Merge tag 'fscache-20130702' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

Pull FS-Cache updates from David Howells:
 "This contains a number of fixes for various FS-Cache issues plus some
  cleanups.  The commits are, in order:

   1) Provide a system wait_on_atomic_t() and wake_up_atomic_t() sharing
      the bit-wait table (enhancement for #8).

   2) Don't put spin_lock() in a while-condition as spin_lock() may have
      a do {} while(0) wrapper (cleanup).

   3) Symbolically name i_mutex lock classes rather than using numbers
      in CacheFiles (cleanup).

   4) Don't sleep in page release if __GFP_FS is not set (deadlock vs
      ext4).

   5) Uninline fscache_object_init() (cleanup for #7).

   6) Wrap checks on object state (cleanup for #7).

   7) Simplify the object state machine by separating work states from
      wait states.

   8) Simplify cookie retention by objects (NULL pointer deref fix).

   9) Remove unused list_to_page() macro (cleanup).

  10) Make the remaining-pages counter in the retrieval op atomic
      (assertion failure fix).

  11) Don't use spin_is_locked() in assertions (assertion failure fix)"

* tag 'fscache-20130702' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs:
  FS-Cache: Don't use spin_is_locked() in assertions
  FS-Cache: The retrieval remaining-pages counter needs to be atomic_t
  cachefiles: remove unused macro list_to_page()
  FS-Cache: Simplify cookie retention for fscache_objects, fixing oops
  FS-Cache: Fix object state machine to have separate work and wait states
  FS-Cache: Wrap checks on object state
  FS-Cache: Uninline fscache_object_init()
  FS-Cache: Don't sleep in page release if __GFP_FS is not set
  CacheFiles: name i_mutex lock class explicitly
  fs/fscache: remove spin_lock() from the condition in while()
  Add wait_on_atomic_t() and wake_up_atomic_t()

2 files changed, 113 insertions, 86 deletions

diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h
index 5dfa0aa216b6..a9ff9a36b86d 100644
--- a/include/linux/fscache-cache.h
+++ b/include/linux/fscache-cache.h
@@ -97,7 +97,8 @@ struct fscache_operation {
 #define FSCACHE_OP_WAITING      4       /* cleared when op is woken */
 #define FSCACHE_OP_EXCLUSIVE    5       /* exclusive op, other ops must wait */
 #define FSCACHE_OP_DEC_READ_CNT 6       /* decrement object->n_reads on destruction */
-#define FSCACHE_OP_KEEP_FLAGS   0x0070  /* flags to keep when repurposing an op */
+#define FSCACHE_OP_UNUSE_COOKIE 7       /* call fscache_unuse_cookie() on completion */
+#define FSCACHE_OP_KEEP_FLAGS   0x00f0  /* flags to keep when repurposing an op */
 
         enum fscache_operation_state state;
         atomic_t                usage;
@@ -150,7 +151,7 @@ struct fscache_retrieval {
         void                    *context;       /* netfs read context (pinned) */
         struct list_head        to_do;          /* list of things to be done by the backend */
         unsigned long           start_time;     /* time at which retrieval started */
-        unsigned                n_pages;        /* number of pages to be retrieved */
+        atomic_t                n_pages;        /* number of pages to be retrieved */
 };
 
 typedef int (*fscache_page_retrieval_func_t)(struct fscache_retrieval *op,
@@ -194,15 +195,14 @@ static inline void fscache_enqueue_retrieval(struct fscache_retrieval *op)
 static inline void fscache_retrieval_complete(struct fscache_retrieval *op,
                                               int n_pages)
 {
-        op->n_pages -= n_pages;
-        if (op->n_pages <= 0)
+        atomic_sub(n_pages, &op->n_pages);
+        if (atomic_read(&op->n_pages) <= 0)
                 fscache_op_complete(&op->op, true);
 }
 
 /**
  * fscache_put_retrieval - Drop a reference to a retrieval operation
  * @op: The retrieval operation affected
- * @n_pages: The number of pages to account for
  *
  * Drop a reference to a retrieval operation.
  */
@@ -314,6 +314,7 @@ struct fscache_cache_ops {
 struct fscache_cookie {
         atomic_t                        usage;          /* number of users of this cookie */
         atomic_t                        n_children;     /* number of children of this cookie */
+        atomic_t                        n_active;       /* number of active users of netfs ptrs */
         spinlock_t                      lock;
         spinlock_t                      stores_lock;    /* lock on page store tree */
         struct hlist_head               backing_objects; /* object(s) backing this file/index */
@@ -326,13 +327,11 @@ struct fscache_cookie {
 
         unsigned long                   flags;
 #define FSCACHE_COOKIE_LOOKING_UP       0       /* T if non-index cookie being looked up still */
-#define FSCACHE_COOKIE_CREATING         1       /* T if non-index object being created still */
-#define FSCACHE_COOKIE_NO_DATA_YET      2       /* T if new object with no cached data yet */
-#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 */
-#define FSCACHE_COOKIE_INVALIDATING     7       /* T if cookie is being invalidated */
+#define FSCACHE_COOKIE_NO_DATA_YET      1       /* T if new object with no cached data yet */
+#define FSCACHE_COOKIE_UNAVAILABLE      2       /* T if cookie is unavailable (error, etc) */
+#define FSCACHE_COOKIE_INVALIDATING     3       /* T if cookie is being invalidated */
+#define FSCACHE_COOKIE_RELINQUISHED     4       /* T if cookie has been relinquished */
+#define FSCACHE_COOKIE_RETIRED          5       /* T if cookie was retired */
 };
 
 extern struct fscache_cookie fscache_fsdef_index;
@@ -341,45 +340,40 @@ extern struct fscache_cookie fscache_fsdef_index;
  * Event list for fscache_object::{event_mask,events}
  */
 enum {
-        FSCACHE_OBJECT_EV_REQUEUE,      /* T if object should be requeued */
+        FSCACHE_OBJECT_EV_NEW_CHILD,    /* T if object has a new child */
+        FSCACHE_OBJECT_EV_PARENT_READY, /* T if object's parent is ready */
         FSCACHE_OBJECT_EV_UPDATE,       /* T if object should be updated */
         FSCACHE_OBJECT_EV_INVALIDATE,   /* T if cache requested object invalidation */
         FSCACHE_OBJECT_EV_CLEARED,      /* T if accessors all gone */
         FSCACHE_OBJECT_EV_ERROR,        /* T if fatal error occurred during processing */
-        FSCACHE_OBJECT_EV_RELEASE,      /* T if netfs requested object release */
-        FSCACHE_OBJECT_EV_RETIRE,       /* T if netfs requested object retirement */
-        FSCACHE_OBJECT_EV_WITHDRAW,     /* T if cache requested object withdrawal */
+        FSCACHE_OBJECT_EV_KILL,         /* T if netfs relinquished or cache withdrew object */
         NR_FSCACHE_OBJECT_EVENTS
 };
 
 #define FSCACHE_OBJECT_EVENTS_MASK ((1UL << NR_FSCACHE_OBJECT_EVENTS) - 1)
 
 /*
+ * States for object state machine.
+ */
+struct fscache_transition {
+        unsigned long events;
+        const struct fscache_state *transit_to;
+};
+
+struct fscache_state {
+        char name[24];
+        char short_name[8];
+        const struct fscache_state *(*work)(struct fscache_object *object,
+                                            int event);
+        const struct fscache_transition transitions[];
+};
+
+/*
  * on-disk cache file or index handle
  */
 struct fscache_object {
-        enum fscache_object_state {
-                FSCACHE_OBJECT_INIT,            /* object in initial unbound state */
-                FSCACHE_OBJECT_LOOKING_UP,      /* looking up object */
-                FSCACHE_OBJECT_CREATING,        /* creating object */
-
-                /* active states */
-                FSCACHE_OBJECT_AVAILABLE,       /* cleaning up object after creation */
-                FSCACHE_OBJECT_ACTIVE,          /* object is usable */
-                FSCACHE_OBJECT_INVALIDATING,    /* object is invalidating */
-                FSCACHE_OBJECT_UPDATING,        /* object is updating */
-
-                /* terminal states */
-                FSCACHE_OBJECT_DYING,           /* object waiting for accessors to finish */
-                FSCACHE_OBJECT_LC_DYING,        /* object cleaning up after lookup/create */
-                FSCACHE_OBJECT_ABORT_INIT,      /* abort the init state */
-                FSCACHE_OBJECT_RELEASING,       /* releasing object */
-                FSCACHE_OBJECT_RECYCLING,       /* retiring object */
-                FSCACHE_OBJECT_WITHDRAWING,     /* withdrawing object */
-                FSCACHE_OBJECT_DEAD,            /* object is now dead */
-                FSCACHE_OBJECT__NSTATES
-        } state;
-
+        const struct fscache_state *state;      /* Object state machine state */
+        const struct fscache_transition *oob_table; /* OOB state transition table */
         int                     debug_id;       /* debugging ID */
         int                     n_children;     /* number of child objects */
         int                     n_ops;          /* number of extant ops on object */
@@ -390,6 +384,7 @@ struct fscache_object {
         spinlock_t              lock;           /* state and operations lock */
 
         unsigned long           lookup_jif;     /* time at which lookup started */
+        unsigned long           oob_event_mask; /* OOB events this object is interested in */
         unsigned long           event_mask;     /* events this object is interested in */
         unsigned long           events;         /* events to be processed by this object
                                                  * (order is important - using fls) */
@@ -398,6 +393,9 @@ struct fscache_object {
 #define FSCACHE_OBJECT_LOCK             0       /* T if object is busy being processed */
 #define FSCACHE_OBJECT_PENDING_WRITE    1       /* T if object has pending write */
 #define FSCACHE_OBJECT_WAITING          2       /* T if object is waiting on its parent */
+#define FSCACHE_OBJECT_IS_LIVE          3       /* T if object is not withdrawn or relinquished */
+#define FSCACHE_OBJECT_IS_LOOKED_UP     4       /* T if object has been looked up */
+#define FSCACHE_OBJECT_IS_AVAILABLE     5       /* T if object has become active */
 
         struct list_head        cache_link;     /* link in cache->object_list */
         struct hlist_node       cookie_link;    /* link in cookie->backing_objects */
@@ -415,62 +413,40 @@ struct fscache_object {
         loff_t                  store_limit_l;  /* current storage limit */
 };
 
-extern const char *fscache_object_states[];
+extern void fscache_object_init(struct fscache_object *, struct fscache_cookie *,
+                                struct fscache_cache *);
+extern void fscache_object_destroy(struct fscache_object *);
 
-#define fscache_object_is_active(obj)                         \
-        (!test_bit(FSCACHE_IOERROR, &(obj)->cache->flags) &&  \
-         (obj)->state >= FSCACHE_OBJECT_AVAILABLE &&          \
-         (obj)->state < FSCACHE_OBJECT_DYING)
+extern void fscache_object_lookup_negative(struct fscache_object *object);
+extern void fscache_obtained_object(struct fscache_object *object);
 
-#define fscache_object_is_dead(obj)                             \
-        (test_bit(FSCACHE_IOERROR, &(obj)->cache->flags) &&     \
-         (obj)->state >= FSCACHE_OBJECT_DYING)
+static inline bool fscache_object_is_live(struct fscache_object *object)
+{
+        return test_bit(FSCACHE_OBJECT_IS_LIVE, &object->flags);
+}
 
-extern void fscache_object_work_func(struct work_struct *work);
+static inline bool fscache_object_is_dying(struct fscache_object *object)
+{
+        return !fscache_object_is_live(object);
+}
 
-/**
- * fscache_object_init - Initialise a cache object description
- * @object: Object description
- *
- * Initialise a cache object description to its basic values.
- *
- * See Documentation/filesystems/caching/backend-api.txt for a complete
- * description.
- */
-static inline
-void fscache_object_init(struct fscache_object *object,
-                         struct fscache_cookie *cookie,
-                         struct fscache_cache *cache)
+static inline bool fscache_object_is_available(struct fscache_object *object)
 {
-        atomic_inc(&cache->object_count);
-
-        object->state = FSCACHE_OBJECT_INIT;
-        spin_lock_init(&object->lock);
-        INIT_LIST_HEAD(&object->cache_link);
-        INIT_HLIST_NODE(&object->cookie_link);
-        INIT_WORK(&object->work, fscache_object_work_func);
-        INIT_LIST_HEAD(&object->dependents);
-        INIT_LIST_HEAD(&object->dep_link);
-        INIT_LIST_HEAD(&object->pending_ops);
-        object->n_children = 0;
-        object->n_ops = object->n_in_progress = object->n_exclusive = 0;
-        object->events = object->event_mask = 0;
-        object->flags = 0;
-        object->store_limit = 0;
-        object->store_limit_l = 0;
-        object->cache = cache;
-        object->cookie = cookie;
-        object->parent = NULL;
+        return test_bit(FSCACHE_OBJECT_IS_AVAILABLE, &object->flags);
 }
 
-extern void fscache_object_lookup_negative(struct fscache_object *object);
-extern void fscache_obtained_object(struct fscache_object *object);
+static inline bool fscache_object_is_active(struct fscache_object *object)
+{
+        return fscache_object_is_available(object) &&
+                fscache_object_is_live(object) &&
+                !test_bit(FSCACHE_IOERROR, &object->cache->flags);
+}
 
-#ifdef CONFIG_FSCACHE_OBJECT_LIST
-extern void fscache_object_destroy(struct fscache_object *object);
-#else
-#define fscache_object_destroy(object) do {} while(0)
-#endif
+static inline bool fscache_object_is_dead(struct fscache_object *object)
+{
+        return fscache_object_is_dying(object) &&
+                test_bit(FSCACHE_IOERROR, &object->cache->flags);
+}
 
 /**
  * fscache_object_destroyed - Note destruction of an object in a cache
@@ -531,6 +507,33 @@ static inline void fscache_end_io(struct fscache_retrieval *op,
         op->end_io_func(page, op->context, error);
 }
 
+/**
+ * fscache_use_cookie - Request usage of cookie attached to an object
+ * @object: Object description
+ * 
+ * Request usage of the cookie attached to an object.  NULL is returned if the
+ * relinquishment had reduced the cookie usage count to 0.
+ */
+static inline bool fscache_use_cookie(struct fscache_object *object)
+{
+        struct fscache_cookie *cookie = object->cookie;
+        return atomic_inc_not_zero(&cookie->n_active) != 0;
+}
+
+/**
+ * fscache_unuse_cookie - Cease usage of cookie attached to an object
+ * @object: Object description
+ * 
+ * Cease usage of the cookie attached to an object.  When the users count
+ * reaches zero then the cookie relinquishment will be permitted to proceed.
+ */
+static inline void fscache_unuse_cookie(struct fscache_object *object)
+{
+        struct fscache_cookie *cookie = object->cookie;
+        if (atomic_dec_and_test(&cookie->n_active))
+                wake_up_atomic_t(&cookie->n_active);
+}
+
 /*
  * out-of-line cache backend functions
  */
diff --git a/include/linux/wait.h b/include/linux/wait.h
index 1133695eb067..f487a4750b7f 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -23,6 +23,7 @@ struct __wait_queue {
 struct wait_bit_key {
         void *flags;
         int bit_nr;
+#define WAIT_ATOMIC_T_BIT_NR -1
 };
 
 struct wait_bit_queue {
@@ -60,6 +61,9 @@ struct task_struct;
 #define __WAIT_BIT_KEY_INITIALIZER(word, bit)                           \
         { .flags = word, .bit_nr = bit, }
 
+#define __WAIT_ATOMIC_T_KEY_INITIALIZER(p)                              \
+        { .flags = p, .bit_nr = WAIT_ATOMIC_T_BIT_NR, }
+
 extern void __init_waitqueue_head(wait_queue_head_t *q, const char *name, struct lock_class_key *);
 
 #define init_waitqueue_head(q)                          \
@@ -146,8 +150,10 @@ void __wake_up_bit(wait_queue_head_t *, void *, int);
 int __wait_on_bit(wait_queue_head_t *, struct wait_bit_queue *, int (*)(void *), unsigned);
 int __wait_on_bit_lock(wait_queue_head_t *, struct wait_bit_queue *, int (*)(void *), unsigned);
 void wake_up_bit(void *, int);
+void wake_up_atomic_t(atomic_t *);
 int out_of_line_wait_on_bit(void *, int, int (*)(void *), unsigned);
 int out_of_line_wait_on_bit_lock(void *, int, int (*)(void *), unsigned);
+int out_of_line_wait_on_atomic_t(atomic_t *, int (*)(atomic_t *), unsigned);
 wait_queue_head_t *bit_waitqueue(void *, int);
 
 #define wake_up(x)                      __wake_up(x, TASK_NORMAL, 1, NULL)
@@ -902,5 +908,23 @@ static inline int wait_on_bit_lock(void *word, int bit,
                 return 0;
         return out_of_line_wait_on_bit_lock(word, bit, action, mode);
 }
+
+/**
+ * wait_on_atomic_t - Wait for an atomic_t to become 0
+ * @val: The atomic value being waited on, a kernel virtual address
+ * @action: the function used to sleep, which may take special actions
+ * @mode: the task state to sleep in
+ *
+ * Wait for an atomic_t to become 0.  We abuse the bit-wait waitqueue table for
+ * the purpose of getting a waitqueue, but we set the key to a bit number
+ * outside of the target 'word'.
+ */
+static inline
+int wait_on_atomic_t(atomic_t *val, int (*action)(atomic_t *), unsigned mode)
+{
+        if (atomic_read(val) == 0)
+                return 0;
+        return out_of_line_wait_on_atomic_t(val, action, mode);
+}
         
 #endif