On Sun, Apr 07, 2019 at 10:05:14AM -0700, Paul E. McKenney wrote: > On Sun, Apr 07, 2019 at 03:46:13PM +0000, Joel Fernandes wrote: > > On Sun, Apr 07, 2019 at 06:59:37AM -0700, Paul E. McKenney 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. > > > > Actually the vmlinux.lds.h file is unused for module building. For ex, if you > > delete include/asm-generic/vmlinux.lds.h , then you can still build > > rcutorture.ko. Did I miss something obvious? In that case the vmlinux.lds.h > > are not needed since the __section annotations automatically place the srcu > > structs in a separate section. > > Hard to argue given that I just deleted include/asm-generic/vmlinux.lds.h, > touched kernel/rcu/rcutorture.c, and rebuilt the corresponding .ko > without errors. ;-) > > Hmmm... Is there some way to place a section into a read-only page, > for example, tagged onto the text section for that module? That would > get rid of a class of bugs, if nothing else. Strictly speaking, the array of pointers in the new srcu section are fixed up at runtime because the srcu_struct(s) they point to can be loaded at a dynamic location in memory. The srcu_struct(s) are themselves in the .bss section of the module and their locations depend on where the .bss section of the module is loaded in memory at load time. I agree that after such relocation fixups are done, there is no reason to keep the array-of-pointers section readable but unfortunately I couldn't figure a way out to make them read-only post the relocations. I copied Jessica Yu who maintains module loading for any input. Jessica, as a summary, we are trying to create a custom ELF section of srcu_struct pointers in kernels modules, and then make the module loader do SRCU initialization from structs pointed to by this section. The srcu_struct themselves are defined on the .bss section. Is there any way we can make this pointer array section read-only *after* the relocation fixups of the array are completed? > > Let me know if you would like me to send a patch separately, or if the > > appended patch for the same in my previous email suffices. > > Please do resend as a formal patch with the above in the commit log. > I doubt that I am the only one needing a bit of module-build education! > And thank you for providing that education, by the way! Sounds great, I will go ahead and send out a patch in the morning for this part. > > > And may I have your Tested-by? > > > > Absolutely, please do and thanks! > > Done, and thank you for giving it a go! You're very welcome. thanks, - Joel _______________________________________________ amd-gfx mailing list amd-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/amd-gfx
