1 files changed, 77 insertions, 2 deletions

diff --git a/fs/fscache/page.c b/fs/fscache/page.c
index 022a5da8e130..fc76798bd968 100644
--- a/fs/fscache/page.c
+++ b/fs/fscache/page.c
@@ -43,6 +43,75 @@ void __fscache_wait_on_page_write(struct fscache_cookie *cookie, struct page *pa
 EXPORT_SYMBOL(__fscache_wait_on_page_write);
 
 /*
+ * decide whether a page can be released, possibly by cancelling a store to it
+ * - we're allowed to sleep if __GFP_WAIT is flagged
+ */
+bool __fscache_maybe_release_page(struct fscache_cookie *cookie,
+                                  struct page *page,
+                                  gfp_t gfp)
+{
+        struct page *xpage;
+        void *val;
+
+        _enter("%p,%p,%x", cookie, page, gfp);
+
+        rcu_read_lock();
+        val = radix_tree_lookup(&cookie->stores, page->index);
+        if (!val) {
+                rcu_read_unlock();
+                fscache_stat(&fscache_n_store_vmscan_not_storing);
+                __fscache_uncache_page(cookie, page);
+                return true;
+        }
+
+        /* see if the page is actually undergoing storage - if so we can't get
+         * rid of it till the cache has finished with it */
+        if (radix_tree_tag_get(&cookie->stores, page->index,
+                               FSCACHE_COOKIE_STORING_TAG)) {
+                rcu_read_unlock();
+                goto page_busy;
+        }
+
+        /* the page is pending storage, so we attempt to cancel the store and
+         * discard the store request so that the page can be reclaimed */
+        spin_lock(&cookie->stores_lock);
+        rcu_read_unlock();
+
+        if (radix_tree_tag_get(&cookie->stores, page->index,
+                               FSCACHE_COOKIE_STORING_TAG)) {
+                /* the page started to undergo storage whilst we were looking,
+                 * so now we can only wait or return */
+                spin_unlock(&cookie->stores_lock);
+                goto page_busy;
+        }
+
+        xpage = radix_tree_delete(&cookie->stores, page->index);
+        spin_unlock(&cookie->stores_lock);
+
+        if (xpage) {
+                fscache_stat(&fscache_n_store_vmscan_cancelled);
+                fscache_stat(&fscache_n_store_radix_deletes);
+                ASSERTCMP(xpage, ==, page);
+        } else {
+                fscache_stat(&fscache_n_store_vmscan_gone);
+        }
+
+        wake_up_bit(&cookie->flags, 0);
+        if (xpage)
+                page_cache_release(xpage);
+        __fscache_uncache_page(cookie, page);
+        return true;
+
+page_busy:
+        /* we might want to wait here, but that could deadlock the allocator as
+         * the slow-work threads writing to the cache may all end up sleeping
+         * on memory allocation */
+        fscache_stat(&fscache_n_store_vmscan_busy);
+        return false;
+}
+EXPORT_SYMBOL(__fscache_maybe_release_page);
+
+/*
  * note that a page has finished being written to the cache
  */
 static void fscache_end_page_write(struct fscache_object *object,
@@ -57,6 +126,8 @@ static void fscache_end_page_write(struct fscache_object *object,
                 /* delete the page from the tree if it is now no longer
                  * pending */
                 spin_lock(&cookie->stores_lock);
+                radix_tree_tag_clear(&cookie->stores, page->index,
+                                     FSCACHE_COOKIE_STORING_TAG);
                 if (!radix_tree_tag_get(&cookie->stores, page->index,
                                         FSCACHE_COOKIE_PENDING_TAG)) {
                         fscache_stat(&fscache_n_store_radix_deletes);
@@ -640,8 +711,12 @@ static void fscache_write_op(struct fscache_operation *_op)
                 goto superseded;
         }
 
-        radix_tree_tag_clear(&cookie->stores, page->index,
-                             FSCACHE_COOKIE_PENDING_TAG);
+        if (page) {
+                radix_tree_tag_set(&cookie->stores, page->index,
+                                   FSCACHE_COOKIE_STORING_TAG);
+                radix_tree_tag_clear(&cookie->stores, page->index,
+                                     FSCACHE_COOKIE_PENDING_TAG);
+        }
 
         spin_unlock(&cookie->stores_lock);
         spin_unlock(&object->lock);