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[73.241.150.58]) by smtp.gmail.com with ESMTPSA id x28sm23667645pfj.73.2020.08.18.01.08.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 18 Aug 2020 01:08:26 -0700 (PDT) Subject: Re: [PATCH v5 1/3] net: introduce helper sendpage_ok() in include/linux/net.h To: Coly Li , linux-block@vger.kernel.org, linux-nvme@lists.infradead.org Cc: netdev@vger.kernel.org, stable@vger.kernel.org, linux-kernel@vger.kernel.org, Chaitanya Kulkarni , Christoph Hellwig , Hannes Reinecke , Jan Kara , Jens Axboe , Mikhail Skorzhinskii , Philipp Reisner , Sagi Grimberg , Vlastimil Babka References: <20200816070814.6806-1-colyli@suse.de> From: Eric Dumazet Message-ID: <66b4f454-dc97-a23e-81d6-0c547dced694@gmail.com> Date: Tue, 18 Aug 2020 01:08:25 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <20200816070814.6806-1-colyli@suse.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 8/16/20 12:08 AM, Coly Li wrote: > The original problem was from nvme-over-tcp code, who mistakenly uses > kernel_sendpage() to send pages allocated by __get_free_pages() without > __GFP_COMP flag. Such pages don't have refcount (page_count is 0) on > tail pages, sending them by kernel_sendpage() may trigger a kernel panic > from a corrupted kernel heap, because these pages are incorrectly freed > in network stack as page_count 0 pages. > > This patch introduces a helper sendpage_ok(), it returns true if the > checking page, > - is not slab page: PageSlab(page) is false. > - has page refcount: page_count(page) is not zero > > All drivers who want to send page to remote end by kernel_sendpage() > may use this helper to check whether the page is OK. If the helper does > not return true, the driver should try other non sendpage method (e.g. > sock_no_sendpage()) to handle the page. > > > > diff --git a/include/linux/net.h b/include/linux/net.h > index d48ff1180879..a807fad31958 100644 > --- a/include/linux/net.h > +++ b/include/linux/net.h > @@ -21,6 +21,7 @@ > #include > #include > #include > +#include > #include > > #include > @@ -286,6 +287,21 @@ do { \ > #define net_get_random_once_wait(buf, nbytes) \ > get_random_once_wait((buf), (nbytes)) > > +/* > + * E.g. XFS meta- & log-data is in slab pages, or bcache meta > + * data pages, or other high order pages allocated by > + * __get_free_pages() without __GFP_COMP, which have a page_count > + * of 0 and/or have PageSlab() set. We cannot use send_page for > + * those, as that does get_page(); put_page(); and would cause > + * either a VM_BUG directly, or __page_cache_release a page that > + * would actually still be referenced by someone, leading to some > + * obscure delayed Oops somewhere else. > + */ > +static inline bool sendpage_ok(struct page *page) > +{ > + return (!PageSlab(page) && page_count(page) >= 1); > +} > return (A); Can simply be written : return A; In this case : return !PageSlab(page) && page_count(page) >= 1; BTW, do you have plans to refine code added with commit a10674bf2406afc2554f9c7d31b2dc65d6a27fd9 ("tcp: detecting the misuse of .sendpage for Slab objects")