FS-Cache: Fix handling of an attempt to store a page that is now beyond EOF

Fix the handling of an attempt to store a page that is now beyond EOF.  This
may happen, for example, if the page got pushed for storage before the netfs
file got truncated on the server.  In such a case, we should just remove the
excessive pages from the cookie->stores radix tree and wake up the waiter.

This can be seen in /proc/fs/fscache/stats on this line:

	Stores : ops=350 run=1895 pgs=1545 rxd=1727 olm=9

where olm=N has N > 0.

Reported-by: Milosz Tanski <milosz@adfin.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Milosz Tanski <milosz@adfin.com>

diff --git a/fs/fscache/page.c b/fs/fscache/page.c
index 7f5c658af755f9b43296c1dacfab5def788c4a1c..b4730cf52aec9172727816820174fb53d7e001b8 100644 (file)
--- a/fs/fscache/page.c
+++ b/fs/fscache/page.c
@@ -755,6 +755,7 @@ static void fscache_write_op(struct fscache_operation *_op)
        struct fscache_object *object = op->op.object;
        struct fscache_cookie *cookie;
        struct page *page;
+       pgoff_t index;
        unsigned n;
        void *results[1];
        int ret;
@@ -803,7 +804,7 @@ static void fscache_write_op(struct fscache_operation *_op)
        _debug("gang %d [%lx]", n, page->index);
        if (page->index > op->store_limit) {
                fscache_stat(&fscache_n_store_pages_over_limit);
-               goto superseded;
+               goto page_beyond_limit;
        }
 
        radix_tree_tag_set(&cookie->stores, page->index,
@@ -829,6 +830,40 @@ static void fscache_write_op(struct fscache_operation *_op)
        _leave("");
        return;
 
+page_beyond_limit:
+       spin_unlock(&object->lock);
+
+page_beyond_limit_unlocked:
+       /* pages that are now beyond the end of the storage object must have
+        * their pending storage records cleared.
+        */
+       index = page->index;
+       radix_tree_tag_clear(&cookie->stores, page->index,
+                            FSCACHE_COOKIE_PENDING_TAG);
+       if (!radix_tree_tag_get(&cookie->stores, page->index,
+                               FSCACHE_COOKIE_STORING_TAG)) {
+               fscache_stat(&fscache_n_store_radix_deletes);
+               radix_tree_delete(&cookie->stores, page->index);
+               page_cache_release(page);
+       }
+       if (!need_resched()) {
+               n = radix_tree_gang_lookup_tag(&cookie->stores, results,
+                                              index + 1, 1,
+                                              FSCACHE_COOKIE_PENDING_TAG);
+               if (n == 1) {
+                       page = results[0];
+                       goto page_beyond_limit_unlocked;
+               }
+               spin_unlock(&cookie->stores_lock);
+               wake_up_bit(&cookie->flags, 0);
+       } else {
+               spin_unlock(&cookie->stores_lock);
+       }
+
+       fscache_enqueue_operation(&op->op);
+       _leave("");
+       return;
+
 superseded:
        /* this writer is going away and there aren't any more things to
         * write */