This is a fun little race. Dramatis personae: Pages P0, P1 are consecutive and aligned. Threads A, B, C. Page P0 is allocated to the page cache. Page P1 is free. Thread A calls find_get_entry() P0 is returned from xas_load() Thread B removes the page from the page cache (eg truncate, invalidatepage). P0 is buddy-merged with P1. Thread C calls alloc_pages, order 1, does not specify GFP_COMP. P0 now has refcount 1. Thread A calls page_cache_get_speculative(). P0 has refcount 2. Thread C calls __free_page(P0, 1) put_page_testzero is _false_. Do not call free_the_page(). Thread A calls put_page(P0) We free P0 and nobody knows to free P1. Weird solution: In __free_page(), if put_page_testzero() fails and page is not PageHead, convert it to a compound page. Then the put_page() by Thread A will free P1. Better ideas?
