----- On Apr 7, 2019, at 3:32 PM, Joel Fernandes, Google joel(a)joelfernandes.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(a)linux.ibm.com 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
> >> > torture works fine with rcutorture built as a module. Putting further
> >> > in kernel/module.c verified that the kernel is able to find the srcu
> >> > just fine. You could squash the below patch into this one or apply it
> >> > 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 ?