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

3 files changed, 71 insertions, 190 deletions

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 1a1e5e3b1eaf..a1e09b4fe1ba 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -70,19 +70,6 @@ static void bdev_inode_switch_bdi(struct inode *inode,
         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)
 {
@@ -116,8 +103,6 @@ EXPORT_SYMBOL(invalidate_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;
@@ -126,19 +111,6 @@ int set_blocksize(struct block_device *bdev, int size)
         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);
@@ -146,9 +118,6 @@ int set_blocksize(struct block_device *bdev, int size)
                 bdev->bd_inode->i_blkbits = blksize_bits(size);
                 kill_bdev(bdev);
         }
-
-        percpu_up_write(&bdev->bd_block_size_semaphore);
-
         return 0;
 }
 
@@ -181,52 +150,12 @@ static int
 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;
-}
-
 static ssize_t
 blkdev_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
                         loff_t offset, unsigned long nr_segs)
@@ -235,7 +164,7 @@ blkdev_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
         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)
@@ -459,12 +388,6 @@ static struct inode *bdev_alloc_inode(struct super_block *sb)
         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;
 }
 
@@ -473,8 +396,6 @@ static void bdev_i_callback(struct rcu_head *head)
         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);
 }
 
@@ -1593,22 +1514,6 @@ static long block_ioctl(struct file *file, unsigned cmd, unsigned long arg)
         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.
@@ -1620,16 +1525,12 @@ ssize_t blkdev_aio_write(struct kiocb *iocb, const struct iovec *iov,
                          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;
@@ -1638,62 +1539,11 @@ ssize_t blkdev_aio_write(struct kiocb *iocb, const struct iovec *iov,
                 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
  * is under memory pressure.
@@ -1724,16 +1574,16 @@ const struct file_operations def_blk_fops = {
         .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)
diff --git a/fs/buffer.c b/fs/buffer.c
index b5f044283edb..3586fb05c8ce 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -911,6 +911,18 @@ link_dev_buffers(struct page *page, struct buffer_head *head)
         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.
  */ 
@@ -921,7 +933,7 @@ init_page_buffers(struct page *page, struct block_device *bdev,
         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)) {
@@ -1553,6 +1565,28 @@ void unmap_underlying_metadata(struct block_device *bdev, sector_t block)
 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
@@ -1589,19 +1623,13 @@ static int __block_write_full_page(struct inode *inode, struct page *page,
         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
@@ -1613,9 +1641,12 @@ static int __block_write_full_page(struct inode *inode, struct page *page,
          * 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
@@ -1806,12 +1837,10 @@ int __block_write_begin(struct page *page, loff_t pos, unsigned len,
         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;
@@ -1881,11 +1910,11 @@ static int __block_commit_write(struct inode *inode, struct page *page,
         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))
@@ -1895,7 +1924,10 @@ static int __block_commit_write(struct inode *inode, struct page *page,
                         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
@@ -2020,7 +2052,6 @@ EXPORT_SYMBOL(generic_write_end);
 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;
@@ -2029,13 +2060,13 @@ int block_is_partially_uptodate(struct page *page, read_descriptor_t *desc,
         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 {
@@ -2068,18 +2099,16 @@ int block_read_full_page(struct page *page, get_block_t *get_block)
         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;
diff --git a/fs/direct-io.c b/fs/direct-io.c
index f86c720dba0e..cf5b44b10c67 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -540,6 +540,7 @@ static int get_more_blocks(struct dio *dio, struct dio_submit *sdio,
         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
@@ -554,7 +555,7 @@ static int get_more_blocks(struct dio *dio, struct dio_submit *sdio,
                 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
@@ -1053,7 +1054,8 @@ do_blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
         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;
@@ -1149,7 +1151,7 @@ do_blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
         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;