On Mon 15-08-22 16:26:46, Matthew Wilcox wrote: > On Mon, Aug 15, 2022 at 05:06:18PM +0200, Michal Hocko wrote: > > > + * This function gives proper page_ext of a memory section > > > + * during race with the offline operation on a memory block > > > + * this section falls into. Not using this function to get > > > + * page_ext of a page, in code paths where extra refcount > > > + * is not taken on that page eg: pfn walking, can lead to > > > + * use-after-free access of page_ext. > > > > I do not think this is really useful comment, it goes into way too much > > detail about memory hotplug yet not enough to actually understand the > > interaction because there are no references to the actual > > synchronization scheme. I would go with something like: > > > > /* > > * Get a page_ext associated with the given page. Returns NULL if > > * no such page_ext exists otherwise ensures that the page_ext will > > * stay alive until page_ext_put is called. > > * This implies a non-sleeping context. > > */ > > I'd go further and turn this into kernel-doc: > > /** > * page_ext_get() - Get the extended information for a page. > * @page: The page we're interested in. > * > * Ensures that the page_ext will remain valid until page_ext_put() > * is called. > * > * Return: NULL if no page_ext exists for this page. > * Context: Any context. Caller may not sleep until they have called > * page_ext_put(). > */ Yes, thanks! -- Michal Hocko SUSE Labs
