FS-Cache: Make cookie relinquishment wait for outstanding reads

Make fscache_relinquish_cookie() log a warning and wait if there are any
outstanding reads left on the cookie it was given.

Signed-off-by: David Howells <dhowells@redhat.com>

3 files changed, 23 insertions, 6 deletions

diff --git a/fs/fscache/cookie.c b/fs/fscache/cookie.c
index 0666996adf80..66be9eccede0 100644
--- a/fs/fscache/cookie.c
+++ b/fs/fscache/cookie.c
@@ -442,22 +442,32 @@ void __fscache_relinquish_cookie(struct fscache_cookie *cookie, int retire)
 
         event = retire ? FSCACHE_OBJECT_EV_RETIRE : FSCACHE_OBJECT_EV_RELEASE;
 
+try_again:
         spin_lock(&cookie->lock);
 
         /* break links with all the active objects */
         while (!hlist_empty(&cookie->backing_objects)) {
+                int n_reads;
                 object = hlist_entry(cookie->backing_objects.first,
                                      struct fscache_object,
                                      cookie_link);
 
                 _debug("RELEASE OBJ%x", object->debug_id);
 
-                if (atomic_read(&object->n_reads)) {
+                set_bit(FSCACHE_COOKIE_WAITING_ON_READS, &cookie->flags);
+                n_reads = atomic_read(&object->n_reads);
+                if (n_reads) {
+                        int n_ops = object->n_ops;
+                        int n_in_progress = object->n_in_progress;
                         spin_unlock(&cookie->lock);
                         printk(KERN_ERR "FS-Cache:"
-                               " Cookie '%s' still has %d outstanding reads\n",
-                               cookie->def->name, atomic_read(&object->n_reads));
-                        BUG();
+                               " Cookie '%s' still has %d outstanding reads (%d,%d)\n",
+                               cookie->def->name,
+                               n_reads, n_ops, n_in_progress);
+                        wait_on_bit(&cookie->flags, FSCACHE_COOKIE_WAITING_ON_READS,
+                                    fscache_wait_bit, TASK_UNINTERRUPTIBLE);
+                        printk("Wait finished\n");
+                        goto try_again;
                 }
 
                 /* detach each cache object from the object cookie */
diff --git a/fs/fscache/operation.c b/fs/fscache/operation.c
index 30afdfa7aec7..c857ab824d6e 100644
--- a/fs/fscache/operation.c
+++ b/fs/fscache/operation.c
@@ -340,8 +340,14 @@ void fscache_put_operation(struct fscache_operation *op)
 
         object = op->object;
 
-        if (test_bit(FSCACHE_OP_DEC_READ_CNT, &op->flags))
-                atomic_dec(&object->n_reads);
+        if (test_bit(FSCACHE_OP_DEC_READ_CNT, &op->flags)) {
+                if (atomic_dec_and_test(&object->n_reads)) {
+                        clear_bit(FSCACHE_COOKIE_WAITING_ON_READS,
+                                  &object->cookie->flags);
+                        wake_up_bit(&object->cookie->flags,
+                                    FSCACHE_COOKIE_WAITING_ON_READS);
+                }
+        }
 
         /* now... we may get called with the object spinlock held, so we
          * complete the cleanup here only if we can immediately acquire the
diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h
index 9879183b55d8..e3d6d939d959 100644
--- a/include/linux/fscache-cache.h
+++ b/include/linux/fscache-cache.h
@@ -301,6 +301,7 @@ struct fscache_cookie {
 #define FSCACHE_COOKIE_PENDING_FILL     3       /* T if pending initial fill on object */
 #define FSCACHE_COOKIE_FILLING          4       /* T if filling object incrementally */
 #define FSCACHE_COOKIE_UNAVAILABLE      5       /* T if cookie is unavailable (error, etc) */
+#define FSCACHE_COOKIE_WAITING_ON_READS 6       /* T if cookie is waiting on reads */
 };
 
 extern struct fscache_cookie fscache_fsdef_index;