Subject: Re: linux-next link failure

From: Mel Gorman <[email-masked]>
Date: Tue, 24 Jul 2012 11:18:41 +0100

On Mon, Jul 23, 2012 at 02:16:49PM -0400, Mark Salter wrote:
> Today's linux-next has a link failure on no-mmu systems:
> 
>   fs/built-in.o: In function `nfs_file_direct_read':
>   (.text+0x80968): undefined reference to `get_kernel_page'
>   fs/built-in.o: In function `nfs_file_direct_write':
>   (.text+0x81178): undefined reference to `get_kernel_page'
> 
> The problem is that get_kernel_page does not exist if CONFIG_MMU is not
> defined. This is the patch that added get_kernel_page():
> 
>   mm: add get_kernel_page[s] for pinning of kernel addresses for I/O
> 
> and the reference to get_kernelpage was added with:
> 
>   nfs: enable swap on NFS
> 

Thanks, the inline patch should fix it.

Adding Andrew to cc. Andrew, merging this is tricky but the basic intent is
to move get_kernel_pages from memory.c to swap.c which affects these patches

mm: add get_kernel_page[s] for pinning of kernel addresses for I/O
mm: add support for a filesystem to activate swap files and use direct_IO for writing swap pages
mm: swap: implement generic handler for swap_activate
mm: add support for direct_IO to highmem pages

The build fix is needed for the first patch but the inlined version will
collide as the later patches affect the same code. I'm attaching an
alternative version that can be applied directly to the first patch.
This will cause a collision in "mm: add support for direct_IO
to highmem pages" but all that is needed is to rename the hunk affecting
memory.c to swap.c .

---8<---
buildfix: mm: add get_kernel_page[s] for pinning of kernel addresses for I/O

get_kernel_pages was put in memory.c beside get_user_pages but this only
works for CONFIG_MMU. As there is nothing special to be done for
!CONFIG_MMU, this build fix moves the functions to mm/swap.c which is
the next best fit.

Signed-off-by: Mel Gorman <[email-masked]>

diff --git a/mm/memory.c b/mm/memory.c
index 8a989f1..caaef7f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1852,58 +1852,6 @@ next_page:
 EXPORT_SYMBOL(__get_user_pages);
 
 /*
- * get_kernel_pages() - pin kernel pages in memory
- * @kiov:	An array of struct kvec structures
- * @nr_segs:	number of segments to pin
- * @write:	pinning for read/write, currently ignored
- * @pages:	array that receives pointers to the pages pinned.
- *		Should be at least nr_segs long.
- *
- * Returns number of pages pinned. This may be fewer than the number
- * requested. If nr_pages is 0 or negative, returns 0. If no pages
- * were pinned, returns -errno. Each page returned must be released
- * with a put_page() call when it is finished with.
- */
-int get_kernel_pages(const struct kvec *kiov, int nr_segs, int write,
-		struct page **pages)
-{
-	int seg;
-
-	for (seg = 0; seg < nr_segs; seg++) {
-		if (WARN_ON(kiov[seg].iov_len != PAGE_SIZE))
-			return seg;
-
-		pages[seg] = kmap_to_page(kiov[seg].iov_base);
-		page_cache_get(pages[seg]);
-	}
-
-	return seg;
-}
-EXPORT_SYMBOL_GPL(get_kernel_pages);
-
-/*
- * get_kernel_page() - pin a kernel page in memory
- * @start:	starting kernel address
- * @write:	pinning for read/write, currently ignored
- * @pages:	array that receives pointer to the page pinned.
- *		Must be at least nr_segs long.
- *
- * Returns 1 if page is pinned. If the page was not pinned, returns
- * -errno. The page returned must be released with a put_page() call
- * when it is finished with.
- */
-int get_kernel_page(unsigned long start, int write, struct page **pages)
-{
-	const struct kvec kiov = {
-		.iov_base = (void *)start,
-		.iov_len = PAGE_SIZE
-	};
-
-	return get_kernel_pages(&kiov, 1, write, pages);
-}
-EXPORT_SYMBOL_GPL(get_kernel_page);
-
-/*
  * fixup_user_fault() - manually resolve a user page fault
  * @tsk:	the task_struct to use for page fault accounting, or
  *		NULL if faults are not to be recorded.
diff --git a/mm/swap.c b/mm/swap.c
index 4e7e2ec..7782588 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -236,6 +236,58 @@ void put_pages_list(struct list_head *pages)
 }
 EXPORT_SYMBOL(put_pages_list);
 
+/*
+ * get_kernel_pages() - pin kernel pages in memory
+ * @kiov:	An array of struct kvec structures
+ * @nr_segs:	number of segments to pin
+ * @write:	pinning for read/write, currently ignored
+ * @pages:	array that receives pointers to the pages pinned.
+ *		Should be at least nr_segs long.
+ *
+ * Returns number of pages pinned. This may be fewer than the number
+ * requested. If nr_pages is 0 or negative, returns 0. If no pages
+ * were pinned, returns -errno. Each page returned must be released
+ * with a put_page() call when it is finished with.
+ */
+int get_kernel_pages(const struct kvec *kiov, int nr_segs, int write,
+		struct page **pages)
+{
+	int seg;
+
+	for (seg = 0; seg < nr_segs; seg++) {
+		if (WARN_ON(kiov[seg].iov_len != PAGE_SIZE))
+			return seg;
+
+		pages[seg] = kmap_to_page(kiov[seg].iov_base);
+		page_cache_get(pages[seg]);
+	}
+
+	return seg;
+}
+EXPORT_SYMBOL_GPL(get_kernel_pages);
+
+/*
+ * get_kernel_page() - pin a kernel page in memory
+ * @start:	starting kernel address
+ * @write:	pinning for read/write, currently ignored
+ * @pages:	array that receives pointer to the page pinned.
+ *		Must be at least nr_segs long.
+ *
+ * Returns 1 if page is pinned. If the page was not pinned, returns
+ * -errno. The page returned must be released with a put_page() call
+ * when it is finished with.
+ */
+int get_kernel_page(unsigned long start, int write, struct page **pages)
+{
+	const struct kvec kiov = {
+		.iov_base = (void *)start,
+		.iov_len = PAGE_SIZE
+	};
+
+	return get_kernel_pages(&kiov, 1, write, pages);
+}
+EXPORT_SYMBOL_GPL(get_kernel_page);
+
 static void pagevec_lru_move_fn(struct pagevec *pvec,
 	void (*move_fn)(struct page *page, struct lruvec *lruvec, void *arg),
 	void *arg)
>>From e38c5c6dad49d87b97ae589b2b7ac477ae7615b0 Mon Sep 17 00:00:00 2001
From: Mel Gorman <[email-masked]>
Date: Tue, 24 Jul 2012 11:13:26 +0100
Subject: [PATCH] buildfix: mm: add get_kernel_page[s] for pinning of kernel
 addresses for I/O

get_kernel_pages was put in memory.c beside get_user_pages but this only
works for CONFIG_MMU. As there is nothing special to be done for
!CONFIG_MMU, this build fix moves the functions to mm/swap.c which is
the next best fit.

Signed-off-by: Mel Gorman <[email-masked]>

diff --git a/mm/memory.c b/mm/memory.c
index 8a989f1..caaef7f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1852,58 +1852,6 @@ next_page:
 EXPORT_SYMBOL(__get_user_pages);

 /*
- * get_kernel_pages() - pin kernel pages in memory
- * @kiov:	An array of struct kvec structures
- * @nr_segs:	number of segments to pin
- * @write:	pinning for read/write, currently ignored
- * @pages:	array that receives pointers to the pages pinned.
- *		Should be at least nr_segs long.
- *
- * Returns number of pages pinned. This may be fewer than the number
- * requested. If nr_pages is 0 or negative, returns 0. If no pages
- * were pinned, returns -errno. Each page returned must be released
- * with a put_page() call when it is finished with.
- */
-int get_kernel_pages(const struct kvec *kiov, int nr_segs, int write,
-		struct page **pages)
-{
-	int seg;
-
-	for (seg = 0; seg < nr_segs; seg++) {
-		if (WARN_ON(kiov[seg].iov_len != PAGE_SIZE))
-			return seg;
-
-		pages[seg] = kmap_to_page(kiov[seg].iov_base);
-		page_cache_get(pages[seg]);
-	}
-
-	return seg;
-}
-EXPORT_SYMBOL_GPL(get_kernel_pages);
-
-/*
- * get_kernel_page() - pin a kernel page in memory
- * @start:	starting kernel address
- * @write:	pinning for read/write, currently ignored
- * @pages:	array that receives pointer to the page pinned.
- *		Must be at least nr_segs long.
- *
- * Returns 1 if page is pinned. If the page was not pinned, returns
- * -errno. The page returned must be released with a put_page() call
- * when it is finished with.
- */
-int get_kernel_page(unsigned long start, int write, struct page **pages)
-{
-	const struct kvec kiov = {
-		.iov_base = (void *)start,
-		.iov_len = PAGE_SIZE
-	};
-
-	return get_kernel_pages(&kiov, 1, write, pages);
-}
-EXPORT_SYMBOL_GPL(get_kernel_page);
-
-/*
  * fixup_user_fault() - manually resolve a user page fault
  * @tsk:	the task_struct to use for page fault accounting, or
  *		NULL if faults are not to be recorded.
diff --git a/mm/swap.c b/mm/swap.c
index 4e7e2ec..7782588 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -236,6 +236,58 @@ void put_pages_list(struct list_head *pages)
 }
 EXPORT_SYMBOL(put_pages_list);

+/*
+ * get_kernel_pages() - pin kernel pages in memory
+ * @kiov:	An array of struct kvec structures
+ * @nr_segs:	number of segments to pin
+ * @write:	pinning for read/write, currently ignored
+ * @pages:	array that receives pointers to the pages pinned.
+ *		Should be at least nr_segs long.
+ *
+ * Returns number of pages pinned. This may be fewer than the number
+ * requested. If nr_pages is 0 or negative, returns 0. If no pages
+ * were pinned, returns -errno. Each page returned must be released
+ * with a put_page() call when it is finished with.
+ */
+int get_kernel_pages(const struct kvec *kiov, int nr_segs, int write,
+		struct page **pages)
+{
+	int seg;
+
+	for (seg = 0; seg < nr_segs; seg++) {
+		if (WARN_ON(kiov[seg].iov_len != PAGE_SIZE))
+			return seg;
+
+		pages[seg] = kmap_to_page(kiov[seg].iov_base);
+		page_cache_get(pages[seg]);
+	}
+
+	return seg;
+}
+EXPORT_SYMBOL_GPL(get_kernel_pages);
+
+/*
+ * get_kernel_page() - pin a kernel page in memory
+ * @start:	starting kernel address
+ * @write:	pinning for read/write, currently ignored
+ * @pages:	array that receives pointer to the page pinned.
+ *		Must be at least nr_segs long.
+ *
+ * Returns 1 if page is pinned. If the page was not pinned, returns
+ * -errno. The page returned must be released with a put_page() call
+ * when it is finished with.
+ */
+int get_kernel_page(unsigned long start, int write, struct page **pages)
+{
+	const struct kvec kiov = {
+		.iov_base = (void *)start,
+		.iov_len = PAGE_SIZE
+	};
+
+	return get_kernel_pages(&kiov, 1, write, pages);
+}
+EXPORT_SYMBOL_GPL(get_kernel_page);
+
 static void pagevec_lru_move_fn(struct pagevec *pvec,
 	void (*move_fn)(struct page *page, struct lruvec *lruvec, void *arg),
 	void *arg)
---
 mm/memory.c |   53 -----------------------------------------------------
 mm/swap.c   |   52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 52 insertions(+), 53 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index bd41f00..caaef7f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1852,59 +1852,6 @@ next_page:
 EXPORT_SYMBOL(__get_user_pages);
 
 /*
- * get_kernel_pages() - pin kernel pages in memory
- * @kiov:	An array of struct kvec structures
- * @nr_segs:	number of segments to pin
- * @write:	pinning for read/write, currently ignored
- * @pages:	array that receives pointers to the pages pinned.
- *		Should be at least nr_segs long.
- *
- * Returns number of pages pinned. This may be fewer than the number
- * requested. If nr_pages is 0 or negative, returns 0. If no pages
- * were pinned, returns -errno. Each page returned must be released
- * with a put_page() call when it is finished with.
- */
-int get_kernel_pages(const struct kvec *kiov, int nr_segs, int write,
-		struct page **pages)
-{
-	int seg;
-
-	for (seg = 0; seg < nr_segs; seg++) {
-		if (WARN_ON(kiov[seg].iov_len != PAGE_SIZE))
-			return seg;
-
-		/* virt_to_page sanity checks the PFN */
-		pages[seg] = virt_to_page(kiov[seg].iov_base);
-		page_cache_get(pages[seg]);
-	}
-
-	return seg;
-}
-EXPORT_SYMBOL_GPL(get_kernel_pages);
-
-/*
- * get_kernel_page() - pin a kernel page in memory
- * @start:	starting kernel address
- * @write:	pinning for read/write, currently ignored
- * @pages:	array that receives pointer to the page pinned.
- *		Must be at least nr_segs long.
- *
- * Returns 1 if page is pinned. If the page was not pinned, returns
- * -errno. The page returned must be released with a put_page() call
- * when it is finished with.
- */
-int get_kernel_page(unsigned long start, int write, struct page **pages)
-{
-	const struct kvec kiov = {
-		.iov_base = (void *)start,
-		.iov_len = PAGE_SIZE
-	};
-
-	return get_kernel_pages(&kiov, 1, write, pages);
-}
-EXPORT_SYMBOL_GPL(get_kernel_page);
-
-/*
  * fixup_user_fault() - manually resolve a user page fault
  * @tsk:	the task_struct to use for page fault accounting, or
  *		NULL if faults are not to be recorded.
diff --git a/mm/swap.c b/mm/swap.c
index 4e7e2ec..ff83e96 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -236,6 +236,58 @@ void put_pages_list(struct list_head *pages)
 }
 EXPORT_SYMBOL(put_pages_list);
 
+/*
+ * get_kernel_pages() - pin kernel pages in memory
+ * @kiov:	An array of struct kvec structures
+ * @nr_segs:	number of segments to pin
+ * @write:	pinning for read/write, currently ignored
+ * @pages:	array that receives pointers to the pages pinned.
+ *		Should be at least nr_segs long.
+ *
+ * Returns number of pages pinned. This may be fewer than the number
+ * requested. If nr_pages is 0 or negative, returns 0. If no pages
+ * were pinned, returns -errno. Each page returned must be released
+ * with a put_page() call when it is finished with.
+ */
+int get_kernel_pages(const struct kvec *kiov, int nr_segs, int write,
+		struct page **pages)
+{
+	int seg;
+
+	for (seg = 0; seg < nr_segs; seg++) {
+		if (WARN_ON(kiov[seg].iov_len != PAGE_SIZE))
+			return seg;
+
+		/* virt_to_page sanity checks the PFN */
+		pages[seg] = virt_to_page(kiov[seg].iov_base);
+		page_cache_get(pages[seg]);
+	}
+
+	return seg;
+}
+EXPORT_SYMBOL_GPL(get_kernel_pages);
+
+/*
+ * get_kernel_page() - pin a kernel page in memory
+ * @start:	starting kernel address
+ * @write:	pinning for read/write, currently ignored
+ * @pages:	array that receives pointer to the page pinned.
+ *		Must be at least nr_segs long.
+ *
+ * Returns 1 if page is pinned. If the page was not pinned, returns
+ * -errno. The page returned must be released with a put_page() call
+ * when it is finished with.
+ */
+int get_kernel_page(unsigned long start, int write, struct page **pages)
+{
+	const struct kvec kiov = {
+		.iov_base = (void *)start,
+		.iov_len = PAGE_SIZE
+	};
+
+	return get_kernel_pages(&kiov, 1, write, pages);
+}
+
 static void pagevec_lru_move_fn(struct pagevec *pvec,
 	void (*move_fn)(struct page *page, struct lruvec *lruvec, void *arg),
 	void *arg)