[dm-devel] [PATCH] percpu-rw-semaphore: lock splice methods

[Mikulas Patocka]

Hi Jens

I actually forgot to lock functions generic_file_splice_read and 
generic_file_splice_write when submitting the commit 
b87570f5d349661814b262dd5fc40787700f80d6. They must be locked too.

Please apply this.

Mikulas

---

blockdev: use rwlock for splice

A rwlock that prevents changing block size while IO is being submitted
needs to be taken around generic_file_splice_read and
generic_file_splice_write functions. These functions manipulate the page
cache directly so block size must not change under them.

Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>

---
 fs/block_dev.c |   37 +++++++++++++++++++++++++++++++++++--
 1 file changed, 35 insertions(+), 2 deletions(-)

Index: linux-2.6-copy/fs/block_dev.c
===================================================================
--- linux-2.6-copy.orig/fs/block_dev.c	2012-10-04 02:26:01.000000000 +0200
+++ linux-2.6-copy/fs/block_dev.c	2012-10-04 02:30:37.000000000 +0200
@@ -1662,6 +1662,39 @@ static int blkdev_mmap(struct file *file
 	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.
@@ -1700,8 +1733,8 @@ const struct file_operations def_blk_fop
 #ifdef CONFIG_COMPAT
 	.compat_ioctl	= compat_blkdev_ioctl,
 #endif
-	.splice_read	= generic_file_splice_read,
-	.splice_write	= generic_file_splice_write,
+	.splice_read	= blkdev_splice_read,
+	.splice_write	= blkdev_splice_write,
 };
 
 int ioctl_by_bdev(struct block_device *bdev, unsigned cmd, unsigned long arg)