From: John Hubbard <jhubbard@xxxxxxxxxx> Subject: mm/gup: remove try_get_page(), call try_get_compound_head() directly try_get_page() is very similar to try_get_compound_head(), and in fact try_get_page() has fallen a little behind in terms of maintenance: try_get_compound_head() handles speculative page references more thoroughly. There are only two try_get_page() callsites, so just call try_get_compound_head() directly from those, and remove try_get_page() entirely. Also, seeing as how this changes try_get_compound_head() into a non-static function, provide some kerneldoc documentation for it. Link: https://lkml.kernel.org/r/20210813044133.1536842-4-jhubbard@xxxxxxxxxx Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx> Reviewed-by: Christoph Hellwig <hch@xxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx> Cc: Heiko Carstens <hca@xxxxxxxxxxxxx> Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- arch/s390/mm/fault.c | 2 +- fs/pipe.c | 2 +- include/linux/mm.h | 10 +--------- mm/gup.c | 21 +++++++++++++++++---- 4 files changed, 20 insertions(+), 15 deletions(-) --- a/arch/s390/mm/fault.c~mm-gup-remove-try_get_page-call-try_get_compound_head-directly +++ a/arch/s390/mm/fault.c @@ -817,7 +817,7 @@ void do_secure_storage_access(struct pt_ break; case KERNEL_FAULT: page = phys_to_page(addr); - if (unlikely(!try_get_page(page))) + if (unlikely(!try_get_compound_head(page, 1))) break; rc = arch_make_page_accessible(page); put_page(page); --- a/fs/pipe.c~mm-gup-remove-try_get_page-call-try_get_compound_head-directly +++ a/fs/pipe.c @@ -191,7 +191,7 @@ EXPORT_SYMBOL(generic_pipe_buf_try_steal */ bool generic_pipe_buf_get(struct pipe_inode_info *pipe, struct pipe_buffer *buf) { - return try_get_page(buf->page); + return try_get_compound_head(buf->page, 1); } EXPORT_SYMBOL(generic_pipe_buf_get); --- a/include/linux/mm.h~mm-gup-remove-try_get_page-call-try_get_compound_head-directly +++ a/include/linux/mm.h @@ -1217,15 +1217,7 @@ bool __must_check try_grab_page(struct p struct page *try_grab_compound_head(struct page *page, int refs, unsigned int flags); - -static inline __must_check bool try_get_page(struct page *page) -{ - page = compound_head(page); - if (WARN_ON_ONCE(page_ref_count(page) <= 0)) - return false; - page_ref_inc(page); - return true; -} +struct page *try_get_compound_head(struct page *page, int refs); static inline void put_page(struct page *page) { --- a/mm/gup.c~mm-gup-remove-try_get_page-call-try_get_compound_head-directly +++ a/mm/gup.c @@ -62,11 +62,24 @@ static void put_page_refs(struct page *p put_page(page); } -/* - * Return the compound head page with ref appropriately incremented, - * or NULL if that failed. +/** + * try_get_compound_head() - return the compound head page with refcount + * appropriately incremented, or NULL if that failed. + * + * This handles potential refcount overflow correctly. It also works correclty + * for various lockless get_user_pages()-related callers, due to the use of + * page_cache_add_speculative(). + * + * Even though the name includes "compound_head", this function is still + * appropriate for callers that have a non-compound @page to get. + * + * @page: pointer to page to be gotten + * @refs: the value to add to the page's refcount + * + * Return: head page (with refcount appropriately incremented) for success, or + * NULL upon failure. */ -static inline struct page *try_get_compound_head(struct page *page, int refs) +struct page *try_get_compound_head(struct page *page, int refs) { struct page *head = compound_head(page); _
