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SubjectRe: [PATCH RFC tip/core/rcu 0/4] Forbid static SRCU use in modules
----- On Apr 7, 2019, at 9:59 AM, paulmck paulmck@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 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 ?

Thanks,

Mathieu

--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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