bcache: Fix, improve efficiency of closure_sync()

Eliminates cases where sync can race and fail to complete / get stuck.
Removes many status flags and simplifies entering-and-exiting closure
sleeping behaviors.

[mlyle: fixed conflicts due to changed return behavior in mainline.
extended commit comment, and squashed down two commits that were mostly
contradictory to get to this state.  Changed __set_current_state to
set_current_state per Jens review comment]

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Michael Lyle <mlyle@lyle.org>
Reviewed-by: Michael Lyle <mlyle@lyle.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/md/bcache/closure.c b/drivers/md/bcache/closure.c
index 1841d03..ca7ace6 100644 (file)
--- a/drivers/md/bcache/closure.c
+++ b/drivers/md/bcache/closure.c
@@ -18,10 +18,6 @@ static inline void closure_put_after_sub(struct closure *cl, int flags)
        BUG_ON(flags & CLOSURE_GUARD_MASK);
        BUG_ON(!r && (flags & ~CLOSURE_DESTRUCTOR));
 
-       /* Must deliver precisely one wakeup */
-       if (r == 1 && (flags & CLOSURE_SLEEPING))
-               wake_up_process(cl->task);
-
        if (!r) {
                if (cl->fn && !(flags & CLOSURE_DESTRUCTOR)) {
                        atomic_set(&cl->remaining,
@@ -100,28 +96,34 @@ bool closure_wait(struct closure_waitlist *waitlist, struct closure *cl)
 }
 EXPORT_SYMBOL(closure_wait);
 
-/**
- * closure_sync - sleep until a closure has nothing left to wait on
- *
- * Sleeps until the refcount hits 1 - the thread that's running the closure owns
- * the last refcount.
- */
-void closure_sync(struct closure *cl)
+struct closure_syncer {
+       struct task_struct      *task;
+       int                     done;
+};
+
+static void closure_sync_fn(struct closure *cl)
 {
-       while (1) {
-               __closure_start_sleep(cl);
-               closure_set_ret_ip(cl);
+       cl->s->done = 1;
+       wake_up_process(cl->s->task);
+}
 
-               if ((atomic_read(&cl->remaining) &
-                    CLOSURE_REMAINING_MASK) == 1)
-                       break;
+void __closure_sync(struct closure *cl)
+{
+       struct closure_syncer s = { .task = current };
 
+       cl->s = &s;
+       continue_at(cl, closure_sync_fn, NULL);
+
+       while (1) {
+               set_current_state(TASK_UNINTERRUPTIBLE);
+               if (s.done)
+                       break;
                schedule();
        }
 
-       __closure_end_sleep(cl);
+       __set_current_state(TASK_RUNNING);
 }
-EXPORT_SYMBOL(closure_sync);
+EXPORT_SYMBOL(__closure_sync);
 
 #ifdef CONFIG_BCACHE_CLOSURES_DEBUG
 
@@ -168,12 +170,10 @@ static int debug_seq_show(struct seq_file *f, void *data)
                           cl, (void *) cl->ip, cl->fn, cl->parent,
                           r & CLOSURE_REMAINING_MASK);
 
-               seq_printf(f, "%s%s%s%s\n",
+               seq_printf(f, "%s%s\n",
                           test_bit(WORK_STRUCT_PENDING_BIT,
                                    work_data_bits(&cl->work)) ? "Q" : "",
-                          r & CLOSURE_RUNNING  ? "R" : "",
-                          r & CLOSURE_STACK    ? "S" : "",
-                          r & CLOSURE_SLEEPING ? "Sl" : "");
+                          r & CLOSURE_RUNNING  ? "R" : "");
 
                if (r & CLOSURE_WAITING)
                        seq_printf(f, " W %pF\n",

diff --git a/drivers/md/bcache/closure.h b/drivers/md/bcache/closure.h
index ccfbea6..392a87c 100644 (file)
--- a/drivers/md/bcache/closure.h
+++ b/drivers/md/bcache/closure.h
@@ -103,6 +103,7 @@
  */
 
 struct closure;
+struct closure_syncer;
 typedef void (closure_fn) (struct closure *);
 
 struct closure_waitlist {
@@ -115,10 +116,6 @@ enum closure_state {
         * the thread that owns the closure, and cleared by the thread that's
         * waking up the closure.
         *
-        * CLOSURE_SLEEPING: Must be set before a thread uses a closure to sleep
-        * - indicates that cl->task is valid and closure_put() may wake it up.
-        * Only set or cleared by the thread that owns the closure.
-        *
         * The rest are for debugging and don't affect behaviour:
         *
         * CLOSURE_RUNNING: Set when a closure is running (i.e. by
@@ -128,22 +125,16 @@ enum closure_state {
         * continue_at() and closure_return() clear it for you, if you're doing
         * something unusual you can use closure_set_dead() which also helps
         * annotate where references are being transferred.
-        *
-        * CLOSURE_STACK: Sanity check - remaining should never hit 0 on a
-        * closure with this flag set
         */
 
-       CLOSURE_BITS_START      = (1 << 23),
-       CLOSURE_DESTRUCTOR      = (1 << 23),
-       CLOSURE_WAITING         = (1 << 25),
-       CLOSURE_SLEEPING        = (1 << 27),
-       CLOSURE_RUNNING         = (1 << 29),
-       CLOSURE_STACK           = (1 << 31),
+       CLOSURE_BITS_START      = (1U << 27),
+       CLOSURE_DESTRUCTOR      = (1U << 27),
+       CLOSURE_WAITING         = (1U << 29),
+       CLOSURE_RUNNING         = (1U << 31),
 };
 
 #define CLOSURE_GUARD_MASK                                     \
-       ((CLOSURE_DESTRUCTOR|CLOSURE_WAITING|CLOSURE_SLEEPING|  \
-         CLOSURE_RUNNING|CLOSURE_STACK) << 1)
+       ((CLOSURE_DESTRUCTOR|CLOSURE_WAITING|CLOSURE_RUNNING) << 1)
 
 #define CLOSURE_REMAINING_MASK         (CLOSURE_BITS_START - 1)
 #define CLOSURE_REMAINING_INITIALIZER  (1|CLOSURE_RUNNING)
@@ -152,7 +143,7 @@ struct closure {
        union {
                struct {
                        struct workqueue_struct *wq;
-                       struct task_struct      *task;
+                       struct closure_syncer   *s;
                        struct llist_node       list;
                        closure_fn              *fn;
                };
@@ -178,7 +169,19 @@ void closure_sub(struct closure *cl, int v);
 void closure_put(struct closure *cl);
 void __closure_wake_up(struct closure_waitlist *list);
 bool closure_wait(struct closure_waitlist *list, struct closure *cl);
-void closure_sync(struct closure *cl);
+void __closure_sync(struct closure *cl);
+
+/**
+ * closure_sync - sleep until a closure a closure has nothing left to wait on
+ *
+ * Sleeps until the refcount hits 1 - the thread that's running the closure owns
+ * the last refcount.
+ */
+static inline void closure_sync(struct closure *cl)
+{
+       if ((atomic_read(&cl->remaining) & CLOSURE_REMAINING_MASK) != 1)
+               __closure_sync(cl);
+}
 
 #ifdef CONFIG_BCACHE_CLOSURES_DEBUG
 
@@ -215,24 +218,6 @@ static inline void closure_set_waiting(struct closure *cl, unsigned long f)
 #endif
 }
 
-static inline void __closure_end_sleep(struct closure *cl)
-{
-       __set_current_state(TASK_RUNNING);
-
-       if (atomic_read(&cl->remaining) & CLOSURE_SLEEPING)
-               atomic_sub(CLOSURE_SLEEPING, &cl->remaining);
-}
-
-static inline void __closure_start_sleep(struct closure *cl)
-{
-       closure_set_ip(cl);
-       cl->task = current;
-       set_current_state(TASK_UNINTERRUPTIBLE);
-
-       if (!(atomic_read(&cl->remaining) & CLOSURE_SLEEPING))
-               atomic_add(CLOSURE_SLEEPING, &cl->remaining);
-}
-
 static inline void closure_set_stopped(struct closure *cl)
 {
        atomic_sub(CLOSURE_RUNNING, &cl->remaining);
@@ -241,7 +226,6 @@ static inline void closure_set_stopped(struct closure *cl)
 static inline void set_closure_fn(struct closure *cl, closure_fn *fn,
                                  struct workqueue_struct *wq)
 {
-       BUG_ON(object_is_on_stack(cl));
        closure_set_ip(cl);
        cl->fn = fn;
        cl->wq = wq;
@@ -300,7 +284,7 @@ static inline void closure_init(struct closure *cl, struct closure *parent)
 static inline void closure_init_stack(struct closure *cl)
 {
        memset(cl, 0, sizeof(struct closure));
-       atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER|CLOSURE_STACK);
+       atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER);
 }
 
 /**
@@ -322,6 +306,8 @@ static inline void closure_wake_up(struct closure_waitlist *list)
  * This is because after calling continue_at() you no longer have a ref on @cl,
  * and whatever @cl owns may be freed out from under you - a running closure fn
  * has a ref on its own closure which continue_at() drops.
+ *
+ * Note you are expected to immediately return after using this macro.
  */
 #define continue_at(_cl, _fn, _wq)                                     \
 do {                                                                   \