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 <linux/rcupdate.h> #include <linux/once.h> #include <linux/fs.h> +#include <linux/mm.h> #include <linux/sockptr.h> #include <uapi/linux/net.h> @@ -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")