fuse: use kvmalloc to allocate array of pipe_buffer structs.

The amount of pipe->buffers is basically controlled by userspace by
fcntl(... F_SETPIPE_SZ ...) so it could be large. High order allocations
could be slow (if memory is heavily fragmented) or may fail if the order
is larger than PAGE_ALLOC_COSTLY_ORDER.

Since the 'bufs' doesn't need to be physically contiguous, use
the kvmalloc_array() to allocate memory. If high order
page isn't available, the kvamalloc*() will fallback to 0-order.
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/dev.c

@@ -1373,8 +1373,8 @@ static ssize_t fuse_dev_splice_read(struct file *in, loff_t *ppos,
 	if (!fud)
 		return -EPERM;
 
-	bufs = kmalloc_array(pipe->buffers, sizeof(struct pipe_buffer),
-			     GFP_KERNEL);
+	bufs = kvmalloc_array(pipe->buffers, sizeof(struct pipe_buffer),
+			      GFP_KERNEL);
 	if (!bufs)
 		return -ENOMEM;
 
@@ -1407,7 +1407,7 @@ static ssize_t fuse_dev_splice_read(struct file *in, loff_t *ppos,
 	for (; page_nr < cs.nr_segs; page_nr++)
 		put_page(bufs[page_nr].page);
 
-	kfree(bufs);
+	kvfree(bufs);
 	return ret;
 }
 
@@ -1957,8 +1957,8 @@ static ssize_t fuse_dev_splice_write(struct pipe_inode_info *pipe,
 
 	pipe_lock(pipe);
 
-	bufs = kmalloc_array(pipe->buffers, sizeof(struct pipe_buffer),
-			     GFP_KERNEL);
+	bufs = kvmalloc_array(pipe->buffers, sizeof(struct pipe_buffer),
+			      GFP_KERNEL);
 	if (!bufs) {
 		pipe_unlock(pipe);
 		return -ENOMEM;
@@ -2017,7 +2017,7 @@ static ssize_t fuse_dev_splice_write(struct pipe_inode_info *pipe,
 		pipe_buf_release(pipe, &bufs[idx]);
 
 out:
-	kfree(bufs);
+	kvfree(bufs);
 	return ret;
 }