On Thu, 12 Nov 2015, Jessica Yu wrote: > +++ Josh Poimboeuf [12/11/15 11:05 -0600]: > > On Thu, Nov 12, 2015 at 04:03:45PM +0100, Petr Mladek wrote: > > > On Thu 2015-11-12 14:22:28, Miroslav Benes wrote: > > > > On Thu, 12 Nov 2015, Petr Mladek wrote: > > > > > > >Maybe I am missing something but isn't it necessary to call vfree() > > > on > > > > > > >info somewhere in the end? > > > > > > > > > > > > So free_copy() will call vfree(info->hdr), except in livepatch > > > modules > > > > > > we want to keep all the elf section information stored there, so we > > > > > > avoid calling free_copy(), As for the info struct itself, if you > > > look > > > > > > at the init_module and finit_module syscall definitions in > > > > > > kernel/module.c, you will see that info is actually a local function > > > > > > variable, simply passed in to the call to load_module(), and will be > > > > > > automatically deallocated when the syscall returns. :-) No need to > > > > > > explicitly free info. > > > > > > > > > > We still have to free the copied or preserved structures when > > > > > the module is unloaded. > > > > > > > > ...freeing what we allocated. We need to free info->hdr somewhere if not > > > > here and also mod_arch_specific struct where the patch module is > > > removed. > > > > This would unfortunately lead to changes in arch-specific code in > > > > module.c. For example in arch/s390/kernel/module.c there is vfree call > > > on > > > > part of mod_arch_specific in module_finalize. We would call it only if > > > the > > > > flag mentioned above is not set and at the same time we would need to > > > call > > > > it when the patch module is being removed. > > > > > > Sigh, I am afraid that the flag is not enough. IMHO, we need to split > > > the load finalizing functions into two pieces. One will be always > > > called when the module load is finalized. The other part will free > > > the load_info. It will be called either when the load is finalized or > > > when the module is unloaded, depending on if we want to preserve > > > the load_info. > > > > > > Sigh, it is getting complicated. But let's see how it looks in reality. > > > > At the other end of the spectrum, we could do the simplest thing > > possible: _always_ save the data (even if CONFIG_LIVEPATCH is disabled). > > > > (gdb) print sizeof(*info) > > $3 = 96 > > (gdb) p sizeof(*info->hdr) > > $4 = 64 > > s390 mod_arch_syminfo struct: 24 bytes by my reckoning. > > > > So between info, info->hdr, and s390 mod_arch_syminfo, we're talking > > about 184 bytes on s390 and 160 bytes on x86_64. That seems like > > peanuts compared to the size of a typical module. The benefit is that > > the code would be simpler because we don't have any special cases and > > the structs would automatically get freed with the module struct when > > the module gets unloaded. Agreed. mod_arch_specific contains more things on certain architectures, but compared to the size of a module it is still not much. > > I think I agree with Josh on this one (except, I would always save > load_info if it is a livepatch module, instead of for every module in the > !CONFIG_LIVEPATCH case, and we can just check modinfo to see if it is > a livepatch module). > > If the tradeoff here is between simplicity and readibility of code vs. > saving some extra space (and by the looks of it, not a lot), I think I > would choose having clear code over saving some bytes of memory. Hard > coding checks and edge cases imo might cause confusion and trouble > down the road. I agree this seems like the best approach. So if we preserve mod_arch_syminfo (in case of s390) we should free it not in module_finalize, but somewhere in free_module... where module_arch_cleanup() is called... and also module_arch_freeing_init() is called there too. And what you find there for s390 is vfree(mod->arch.syminfo); mod->arch.syminfo = NULL; Well, it does nothing here, because mod->arch.syminfo is already NULL. It was freed in module_finalize. So we can even remove this code from module_finalize and all should be fine. At least for s390. As for load_info, I don't have a strong opinion whether to keep it for all modules or for livepatch modules only. Miroslav -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
