1 files changed, 76 insertions, 89 deletions

diff --git a/fs/direct-io.c b/fs/direct-io.c
index b912270942f..e82adc2debb 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -53,13 +53,6 @@
  *
  * If blkfactor is zero then the user's request was aligned to the filesystem's
  * blocksize.
- *
- * lock_type is DIO_LOCKING for regular files on direct-IO-naive filesystems.
- * This determines whether we need to do the fancy locking which prevents
- * direct-IO from being able to read uninitialised disk blocks.  If its zero
- * (blockdev) this locking is not done, and if it is DIO_OWN_LOCKING i_mutex is
- * not held for the entire direct write (taken briefly, initially, during a
- * direct read though, but its never held for the duration of a direct-IO).
  */
 
 struct dio {
@@ -68,7 +61,7 @@ struct dio {
 	struct inode *inode;
 	int rw;
 	loff_t i_size;			/* i_size when submitted */
-	int lock_type;			/* doesn't change */
+	int flags;			/* doesn't change */
 	unsigned blkbits;		/* doesn't change */
 	unsigned blkfactor;		/* When we're using an alignment which
 					   is finer than the filesystem's soft
@@ -104,6 +97,18 @@ struct dio {
 	unsigned cur_page_len;		/* Nr of bytes at cur_page_offset */
 	sector_t cur_page_block;	/* Where it starts */
 
+	/* BIO completion state */
+	spinlock_t bio_lock;		/* protects BIO fields below */
+	unsigned long refcount;		/* direct_io_worker() and bios */
+	struct bio *bio_list;		/* singly linked via bi_private */
+	struct task_struct *waiter;	/* waiting task (NULL if none) */
+
+	/* AIO related stuff */
+	struct kiocb *iocb;		/* kiocb */
+	int is_async;			/* is IO async ? */
+	int io_error;			/* IO error in completion path */
+	ssize_t result;                 /* IO result */
+
 	/*
 	 * Page fetching state. These variables belong to dio_refill_pages().
 	 */
@@ -115,22 +120,16 @@ struct dio {
 	 * Page queue.  These variables belong to dio_refill_pages() and
 	 * dio_get_page().
 	 */
-	struct page *pages[DIO_PAGES];	/* page buffer */
 	unsigned head;			/* next page to process */
 	unsigned tail;			/* last valid page + 1 */
 	int page_errors;		/* errno from get_user_pages() */
 
-	/* BIO completion state */
-	spinlock_t bio_lock;		/* protects BIO fields below */
-	unsigned long refcount;		/* direct_io_worker() and bios */
-	struct bio *bio_list;		/* singly linked via bi_private */
-	struct task_struct *waiter;	/* waiting task (NULL if none) */
-
-	/* AIO related stuff */
-	struct kiocb *iocb;		/* kiocb */
-	int is_async;			/* is IO async ? */
-	int io_error;			/* IO error in completion path */
-	ssize_t result;                 /* IO result */
+	/*
+	 * pages[] (and any fields placed after it) are not zeroed out at
+	 * allocation time.  Don't add new fields after pages[] unless you
+	 * wish that they not be zeroed.
+	 */
+	struct page *pages[DIO_PAGES];	/* page buffer */
 };
 
 /*
@@ -240,7 +239,8 @@ static int dio_complete(struct dio *dio, loff_t offset, int ret)
 	if (dio->end_io && dio->result)
 		dio->end_io(dio->iocb, offset, transferred,
 			    dio->map_bh.b_private);
-	if (dio->lock_type == DIO_LOCKING)
+
+	if (dio->flags & DIO_LOCKING)
 		/* lockdep: non-owner release */
 		up_read_non_owner(&dio->inode->i_alloc_sem);
 
@@ -515,21 +515,24 @@ static int get_more_blocks(struct dio *dio)
 		map_bh->b_state = 0;
 		map_bh->b_size = fs_count << dio->inode->i_blkbits;
 
+		/*
+		 * For writes inside i_size on a DIO_SKIP_HOLES filesystem we
+		 * forbid block creations: only overwrites are permitted.
+		 * We will return early to the caller once we see an
+		 * unmapped buffer head returned, and the caller will fall
+		 * back to buffered I/O.
+		 *
+		 * Otherwise the decision is left to the get_blocks method,
+		 * which may decide to handle it or also return an unmapped
+		 * buffer head.
+		 */
 		create = dio->rw & WRITE;
-		if (dio->lock_type == DIO_LOCKING) {
+		if (dio->flags & DIO_SKIP_HOLES) {
 			if (dio->block_in_file < (i_size_read(dio->inode) >>
 							dio->blkbits))
 				create = 0;
-		} else if (dio->lock_type == DIO_NO_LOCKING) {
-			create = 0;
 		}
 
-		/*
-		 * For writes inside i_size we forbid block creations: only
-		 * overwrites are permitted.  We fall back to buffered writes
-		 * at a higher level for inside-i_size block-instantiating
-		 * writes.
-		 */
 		ret = (*dio->get_block)(dio->inode, fs_startblk,
 						map_bh, create);
 	}
@@ -1039,7 +1042,7 @@ direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode,
 	 * we can let i_mutex go now that its achieved its purpose
 	 * of protecting us from looking up uninitialized blocks.
 	 */
-	if ((rw == READ) && (dio->lock_type == DIO_LOCKING))
+	if (rw == READ && (dio->flags & DIO_LOCKING))
 		mutex_unlock(&dio->inode->i_mutex);
 
 	/*
@@ -1086,30 +1089,28 @@ direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode,
 
 /*
  * This is a library function for use by filesystem drivers.
- * The locking rules are governed by the dio_lock_type parameter.
  *
- * DIO_NO_LOCKING (no locking, for raw block device access)
- * For writes, i_mutex is not held on entry; it is never taken.
+ * The locking rules are governed by the flags parameter:
+ *  - if the flags value contains DIO_LOCKING we use a fancy locking
+ *    scheme for dumb filesystems.
+ *    For writes this function is called under i_mutex and returns with
+ *    i_mutex held, for reads, i_mutex is not held on entry, but it is
+ *    taken and dropped again before returning.
+ *    For reads and writes i_alloc_sem is taken in shared mode and released
+ *    on I/O completion (which may happen asynchronously after returning to
+ *    the caller).
  *
- * DIO_LOCKING (simple locking for regular files)
- * For writes we are called under i_mutex and return with i_mutex held, even
- * though it is internally dropped.
- * For reads, i_mutex is not held on entry, but it is taken and dropped before
- * returning.
- *
- * DIO_OWN_LOCKING (filesystem provides synchronisation and handling of
- *	uninitialised data, allowing parallel direct readers and writers)
- * For writes we are called without i_mutex, return without it, never touch it.
- * For reads we are called under i_mutex and return with i_mutex held, even
- * though it may be internally dropped.
- *
- * Additional i_alloc_sem locking requirements described inline below.
+ *  - if the flags value does NOT contain DIO_LOCKING we don't use any
+ *    internal locking but rather rely on the filesystem to synchronize
+ *    direct I/O reads/writes versus each other and truncate.
+ *    For reads and writes both i_mutex and i_alloc_sem are not held on
+ *    entry and are never taken.
  */
 ssize_t
 __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
 	struct block_device *bdev, const struct iovec *iov, loff_t offset, 
 	unsigned long nr_segs, get_block_t get_block, dio_iodone_t end_io,
-	int dio_lock_type)
+	int flags)
 {
 	int seg;
 	size_t size;
@@ -1120,8 +1121,6 @@ __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
 	ssize_t retval = -EINVAL;
 	loff_t end = offset;
 	struct dio *dio;
-	int release_i_mutex = 0;
-	int acquire_i_mutex = 0;
 
 	if (rw & WRITE)
 		rw = WRITE_ODIRECT_PLUG;
@@ -1151,48 +1150,41 @@ __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
 		}
 	}
 
-	dio = kzalloc(sizeof(*dio), GFP_KERNEL);
+	dio = kmalloc(sizeof(*dio), GFP_KERNEL);
 	retval = -ENOMEM;
 	if (!dio)
 		goto out;
-
 	/*
-	 * For block device access DIO_NO_LOCKING is used,
-	 *	neither readers nor writers do any locking at all
-	 * For regular files using DIO_LOCKING,
-	 *	readers need to grab i_mutex and i_alloc_sem
-	 *	writers need to grab i_alloc_sem only (i_mutex is already held)
-	 * For regular files using DIO_OWN_LOCKING,
-	 *	neither readers nor writers take any locks here
+	 * Believe it or not, zeroing out the page array caused a .5%
+	 * performance regression in a database benchmark.  So, we take
+	 * care to only zero out what's needed.
 	 */
-	dio->lock_type = dio_lock_type;
-	if (dio_lock_type != DIO_NO_LOCKING) {
+	memset(dio, 0, offsetof(struct dio, pages));
+
+	dio->flags = flags;
+	if (dio->flags & DIO_LOCKING) {
 		/* watch out for a 0 len io from a tricksy fs */
 		if (rw == READ && end > offset) {
-			struct address_space *mapping;
+			struct address_space *mapping =
+					iocb->ki_filp->f_mapping;
 
-			mapping = iocb->ki_filp->f_mapping;
-			if (dio_lock_type != DIO_OWN_LOCKING) {
-				mutex_lock(&inode->i_mutex);
-				release_i_mutex = 1;
-			}
+			/* will be released by direct_io_worker */
+			mutex_lock(&inode->i_mutex);
 
 			retval = filemap_write_and_wait_range(mapping, offset,
 							      end - 1);
 			if (retval) {
+				mutex_unlock(&inode->i_mutex);
 				kfree(dio);
 				goto out;
 			}
-
-			if (dio_lock_type == DIO_OWN_LOCKING) {
-				mutex_unlock(&inode->i_mutex);
-				acquire_i_mutex = 1;
-			}
 		}
 
-		if (dio_lock_type == DIO_LOCKING)
-			/* lockdep: not the owner will release it */
-			down_read_non_owner(&inode->i_alloc_sem);
+		/*
+		 * Will be released at I/O completion, possibly in a
+		 * different thread.
+		 */
+		down_read_non_owner(&inode->i_alloc_sem);
 	}
 
 	/*
@@ -1210,24 +1202,19 @@ __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
 	/*
 	 * In case of error extending write may have instantiated a few
 	 * blocks outside i_size. Trim these off again for DIO_LOCKING.
-	 * NOTE: DIO_NO_LOCK/DIO_OWN_LOCK callers have to handle this by
-	 * it's own meaner.
+	 *
+	 * NOTE: filesystems with their own locking have to handle this
+	 * on their own.
 	 */
-	if (unlikely(retval < 0 && (rw & WRITE))) {
-		loff_t isize = i_size_read(inode);
-
-		if (end > isize && dio_lock_type == DIO_LOCKING)
-			vmtruncate(inode, isize);
+	if (flags & DIO_LOCKING) {
+		if (unlikely((rw & WRITE) && retval < 0)) {
+			loff_t isize = i_size_read(inode);
+			if (end > isize)
+				vmtruncate(inode, isize);
+		}
 	}
 
-	if (rw == READ && dio_lock_type == DIO_LOCKING)
-		release_i_mutex = 0;
-
 out:
-	if (release_i_mutex)
-		mutex_unlock(&inode->i_mutex);
-	else if (acquire_i_mutex)
-		mutex_lock(&inode->i_mutex);
 	return retval;
 }
 EXPORT_SYMBOL(__blockdev_direct_IO);