/* * This function is exported but must not be called by anything other * than get_page(). It implements the slow path of get_page(). */ bool __get_page_tail(struct page *page) { /* * This takes care of get_page() if run on a tail page * returned by one of the get_user_pages/follow_page variants. * get_user_pages/follow_page itself doesn't need the compound * lock because it runs __get_page_tail_foll() under the * proper PT lock that already serializes against * split_huge_page(). */ unsigned long flags; bool got; struct page *page_head = compound_trans_head(page); /* Ref to put_compound_page() comment. */ if (!__compound_tail_refcounted(page_head)) { smp_rmb(); if (likely(PageTail(page))) { /* * This is a hugetlbfs page or a slab * page. __split_huge_page_refcount * cannot race here. */ VM_BUG_ON(!PageHead(page_head)); __get_page_tail_foll(page, true); return true; } else { /* * __split_huge_page_refcount run * before us, "page" was a THP * tail. The split page_head has been * freed and reallocated as slab or * hugetlbfs page of smaller order * (only possible if reallocated as * slab on x86). */ return false; } } got = false; if (likely(page != page_head && get_page_unless_zero(page_head))) { /* * page_head wasn't a dangling pointer but it * may not be a head page anymore by the time * we obtain the lock. That is ok as long as it * can't be freed from under us. */ flags = compound_lock_irqsave(page_head); /* here __split_huge_page_refcount won't run anymore */ if (likely(PageTail(page))) { __get_page_tail_foll(page, false); got = true; } compound_unlock_irqrestore(page_head, flags); if (unlikely(!got)) put_page(page_head); } return got; }
/* * This function is exported but must not be called by anything other * than get_page(). It implements the slow path of get_page(). */ bool __get_page_tail(struct page *page) { /* * This takes care of get_page() if run on a tail page * returned by one of the get_user_pages/follow_page variants. * get_user_pages/follow_page itself doesn't need the compound * lock because it runs __get_page_tail_foll() under the * proper PT lock that already serializes against * split_huge_page(). */ bool got = false; struct page *page_head; /* * If this is a hugetlbfs page it cannot be split under us. Simply * increment refcount for the head page. */ if (PageHuge(page)) { page_head = compound_head(page); atomic_inc(&page_head->_count); got = true; } else { unsigned long flags; page_head = compound_trans_head(page); if (likely(page != page_head && get_page_unless_zero(page_head))) { /* Ref to put_compound_page() comment. */ if (PageSlab(page_head)) { if (likely(PageTail(page))) { __get_page_tail_foll(page, false); return true; } else { put_page(page_head); return false; } } /* * page_head wasn't a dangling pointer but it * may not be a head page anymore by the time * we obtain the lock. That is ok as long as it * can't be freed from under us. */ flags = compound_lock_irqsave(page_head); /* here __split_huge_page_refcount won't run anymore */ if (likely(PageTail(page))) { __get_page_tail_foll(page, false); got = true; } compound_unlock_irqrestore(page_head, flags); if (unlikely(!got)) put_page(page_head); } } return got; }
/* * This function is exported but must not be called by anything other * than get_page(). It implements the slow path of get_page(). */ bool __get_page_tail(struct page *page) { /* * This takes care of get_page() if run on a tail page * returned by one of the get_user_pages/follow_page variants. * get_user_pages/follow_page itself doesn't need the compound * lock because it runs __get_page_tail_foll() under the * proper PT lock that already serializes against * split_huge_page(). */ unsigned long flags; bool got = false; struct page *page_head = compound_trans_head(page); if (likely(page != page_head && get_page_unless_zero(page_head))) { /* * page_head wasn't a dangling pointer but it * may not be a head page anymore by the time * we obtain the lock. That is ok as long as it * can't be freed from under us. */ flags = compound_lock_irqsave(page_head); /* here __split_huge_page_refcount won't run anymore */ if (likely(PageTail(page))) { __get_page_tail_foll(page, false); got = true; } compound_unlock_irqrestore(page_head, flags); if (unlikely(!got)) put_page(page_head); } return got; }