Merge branch 'block-dev'

Merge 'block-dev' branch.

I was going to just mark everything here for stable and leave it to the
3.8 merge window, but having decided on doing another -rc, I migth as
well merge it now.

This removes the bd_block_size_semaphore semaphore that was added in
this release to fix a race condition between block size changes and
block IO, and replaces it with atomicity guaratees in fs/buffer.c
instead, along with simplifying fs/block-dev.c.

This removes more lines than it adds, makes the code generally simpler,
and avoids the latency/rt issues that the block size semaphore
introduced for mount.

I'm not happy with the timing, but it wouldn't be much better doing this
during the merge window and then having some delayed back-port of it
into stable.

* block-dev:
blkdev_max_block: make private to fs/buffer.c
direct-io: don't read inode->i_blkbits multiple times
blockdev: remove bd_block_size_semaphore again
fs/buffer.c: make block-size be per-page and protected by the page lock

drivers/char/raw.c

···
 
 static const struct file_operations raw_fops = {
 	.read		= do_sync_read,
-	.aio_read	= blkdev_aio_read,
+	.aio_read	= generic_file_aio_read,
 	.write		= do_sync_write,
 	.aio_write	= blkdev_aio_write,
 	.fsync		= blkdev_fsync,

fs/block_dev.c

···
 	spin_unlock(&dst->wb.list_lock);
 }
 
-sector_t blkdev_max_block(struct block_device *bdev)
-{
-	sector_t retval = ~((sector_t)0);
-	loff_t sz = i_size_read(bdev->bd_inode);
-
-	if (sz) {
-		unsigned int size = block_size(bdev);
-		unsigned int sizebits = blksize_bits(size);
-		retval = (sz >> sizebits);
-	}
-	return retval;
-}
-
 /* Kill _all_ buffers and pagecache , dirty or not.. */
 void kill_bdev(struct block_device *bdev)
 {
···
 
 int set_blocksize(struct block_device *bdev, int size)
 {
-	struct address_space *mapping;
-
 	/* Size must be a power of two, and between 512 and PAGE_SIZE */
 	if (size > PAGE_SIZE || size < 512 || !is_power_of_2(size))
 		return -EINVAL;
···
 	if (size < bdev_logical_block_size(bdev))
 		return -EINVAL;
 
-	/* Prevent starting I/O or mapping the device */
-	percpu_down_write(&bdev->bd_block_size_semaphore);
-
-	/* Check that the block device is not memory mapped */
-	mapping = bdev->bd_inode->i_mapping;
-	mutex_lock(&mapping->i_mmap_mutex);
-	if (mapping_mapped(mapping)) {
-		mutex_unlock(&mapping->i_mmap_mutex);
-		percpu_up_write(&bdev->bd_block_size_semaphore);
-		return -EBUSY;
-	}
-	mutex_unlock(&mapping->i_mmap_mutex);
-
 	/* Don't change the size if it is same as current */
 	if (bdev->bd_block_size != size) {
 		sync_blockdev(bdev);
···
 		bdev->bd_inode->i_blkbits = blksize_bits(size);
 		kill_bdev(bdev);
 	}
-
-	percpu_up_write(&bdev->bd_block_size_semaphore);
-
 	return 0;
 }
 
···
 blkdev_get_block(struct inode *inode, sector_t iblock,
 		struct buffer_head *bh, int create)
 {
-	if (iblock >= blkdev_max_block(I_BDEV(inode))) {
-		if (create)
-			return -EIO;
-
-		/*
-		 * for reads, we're just trying to fill a partial page.
-		 * return a hole, they will have to call get_block again
-		 * before they can fill it, and they will get -EIO at that
-		 * time
-		 */
-		return 0;
-	}
 	bh->b_bdev = I_BDEV(inode);
 	bh->b_blocknr = iblock;
 	set_buffer_mapped(bh);
-	return 0;
-}
-
-static int
-blkdev_get_blocks(struct inode *inode, sector_t iblock,
-		struct buffer_head *bh, int create)
-{
-	sector_t end_block = blkdev_max_block(I_BDEV(inode));
-	unsigned long max_blocks = bh->b_size >> inode->i_blkbits;
-
-	if ((iblock + max_blocks) > end_block) {
-		max_blocks = end_block - iblock;
-		if ((long)max_blocks <= 0) {
-			if (create)
-				return -EIO;	/* write fully beyond EOF */
-			/*
-			 * It is a read which is fully beyond EOF.  We return
-			 * a !buffer_mapped buffer
-			 */
-			max_blocks = 0;
-		}
-	}
-
-	bh->b_bdev = I_BDEV(inode);
-	bh->b_blocknr = iblock;
-	bh->b_size = max_blocks << inode->i_blkbits;
-	if (max_blocks)
-		set_buffer_mapped(bh);
 	return 0;
 }
 
···
 	struct inode *inode = file->f_mapping->host;
 
 	return __blockdev_direct_IO(rw, iocb, inode, I_BDEV(inode), iov, offset,
-				    nr_segs, blkdev_get_blocks, NULL, NULL, 0);
+				    nr_segs, blkdev_get_block, NULL, NULL, 0);
 }
 
 int __sync_blockdev(struct block_device *bdev, int wait)
···
 	struct bdev_inode *ei = kmem_cache_alloc(bdev_cachep, GFP_KERNEL);
 	if (!ei)
 		return NULL;
-
-	if (unlikely(percpu_init_rwsem(&ei->bdev.bd_block_size_semaphore))) {
-		kmem_cache_free(bdev_cachep, ei);
-		return NULL;
-	}
-
 	return &ei->vfs_inode;
 }
 
···
 {
 	struct inode *inode = container_of(head, struct inode, i_rcu);
 	struct bdev_inode *bdi = BDEV_I(inode);
-
-	percpu_free_rwsem(&bdi->bdev.bd_block_size_semaphore);
 
 	kmem_cache_free(bdev_cachep, bdi);
 }
···
 	return blkdev_ioctl(bdev, mode, cmd, arg);
 }
 
-ssize_t blkdev_aio_read(struct kiocb *iocb, const struct iovec *iov,
-			unsigned long nr_segs, loff_t pos)
-{
-	ssize_t ret;
-	struct block_device *bdev = I_BDEV(iocb->ki_filp->f_mapping->host);
-
-	percpu_down_read(&bdev->bd_block_size_semaphore);
-
-	ret = generic_file_aio_read(iocb, iov, nr_segs, pos);
-
-	percpu_up_read(&bdev->bd_block_size_semaphore);
-
-	return ret;
-}
-EXPORT_SYMBOL_GPL(blkdev_aio_read);
-
 /*
  * Write data to the block device.  Only intended for the block device itself
  * and the raw driver which basically is a fake block device.
···
 			 unsigned long nr_segs, loff_t pos)
 {
 	struct file *file = iocb->ki_filp;
-	struct block_device *bdev = I_BDEV(file->f_mapping->host);
 	struct blk_plug plug;
 	ssize_t ret;
 
 	BUG_ON(iocb->ki_pos != pos);
 
 	blk_start_plug(&plug);
-
-	percpu_down_read(&bdev->bd_block_size_semaphore);
-
 	ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);
 	if (ret > 0 || ret == -EIOCBQUEUED) {
 		ssize_t err;
···
 		if (err < 0 && ret > 0)
 			ret = err;
 	}
-
-	percpu_up_read(&bdev->bd_block_size_semaphore);
-
 	blk_finish_plug(&plug);
-
 	return ret;
 }
 EXPORT_SYMBOL_GPL(blkdev_aio_write);
-
-static int blkdev_mmap(struct file *file, struct vm_area_struct *vma)
-{
-	int ret;
-	struct block_device *bdev = I_BDEV(file->f_mapping->host);
-
-	percpu_down_read(&bdev->bd_block_size_semaphore);
-
-	ret = generic_file_mmap(file, vma);
-
-	percpu_up_read(&bdev->bd_block_size_semaphore);
-
-	return ret;
-}
-
-static ssize_t blkdev_splice_read(struct file *file, loff_t *ppos,
-				  struct pipe_inode_info *pipe, size_t len,
-				  unsigned int flags)
-{
-	ssize_t ret;
-	struct block_device *bdev = I_BDEV(file->f_mapping->host);
-
-	percpu_down_read(&bdev->bd_block_size_semaphore);
-
-	ret = generic_file_splice_read(file, ppos, pipe, len, flags);
-
-	percpu_up_read(&bdev->bd_block_size_semaphore);
-
-	return ret;
-}
-
-static ssize_t blkdev_splice_write(struct pipe_inode_info *pipe,
-				   struct file *file, loff_t *ppos, size_t len,
-				   unsigned int flags)
-{
-	ssize_t ret;
-	struct block_device *bdev = I_BDEV(file->f_mapping->host);
-
-	percpu_down_read(&bdev->bd_block_size_semaphore);
-
-	ret = generic_file_splice_write(pipe, file, ppos, len, flags);
-
-	percpu_up_read(&bdev->bd_block_size_semaphore);
-
-	return ret;
-}
-
 
 /*
  * Try to release a page associated with block device when the system
···
 	.llseek		= block_llseek,
 	.read		= do_sync_read,
 	.write		= do_sync_write,
-  	.aio_read	= blkdev_aio_read,
+	.aio_read	= generic_file_aio_read,
 	.aio_write	= blkdev_aio_write,
-	.mmap		= blkdev_mmap,
+	.mmap		= generic_file_mmap,
 	.fsync		= blkdev_fsync,
 	.unlocked_ioctl	= block_ioctl,
 #ifdef CONFIG_COMPAT
 	.compat_ioctl	= compat_blkdev_ioctl,
 #endif
-	.splice_read	= blkdev_splice_read,
-	.splice_write	= blkdev_splice_write,
+	.splice_read	= generic_file_splice_read,
+	.splice_write	= generic_file_splice_write,
 };
 
 int ioctl_by_bdev(struct block_device *bdev, unsigned cmd, unsigned long arg)

fs/buffer.c

···
 	attach_page_buffers(page, head);
 }
 
+static sector_t blkdev_max_block(struct block_device *bdev, unsigned int size)
+{
+	sector_t retval = ~((sector_t)0);
+	loff_t sz = i_size_read(bdev->bd_inode);
+
+	if (sz) {
+		unsigned int sizebits = blksize_bits(size);
+		retval = (sz >> sizebits);
+	}
+	return retval;
+}
+
 /*
  * Initialise the state of a blockdev page's buffers.
  */ 
···
 	struct buffer_head *head = page_buffers(page);
 	struct buffer_head *bh = head;
 	int uptodate = PageUptodate(page);
-	sector_t end_block = blkdev_max_block(I_BDEV(bdev->bd_inode));
+	sector_t end_block = blkdev_max_block(I_BDEV(bdev->bd_inode), size);
 
 	do {
 		if (!buffer_mapped(bh)) {
···
 EXPORT_SYMBOL(unmap_underlying_metadata);
 
 /*
+ * Size is a power-of-two in the range 512..PAGE_SIZE,
+ * and the case we care about most is PAGE_SIZE.
+ *
+ * So this *could* possibly be written with those
+ * constraints in mind (relevant mostly if some
+ * architecture has a slow bit-scan instruction)
+ */
+static inline int block_size_bits(unsigned int blocksize)
+{
+	return ilog2(blocksize);
+}
+
+static struct buffer_head *create_page_buffers(struct page *page, struct inode *inode, unsigned int b_state)
+{
+	BUG_ON(!PageLocked(page));
+
+	if (!page_has_buffers(page))
+		create_empty_buffers(page, 1 << ACCESS_ONCE(inode->i_blkbits), b_state);
+	return page_buffers(page);
+}
+
+/*
  * NOTE! All mapped/uptodate combinations are valid:
  *
  *	Mapped	Uptodate	Meaning
···
 	sector_t block;
 	sector_t last_block;
 	struct buffer_head *bh, *head;
-	const unsigned blocksize = 1 << inode->i_blkbits;
+	unsigned int blocksize, bbits;
 	int nr_underway = 0;
 	int write_op = (wbc->sync_mode == WB_SYNC_ALL ?
 			WRITE_SYNC : WRITE);
 
-	BUG_ON(!PageLocked(page));
-
-	last_block = (i_size_read(inode) - 1) >> inode->i_blkbits;
-
-	if (!page_has_buffers(page)) {
-		create_empty_buffers(page, blocksize,
+	head = create_page_buffers(page, inode,
 					(1 << BH_Dirty)|(1 << BH_Uptodate));
-	}
 
 	/*
 	 * Be very careful.  We have no exclusion from __set_page_dirty_buffers
···
 	 * handle that here by just cleaning them.
 	 */
 
-	block = (sector_t)page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
-	head = page_buffers(page);
 	bh = head;
+	blocksize = bh->b_size;
+	bbits = block_size_bits(blocksize);
+
+	block = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
+	last_block = (i_size_read(inode) - 1) >> bbits;
 
 	/*
 	 * Get all the dirty buffers mapped to disk addresses and
···
 	BUG_ON(to > PAGE_CACHE_SIZE);
 	BUG_ON(from > to);
 
-	blocksize = 1 << inode->i_blkbits;
-	if (!page_has_buffers(page))
-		create_empty_buffers(page, blocksize, 0);
-	head = page_buffers(page);
+	head = create_page_buffers(page, inode, 0);
+	blocksize = head->b_size;
+	bbits = block_size_bits(blocksize);
 
-	bbits = inode->i_blkbits;
 	block = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
 
 	for(bh = head, block_start = 0; bh != head || !block_start;
···
 	unsigned blocksize;
 	struct buffer_head *bh, *head;
 
-	blocksize = 1 << inode->i_blkbits;
+	bh = head = page_buffers(page);
+	blocksize = bh->b_size;
 
-	for(bh = head = page_buffers(page), block_start = 0;
-	    bh != head || !block_start;
-	    block_start=block_end, bh = bh->b_this_page) {
+	block_start = 0;
+	do {
 		block_end = block_start + blocksize;
 		if (block_end <= from || block_start >= to) {
 			if (!buffer_uptodate(bh))
···
 			mark_buffer_dirty(bh);
 		}
 		clear_buffer_new(bh);
-	}
+
+		block_start = block_end;
+		bh = bh->b_this_page;
+	} while (bh != head);
 
 	/*
 	 * If this is a partial write which happened to make all buffers
···
 int block_is_partially_uptodate(struct page *page, read_descriptor_t *desc,
 					unsigned long from)
 {
-	struct inode *inode = page->mapping->host;
 	unsigned block_start, block_end, blocksize;
 	unsigned to;
 	struct buffer_head *bh, *head;
···
 	if (!page_has_buffers(page))
 		return 0;
 
-	blocksize = 1 << inode->i_blkbits;
+	head = page_buffers(page);
+	blocksize = head->b_size;
 	to = min_t(unsigned, PAGE_CACHE_SIZE - from, desc->count);
 	to = from + to;
 	if (from < blocksize && to > PAGE_CACHE_SIZE - blocksize)
 		return 0;
 
-	head = page_buffers(page);
 	bh = head;
 	block_start = 0;
 	do {
···
 	struct inode *inode = page->mapping->host;
 	sector_t iblock, lblock;
 	struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
-	unsigned int blocksize;
+	unsigned int blocksize, bbits;
 	int nr, i;
 	int fully_mapped = 1;
 
-	BUG_ON(!PageLocked(page));
-	blocksize = 1 << inode->i_blkbits;
-	if (!page_has_buffers(page))
-		create_empty_buffers(page, blocksize, 0);
-	head = page_buffers(page);
+	head = create_page_buffers(page, inode, 0);
+	blocksize = head->b_size;
+	bbits = block_size_bits(blocksize);
 
-	iblock = (sector_t)page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
-	lblock = (i_size_read(inode)+blocksize-1) >> inode->i_blkbits;
+	iblock = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
+	lblock = (i_size_read(inode)+blocksize-1) >> bbits;
 	bh = head;
 	nr = 0;
 	i = 0;

fs/direct-io.c

···
 	sector_t fs_endblk;	/* Into file, in filesystem-sized blocks */
 	unsigned long fs_count;	/* Number of filesystem-sized blocks */
 	int create;
+	unsigned int i_blkbits = sdio->blkbits + sdio->blkfactor;
 
 	/*
 	 * If there was a memory error and we've overwritten all the
···
 		fs_count = fs_endblk - fs_startblk + 1;
 
 		map_bh->b_state = 0;
-		map_bh->b_size = fs_count << dio->inode->i_blkbits;
+		map_bh->b_size = fs_count << i_blkbits;
 
 		/*
 		 * For writes inside i_size on a DIO_SKIP_HOLES filesystem we
···
 	int seg;
 	size_t size;
 	unsigned long addr;
-	unsigned blkbits = inode->i_blkbits;
+	unsigned i_blkbits = ACCESS_ONCE(inode->i_blkbits);
+	unsigned blkbits = i_blkbits;
 	unsigned blocksize_mask = (1 << blkbits) - 1;
 	ssize_t retval = -EINVAL;
 	loff_t end = offset;
···
 	dio->inode = inode;
 	dio->rw = rw;
 	sdio.blkbits = blkbits;
-	sdio.blkfactor = inode->i_blkbits - blkbits;
+	sdio.blkfactor = i_blkbits - blkbits;
 	sdio.block_in_file = offset >> blkbits;
 
 	sdio.get_block = get_block;

include/linux/fs.h

···
 	int			bd_fsfreeze_count;
 	/* Mutex for freeze */
 	struct mutex		bd_fsfreeze_mutex;
-	/* A semaphore that prevents I/O while block size is being changed */
-	struct percpu_rw_semaphore	bd_block_size_semaphore;
 };
 
 /*
···
 extern struct block_device *bdget(dev_t);
 extern struct block_device *bdgrab(struct block_device *bdev);
 extern void bd_set_size(struct block_device *, loff_t size);
-extern sector_t blkdev_max_block(struct block_device *bdev);
 extern void bd_forget(struct inode *inode);
 extern void bdput(struct block_device *);
 extern void invalidate_bdev(struct block_device *);
···
 		unsigned long *nr_segs, size_t *count, int access_flags);
 
 /* fs/block_dev.c */
-extern ssize_t blkdev_aio_read(struct kiocb *iocb, const struct iovec *iov,
-			       unsigned long nr_segs, loff_t pos);
 extern ssize_t blkdev_aio_write(struct kiocb *iocb, const struct iovec *iov,
 				unsigned long nr_segs, loff_t pos);
 extern int blkdev_fsync(struct file *filp, loff_t start, loff_t end,