[PATCH 11/22] CacheFiles: Permit the page lock state to be monitored

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Add a function to install a monitor on the page lock waitqueue for a particular
page, thus allowing the page being unlocked to be detected.

This is used by CacheFiles to detect read completion on a page in the backing
filesystem so that it can then copy the data to the waiting netfs page.

Signed-Off-By: David Howells <[email protected]>

 include/linux/pagemap.h |    5 +++++
 mm/filemap.c            |   19 +++++++++++++++++++
 2 files changed, 24 insertions(+), 0 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index d1049b6..452fdcf 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -220,6 +220,11 @@ static inline void wait_on_page_fscache_write(struct page *page)
 extern void end_page_fscache_write(struct page *page);
+ * Add an arbitrary waiter to a page's wait queue
+ */
+extern void add_page_wait_queue(struct page *page, wait_queue_t *waiter);
  * Fault a userspace page into pagetables.  Return non-zero on a fault.
  * This assumes that two userspace pages are always sufficient.  That's
diff --git a/mm/filemap.c b/mm/filemap.c
index 21aeee9..e48e862 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -518,6 +518,25 @@ void fastcall wait_on_page_bit(struct page *page, int bit_nr)
+ * add_page_wait_queue - Add an arbitrary waiter to a page's wait queue
+ * @page - Page defining the wait queue of interest
+ * @waiter - Waiter to add to the queue
+ *
+ * Add an arbitrary @waiter to the wait queue for the nominated @page.
+ */
+void add_page_wait_queue(struct page *page, wait_queue_t *waiter)
+	wait_queue_head_t *q = page_waitqueue(page);
+	unsigned long flags;
+	spin_lock_irqsave(&q->lock, flags);
+	__add_wait_queue(q, waiter);
+	spin_unlock_irqrestore(&q->lock, flags);
  * unlock_page - unlock a locked page
  * @page: the page

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