Messages in this thread | | | Subject | Re: [PATCH 2/4] powerpc: Prepare to support kernel handling of IOMMU map/unmap | From | Benjamin Herrenschmidt <> | Date | Sun, 16 Jun 2013 14:26:58 +1000 |
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> +#if defined(CONFIG_SPARSEMEM_VMEMMAP) || defined(CONFIG_FLATMEM) > +int realmode_get_page(struct page *page) > +{ > + if (PageCompound(page)) > + return -EAGAIN; > + > + get_page(page); > + > + return 0; > +} > +EXPORT_SYMBOL_GPL(realmode_get_page); > + > +int realmode_put_page(struct page *page) > +{ > + if (PageCompound(page)) > + return -EAGAIN; > + > + if (!atomic_add_unless(&page->_count, -1, 1)) > + return -EAGAIN; > + > + return 0; > +} > +EXPORT_SYMBOL_GPL(realmode_put_page); > +#endif
Several worries here, mostly that if the generic code ever changes (something gets added to get_page() that makes it no-longer safe for use in real mode for example, or some other condition gets added to put_page()), we go out of sync and potentially end up with very hard and very subtle bugs.
It might be worth making sure that:
- This is reviewed by some generic VM people (and make sure they understand why we need to do that)
- A comment is added to get_page() and put_page() to make sure that if they are changed in any way, dbl check the impact on our realmode_get_page() (or "ping" us to make sure things are still ok).
Cheers, Ben.
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