----- On Apr 7, 2019, at 10:27 PM, paulmck paulmck@xxxxxxxxxxxxx wrote: > On Sun, Apr 07, 2019 at 09:07:18PM +0000, Joel Fernandes wrote: >> On Sun, Apr 07, 2019 at 04:41:36PM -0400, Mathieu Desnoyers wrote: >> > >> > ----- On Apr 7, 2019, at 3:32 PM, Joel Fernandes, Google joel@xxxxxxxxxxxxxxxxx >> > wrote: >> > >> > > On Sun, Apr 07, 2019 at 03:26:16PM -0400, Mathieu Desnoyers wrote: >> > >> ----- On Apr 7, 2019, at 9:59 AM, paulmck paulmck@xxxxxxxxxxxxx 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 ? >> >> Yes you are right. I thought of this after I just sent my email. I think it >> makes sense for srcu case to do and could avoid a class of bugs. > > If there are call_srcu() callbacks outstanding, the module writer still > needs the srcu_barrier() because otherwise callbacks arrive after > the module text has gone, which will be disappoint the CPU when it > tries fetching instructions that are no longer mapped. If there are > no call_srcu() callbacks from that module, then there is no need for > srcu_barrier() either way. > > So if an srcu_barrier() is needed, the module developer needs to > supply it. When you say "callbacks arrive after the module text has gone", I think you assume that free_module() is invoked before the MODULE_STATE_GOING notifiers are called. But it's done in the opposite order: going notifiers are called first, and then free_module() is invoked. So AFAIU it would be safe to issue the srcu_barrier() from the module going notifier. Or am I missing something ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com _______________________________________________ amd-gfx mailing list amd-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/amd-gfx
