1 files changed, 66 insertions, 74 deletions

diff --git a/fs/direct-io.c b/fs/direct-io.c
index b296942..bc1cbf9 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -121,9 +121,8 @@ struct dio {
 	int page_errors;		/* errno from get_user_pages() */
 
 	/* BIO completion state */
+	atomic_t refcount;		/* direct_io_worker() and bios */
 	spinlock_t bio_lock;		/* protects BIO fields below */
-	int bio_count;			/* nr bios to be completed */
-	int bios_in_flight;		/* nr bios in flight */
 	struct bio *bio_list;		/* singly linked via bi_private */
 	struct task_struct *waiter;	/* waiting task (NULL if none) */
 
@@ -256,44 +255,27 @@ static int dio_complete(struct dio *dio, loff_t offset, int ret)
  * Called when a BIO has been processed.  If the count goes to zero then IO is
  * complete and we can signal this to the AIO layer.
  */
-static void finished_one_bio(struct dio *dio)
+static void dio_complete_aio(struct dio *dio)
 {
 	unsigned long flags;
+	int ret;
 
-	spin_lock_irqsave(&dio->bio_lock, flags);
-	if (dio->bio_count == 1) {
-		if (dio->is_async) {
-			int ret;
-
-			/*
-			 * Last reference to the dio is going away.
-			 * Drop spinlock and complete the DIO.
-			 */
-			spin_unlock_irqrestore(&dio->bio_lock, flags);
-
-			ret = dio_complete(dio, dio->iocb->ki_pos, 0);
+	ret = dio_complete(dio, dio->iocb->ki_pos, 0);
 
-			/* Complete AIO later if falling back to buffered i/o */
-			if (dio->result == dio->size ||
-				((dio->rw == READ) && dio->result)) {
-				aio_complete(dio->iocb, ret, 0);
-				kfree(dio);
-				return;
-			} else {
-				/*
-				 * Falling back to buffered
-				 */
-				spin_lock_irqsave(&dio->bio_lock, flags);
-				dio->bio_count--;
-				if (dio->waiter)
-					wake_up_process(dio->waiter);
-				spin_unlock_irqrestore(&dio->bio_lock, flags);
-				return;
-			}
-		}
+	/* Complete AIO later if falling back to buffered i/o */
+	if (dio->result == dio->size ||
+		((dio->rw == READ) && dio->result)) {
+		aio_complete(dio->iocb, ret, 0);
+		kfree(dio);
+	} else {
+		/*
+		 * Falling back to buffered
+		 */
+		spin_lock_irqsave(&dio->bio_lock, flags);
+		if (dio->waiter)
+			wake_up_process(dio->waiter);
+		spin_unlock_irqrestore(&dio->bio_lock, flags);
 	}
-	dio->bio_count--;
-	spin_unlock_irqrestore(&dio->bio_lock, flags);
 }
 
 static int dio_bio_complete(struct dio *dio, struct bio *bio);
@@ -309,6 +291,10 @@ static int dio_bio_end_aio(struct bio *bio, unsigned int bytes_done, int error)
 
 	/* cleanup the bio */
 	dio_bio_complete(dio, bio);
+
+	if (atomic_dec_and_test(&dio->refcount))
+		dio_complete_aio(dio);
+
 	return 0;
 }
 
@@ -330,8 +316,7 @@ static int dio_bio_end_io(struct bio *bio, unsigned int bytes_done, int error)
 	spin_lock_irqsave(&dio->bio_lock, flags);
 	bio->bi_private = dio->bio_list;
 	dio->bio_list = bio;
-	dio->bios_in_flight--;
-	if (dio->waiter && dio->bios_in_flight == 0)
+	if ((atomic_sub_return(1, &dio->refcount) == 1) && dio->waiter)
 		wake_up_process(dio->waiter);
 	spin_unlock_irqrestore(&dio->bio_lock, flags);
 	return 0;
@@ -362,17 +347,15 @@ dio_bio_alloc(struct dio *dio, struct block_device *bdev,
  * In the AIO read case we speculatively dirty the pages before starting IO.
  * During IO completion, any of these pages which happen to have been written
  * back will be redirtied by bio_check_pages_dirty().
+ *
+ * bios hold a dio reference between submit_bio and ->end_io.
  */
 static void dio_bio_submit(struct dio *dio)
 {
 	struct bio *bio = dio->bio;
-	unsigned long flags;
 
 	bio->bi_private = dio;
-	spin_lock_irqsave(&dio->bio_lock, flags);
-	dio->bio_count++;
-	dio->bios_in_flight++;
-	spin_unlock_irqrestore(&dio->bio_lock, flags);
+	atomic_inc(&dio->refcount);
 	if (dio->is_async && dio->rw == READ)
 		bio_set_pages_dirty(bio);
 	submit_bio(dio->rw, bio);
@@ -390,18 +373,28 @@ static void dio_cleanup(struct dio *dio)
 		page_cache_release(dio_get_page(dio));
 }
 
+static int wait_for_more_bios(struct dio *dio)
+{
+	assert_spin_locked(&dio->bio_lock);
+
+	return (atomic_read(&dio->refcount) > 1) && (dio->bio_list == NULL);
+}
+
 /*
- * Wait for the next BIO to complete.  Remove it and return it.
+ * Wait for the next BIO to complete.  Remove it and return it.  NULL is
+ * returned once all BIOs have been completed.  This must only be called once
+ * all bios have been issued so that dio->refcount can only decrease.  This
+ * requires that that the caller hold a reference on the dio.
  */
 static struct bio *dio_await_one(struct dio *dio)
 {
 	unsigned long flags;
-	struct bio *bio;
+	struct bio *bio = NULL;
 
 	spin_lock_irqsave(&dio->bio_lock, flags);
-	while (dio->bio_list == NULL) {
+	while (wait_for_more_bios(dio)) {
 		set_current_state(TASK_UNINTERRUPTIBLE);
-		if (dio->bio_list == NULL) {
+		if (wait_for_more_bios(dio)) {
 			dio->waiter = current;
 			spin_unlock_irqrestore(&dio->bio_lock, flags);
 			io_schedule();
@@ -410,8 +403,10 @@ static struct bio *dio_await_one(struct dio *dio)
 		}
 		set_current_state(TASK_RUNNING);
 	}
-	bio = dio->bio_list;
-	dio->bio_list = bio->bi_private;
+	if (dio->bio_list) {
+		bio = dio->bio_list;
+		dio->bio_list = bio->bi_private;
+	}
 	spin_unlock_irqrestore(&dio->bio_lock, flags);
 	return bio;
 }
@@ -440,25 +435,24 @@ static int dio_bio_complete(struct dio *dio, struct bio *bio)
 		}
 		bio_put(bio);
 	}
-	finished_one_bio(dio);
 	return uptodate ? 0 : -EIO;
 }
 
 /*
- * Wait on and process all in-flight BIOs.
+ * Wait on and process all in-flight BIOs.  This must only be called once
+ * all bios have been issued so that the refcount can only decrease.
+ * This just waits for all bios to make it through dio_bio_complete.  IO
+ * errors are propogated through dio->io_error and should be propogated via
+ * dio_complete().
  */
 static void dio_await_completion(struct dio *dio)
 {
-	/*
-	 * The bio_lock is not held for the read of bio_count.
-	 * This is ok since it is the dio_bio_complete() that changes
-	 * bio_count.
-	 */
-	while (dio->bio_count) {
-		struct bio *bio = dio_await_one(dio);
-		/* io errors are propogated through dio->io_error */
-		dio_bio_complete(dio, bio);
-	}
+	struct bio *bio;
+	do {
+		bio = dio_await_one(dio);
+		if (bio)
+			dio_bio_complete(dio, bio);
+	} while (bio);
 }
 
 /*
@@ -995,16 +989,7 @@ direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode,
 	dio->iocb = iocb;
 	dio->i_size = i_size_read(inode);
 
-	/*
-	 * BIO completion state.
-	 *
-	 * ->bio_count starts out at one, and we decrement it to zero after all
-	 * BIOs are submitted.  This to avoid the situation where a really fast
-	 * (or synchronous) device could take the count to zero while we're
-	 * still submitting BIOs.
-	 */
-	dio->bio_count = 1;
-	dio->bios_in_flight = 0;
+	atomic_set(&dio->refcount, 1);
 	spin_lock_init(&dio->bio_lock);
 	dio->bio_list = NULL;
 	dio->waiter = NULL;
@@ -1111,7 +1096,11 @@ direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode,
 		}
 		if (ret == 0)
 			ret = dio->result;
-		finished_one_bio(dio);		/* This can free the dio */
+
+		/* this can free the dio */
+		if (atomic_dec_and_test(&dio->refcount))
+			dio_complete_aio(dio);
+
 		if (should_wait) {
 			unsigned long flags;
 			/*
@@ -1122,7 +1111,7 @@ direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode,
 
 			spin_lock_irqsave(&dio->bio_lock, flags);
 			set_current_state(TASK_UNINTERRUPTIBLE);
-			while (dio->bio_count) {
+			while (atomic_read(&dio->refcount)) {
 				spin_unlock_irqrestore(&dio->bio_lock, flags);
 				io_schedule();
 				spin_lock_irqsave(&dio->bio_lock, flags);
@@ -1133,7 +1122,6 @@ direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode,
 			kfree(dio);
 		}
 	} else {
-		finished_one_bio(dio);
 		dio_await_completion(dio);
 
 		ret = dio_complete(dio, offset, ret);
@@ -1146,7 +1134,11 @@ direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode,
 			 * i/o, we have to mark the the aio complete.
 			 */
 			aio_complete(iocb, ret, 0);
-		kfree(dio);
+
+		if (atomic_dec_and_test(&dio->refcount))
+			kfree(dio);
+		else
+			BUG();
 	}
 	return ret;
 }