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Fri, 13 Aug 2021 04:41:36 +0000 Received: from HQMAIL107.nvidia.com (172.20.187.13) by HQMAIL109.nvidia.com (172.20.187.15) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Thu, 12 Aug 2021 21:41:35 -0700 Received: from sandstorm.attlocal.net (172.20.187.5) by mail.nvidia.com (172.20.187.13) with Microsoft SMTP Server id 15.0.1497.2 via Frontend Transport; Fri, 13 Aug 2021 04:41:35 +0000 From: John Hubbard To: Andrew Morton CC: Matthew Wilcox , Christoph Hellwig , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , LKML , , , , John Hubbard Subject: [PATCH v3 3/3] mm/gup: Remove try_get_page(), call try_get_compound_head() directly Date: Thu, 12 Aug 2021 21:41:33 -0700 Message-ID: <20210813044133.1536842-4-jhubbard@nvidia.com> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20210813044133.1536842-1-jhubbard@nvidia.com> References: <20210813044133.1536842-1-jhubbard@nvidia.com> MIME-Version: 1.0 X-NVConfidentiality: public X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 76314af1-ad14-4db4-0d81-08d95e14a265 X-MS-TrafficTypeDiagnostic: BN9PR12MB5099: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:6430; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 13 Aug 2021 04:41:36.3875 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 76314af1-ad14-4db4-0d81-08d95e14a265 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.112.32];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: BN8NAM11FT016.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN9PR12MB5099 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org 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. Cc: Matthew Wilcox Reviewed-by: Christoph Hellwig Signed-off-by: John Hubbard --- 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(-) diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c index 212632d57db9..a834e4672f72 100644 --- a/arch/s390/mm/fault.c +++ b/arch/s390/mm/fault.c @@ -822,7 +822,7 @@ void do_secure_storage_access(struct pt_regs *regs) 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); diff --git a/fs/pipe.c b/fs/pipe.c index 8e6ef62aeb1c..4394b80dc84f 100644 --- a/fs/pipe.c +++ b/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); diff --git a/include/linux/mm.h b/include/linux/mm.h index ba985eaf3f19..f5ab4fd6d48c 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1207,15 +1207,7 @@ bool __must_check try_grab_page(struct page *page, unsigned int flags); 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); /** * folio_put - Decrement the reference count on a folio. diff --git a/mm/gup.c b/mm/gup.c index 886d6148d3d0..7a406d79bd2e 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -62,11 +62,24 @@ static void put_page_refs(struct page *page, int refs) 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);