From: Jason Gunthorpe <jgg@xxxxxxxxxx> Subject: mm/gup: combine put_compound_head() and unpin_user_page() These functions accomplish the same thing but have different implementations. unpin_user_page() has a bug where it calls mod_node_page_state() after calling put_page() which creates a risk that the page could have been hot-uplugged from the system. Fix this by using put_compound_head() as the only implementation. __unpin_devmap_managed_user_page() and related can be deleted as well in favour of the simpler, but slower, version in put_compound_head() that has an extra atomic page_ref_sub, but always calls put_page() which internally contains the special devmap code. Move put_compound_head() to be directly after try_grab_compound_head() so people can find it in future. Link: https://lkml.kernel.org/r/0-v1-6730d4ee0d32+40e6-gup_combine_put_jgg@xxxxxxxxxx Fixes: 1970dc6f5226 ("mm/gup: /proc/vmstat: pin_user_pages (FOLL_PIN) reporting") Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx> Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx> Reviewed-by: Ira Weiny <ira.weiny@xxxxxxxxx> Reviewed-by: Jan Kara <jack@xxxxxxx> CC: Joao Martins <joao.m.martins@xxxxxxxxxx> CC: Jonathan Corbet <corbet@xxxxxxx> CC: Dan Williams <dan.j.williams@xxxxxxxxx> CC: Dave Chinner <david@xxxxxxxxxxxxx> CC: Christoph Hellwig <hch@xxxxxxxxxxxxx> CC: Jane Chu <jane.chu@xxxxxxxxxx> CC: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> CC: Michal Hocko <mhocko@xxxxxxxx> CC: Mike Kravetz <mike.kravetz@xxxxxxxxxx> CC: Shuah Khan <shuah@xxxxxxxxxx> CC: Muchun Song <songmuchun@xxxxxxxxxxxxx> CC: Vlastimil Babka <vbabka@xxxxxxx> CC: Matthew Wilcox <willy@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/gup.c | 103 +++++++++++------------------------------------------ 1 file changed, 23 insertions(+), 80 deletions(-) --- a/mm/gup.c~mm-up-combine-put_compound_head-and-unpin_user_page +++ a/mm/gup.c @@ -123,6 +123,28 @@ static __maybe_unused struct page *try_g return NULL; } +static void put_compound_head(struct page *page, int refs, unsigned int flags) +{ + if (flags & FOLL_PIN) { + mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED, + refs); + + if (hpage_pincount_available(page)) + hpage_pincount_sub(page, refs); + else + refs *= GUP_PIN_COUNTING_BIAS; + } + + VM_BUG_ON_PAGE(page_ref_count(page) < refs, page); + /* + * Calling put_page() for each ref is unnecessarily slow. Only the last + * ref needs a put_page(). + */ + if (refs > 1) + page_ref_sub(page, refs - 1); + put_page(page); +} + /** * try_grab_page() - elevate a page's refcount by a flag-dependent amount * @@ -177,41 +199,6 @@ bool __must_check try_grab_page(struct p return true; } -#ifdef CONFIG_DEV_PAGEMAP_OPS -static bool __unpin_devmap_managed_user_page(struct page *page) -{ - int count, refs = 1; - - if (!page_is_devmap_managed(page)) - return false; - - if (hpage_pincount_available(page)) - hpage_pincount_sub(page, 1); - else - refs = GUP_PIN_COUNTING_BIAS; - - count = page_ref_sub_return(page, refs); - - mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED, 1); - /* - * devmap page refcounts are 1-based, rather than 0-based: if - * refcount is 1, then the page is free and the refcount is - * stable because nobody holds a reference on the page. - */ - if (count == 1) - free_devmap_managed_page(page); - else if (!count) - __put_page(page); - - return true; -} -#else -static bool __unpin_devmap_managed_user_page(struct page *page) -{ - return false; -} -#endif /* CONFIG_DEV_PAGEMAP_OPS */ - /** * unpin_user_page() - release a dma-pinned page * @page: pointer to page to be released @@ -223,28 +210,7 @@ static bool __unpin_devmap_managed_user_ */ void unpin_user_page(struct page *page) { - int refs = 1; - - page = compound_head(page); - - /* - * For devmap managed pages we need to catch refcount transition from - * GUP_PIN_COUNTING_BIAS to 1, when refcount reach one it means the - * page is free and we need to inform the device driver through - * callback. See include/linux/memremap.h and HMM for details. - */ - if (__unpin_devmap_managed_user_page(page)) - return; - - if (hpage_pincount_available(page)) - hpage_pincount_sub(page, 1); - else - refs = GUP_PIN_COUNTING_BIAS; - - if (page_ref_sub_and_test(page, refs)) - __put_page(page); - - mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED, 1); + put_compound_head(compound_head(page), 1, FOLL_PIN); } EXPORT_SYMBOL(unpin_user_page); @@ -2009,29 +1975,6 @@ EXPORT_SYMBOL(get_user_pages_unlocked); * This code is based heavily on the PowerPC implementation by Nick Piggin. */ #ifdef CONFIG_HAVE_FAST_GUP - -static void put_compound_head(struct page *page, int refs, unsigned int flags) -{ - if (flags & FOLL_PIN) { - mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED, - refs); - - if (hpage_pincount_available(page)) - hpage_pincount_sub(page, refs); - else - refs *= GUP_PIN_COUNTING_BIAS; - } - - VM_BUG_ON_PAGE(page_ref_count(page) < refs, page); - /* - * Calling put_page() for each ref is unnecessarily slow. Only the last - * ref needs a put_page(). - */ - if (refs > 1) - page_ref_sub(page, refs - 1); - put_page(page); -} - #ifdef CONFIG_GUP_GET_PTE_LOW_HIGH /* _
