FS-Cache fixes

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Merge tag 'fscache-fixes-20181130' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

Pull fscache and cachefiles fixes from David Howells:
 "Misc fixes:

   - Fix an assertion failure at fs/cachefiles/xattr.c:138 caused by a
     race between a cache object lookup failing and someone attempting
     to reenable that object, thereby triggering an update of the
     object's attributes.

   - Fix an assertion failure at fs/fscache/operation.c:449 caused by a
     split atomic subtract and atomic read that allows a race to happen.

   - Fix a leak of backing pages when simultaneously reading the same
     page from the same object from two or more threads.

   - Fix a hang due to a race between a cache object being discarded and
     the corresponding cookie being reenabled.

  There are also some minor cleanups:

   - Cast an enum value to a different enum type to prevent clang from
     generating a warning. This shouldn't cause any sort of change in
     the emitted code.

   - Use ktime_get_real_seconds() instead of get_seconds(). This is just
     used to uniquify a filename for an object to be placed in the
     graveyard. Objects placed there are deleted by cachfilesd in
     userspace immediately thereafter.

   - Remove an initialised, but otherwise unused variable. This should
     have been entirely optimised away anyway"

* tag 'fscache-fixes-20181130' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs:
  fscache, cachefiles: remove redundant variable 'cache'
  cachefiles: avoid deprecated get_seconds()
  cachefiles: Explicitly cast enumerated type in put_object
  fscache: fix race between enablement and dropping of object
  cachefiles: Fix page leak in cachefiles_read_backing_file while vmscan is active
  fscache: Fix race in fscache_op_complete() due to split atomic_sub & read
  cachefiles: Fix an assertion failure when trying to update a failed object

fs/cachefiles/namei.c

@@ -244,11 +244,13 @@ wait_for_old_object:
 
 	ASSERT(!test_bit(CACHEFILES_OBJECT_ACTIVE, &xobject->flags));
 
-	cache->cache.ops->put_object(&xobject->fscache, cachefiles_obj_put_wait_retry);
+	cache->cache.ops->put_object(&xobject->fscache,
+		(enum fscache_obj_ref_trace)cachefiles_obj_put_wait_retry);
 	goto try_again;
 
 requeue:
-	cache->cache.ops->put_object(&xobject->fscache, cachefiles_obj_put_wait_timeo);
+	cache->cache.ops->put_object(&xobject->fscache,
+		(enum fscache_obj_ref_trace)cachefiles_obj_put_wait_timeo);
 	_leave(" = -ETIMEDOUT");
 	return -ETIMEDOUT;
 }
@@ -336,7 +338,7 @@ static int cachefiles_bury_object(struct cachefiles_cache *cache,
 try_again:
 	/* first step is to make up a grave dentry in the graveyard */
 	sprintf(nbuffer, "%08x%08x",
-		(uint32_t) get_seconds(),
+		(uint32_t) ktime_get_real_seconds(),
 		(uint32_t) atomic_inc_return(&cache->gravecounter));
 
 	/* do the multiway lock magic */

fs/cachefiles/rdwr.c

@@ -535,7 +535,10 @@ static int cachefiles_read_backing_file(struct cachefiles_object *object,
 					    netpage->index, cachefiles_gfp);
 		if (ret < 0) {
 			if (ret == -EEXIST) {
+				put_page(backpage);
+				backpage = NULL;
 				put_page(netpage);
+				netpage = NULL;
 				fscache_retrieval_complete(op, 1);
 				continue;
 			}
@@ -608,7 +611,10 @@ static int cachefiles_read_backing_file(struct cachefiles_object *object,
 					    netpage->index, cachefiles_gfp);
 		if (ret < 0) {
 			if (ret == -EEXIST) {
+				put_page(backpage);
+				backpage = NULL;
 				put_page(netpage);
+				netpage = NULL;
 				fscache_retrieval_complete(op, 1);
 				continue;
 			}
@@ -962,11 +968,8 @@ void cachefiles_uncache_page(struct fscache_object *_object, struct page *page)
 	__releases(&object->fscache.cookie->lock)
 {
 	struct cachefiles_object *object;
-	struct cachefiles_cache *cache;
 
 	object = container_of(_object, struct cachefiles_object, fscache);
-	cache = container_of(object->fscache.cache,
-			     struct cachefiles_cache, cache);
 
 	_enter("%p,{%lu}", object, page->index);
 

fs/cachefiles/xattr.c

@@ -135,7 +135,8 @@ int cachefiles_update_object_xattr(struct cachefiles_object *object,
 	struct dentry *dentry = object->dentry;
 	int ret;
 
-	ASSERT(dentry);
+	if (!dentry)
+		return -ESTALE;
 
 	_enter("%p,#%d", object, auxdata->len);
 

fs/fscache/object.c

@@ -730,6 +730,9 @@ static const struct fscache_state *fscache_drop_object(struct fscache_object *ob
 
 	if (awaken)
 		wake_up_bit(&cookie->flags, FSCACHE_COOKIE_INVALIDATING);
+	if (test_and_clear_bit(FSCACHE_COOKIE_LOOKING_UP, &cookie->flags))
+		wake_up_bit(&cookie->flags, FSCACHE_COOKIE_LOOKING_UP);
+
 
 	/* Prevent a race with our last child, which has to signal EV_CLEARED
 	 * before dropping our spinlock.

include/linux/fscache-cache.h

@@ -196,8 +196,7 @@ static inline void fscache_enqueue_retrieval(struct fscache_retrieval *op)
 static inline void fscache_retrieval_complete(struct fscache_retrieval *op,
 					      int n_pages)
 {
-	atomic_sub(n_pages, &op->n_pages);
+	if (atomic_sub_return_relaxed(n_pages, &op->n_pages) <= 0)
-	if (atomic_read(&op->n_pages) <= 0)
 		fscache_op_complete(&op->op, false);
 }