0400 (EDT) Message-ID: <1632568795.549.1554669696728.JavaMail.zimbra@efficios.com> References: <20190402142816.GA13084@linux.ibm.com> <20190403162039.GA14111@linux.ibm.com> <20190405232835.GA24702@linux.ibm.com> <20190406230613.GA187766@google.com> <20190407133941.GC14111@linux.ibm.com> <20190407135937.GA30053@linux.ibm.com> <134026717.535.1554665176677.JavaMail.zimbra@efficios.com> <20190407193202.GA30934@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190407193202.GA30934@localhost> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-nvdimm-bounces-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org Sender: "Linux-nvdimm" To: "Joel Fernandes, Google" Cc: David Howells , amd-gfx , linux-nvdimm , Peter Zijlstra , fweisbec , dri-devel , Lai Jiangshan , linux-kernel , rostedt , Josh Triplett , rcu , Eric Dumazet , Thomas Gleixner , Oleg Nesterov , dipankar , Andrew Morton , paulmck , Ingo Molnar List-Id: dri-devel@lists.freedesktop.org ----- On Apr 7, 2019, at 3:32 PM, Joel Fernandes, Google joel-QYYGw3jwrUn5owFQY34kdNi2O/JbrIOy@public.gmane.org wrote: > On Sun, Apr 07, 2019 at 03:26:16PM -0400, Mathieu Desnoyers wrote: >> ----- On Apr 7, 2019, at 9:59 AM, paulmck paulmck-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org wrote: >> >> > On Sun, Apr 07, 2019 at 06:39:41AM -0700, Paul E. McKenney wrote: >> >> On Sat, Apr 06, 2019 at 07:06:13PM -0400, Joel Fernandes wrote: >> > >> > [ . . . ] >> > >> >> > > diff --git a/include/asm-generic/vmlinux.lds.h >> >> > > b/include/asm-generic/vmlinux.lds.h >> >> > > index f8f6f04c4453..c2d919a1566e 100644 >> >> > > --- a/include/asm-generic/vmlinux.lds.h >> >> > > +++ b/include/asm-generic/vmlinux.lds.h >> >> > > @@ -338,6 +338,10 @@ >> >> > > KEEP(*(__tracepoints_ptrs)) /* Tracepoints: pointer array */ \ >> >> > > __stop___tracepoints_ptrs = .; \ >> >> > > *(__tracepoints_strings)/* Tracepoints: strings */ \ >> >> > > + . = ALIGN(8); \ >> >> > > + __start___srcu_struct = .; \ >> >> > > + *(___srcu_struct_ptrs) \ >> >> > > + __end___srcu_struct = .; \ >> >> > > } \ >> >> > >> >> > This vmlinux linker modification is not needed. I tested without it and srcu >> >> > torture works fine with rcutorture built as a module. Putting further prints >> >> > in kernel/module.c verified that the kernel is able to find the srcu structs >> >> > just fine. You could squash the below patch into this one or apply it on top >> >> > of the dev branch. >> >> >> >> Good point, given that otherwise FORTRAN named common blocks would not >> >> work. >> >> >> >> But isn't one advantage of leaving that stuff in the RO_DATA_SECTION() >> >> macro that it can be mapped read-only? Or am I suffering from excessive >> >> optimism? >> > >> > And to answer the other question, in the case where I am suffering from >> > excessive optimism, it should be a separate commit. Please see below >> > for the updated original commit thus far. >> > >> > And may I have your Tested-by? >> >> Just to confirm: does the cleanup performed in the modules going >> notifier end up acting as a barrier first before freeing the memory ? >> If not, is it explicitly stated that a barrier must be issued before >> module unload ? >> > > You mean rcu_barrier? It is mentioned in the documentation that this is the > responsibility of the module writer to prevent delays for all modules. It's a srcu barrier yes. Considering it would be a barrier specific to the srcu domain within that module, I don't see how it would cause delays for "all" modules if we implicitly issue the barrier on module unload. What am I missing ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com