dax: fix lifetime of in-kernel dax mappings with dax_map_atomic()

The DAX implementation needs to protect new calls to ->direct_access()
and usage of its return value against the driver for the underlying
block device being disabled.  Use blk_queue_enter()/blk_queue_exit() to
hold off blk_cleanup_queue() from proceeding, or otherwise fail new
mapping requests if the request_queue is being torn down.

This also introduces blk_dax_ctl to simplify the interface from fs/dax.c
through dax_map_atomic() to bdev_direct_access().

[willy@linux.intel.com: fix read() of a hole]
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Cc: Jan Kara <jack@suse.com>
Cc: Jens Axboe <axboe@fb.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/block_dev.c

@@ -455,10 +455,7 @@ EXPORT_SYMBOL_GPL(bdev_write_page);
 /**
  * bdev_direct_access() - Get the address for directly-accessibly memory
  * @bdev: The device containing the memory
- * @sector: The offset within the device
- * @addr: Where to put the address of the memory
- * @pfn: The Page Frame Number for the memory
- * @size: The number of bytes requested
+ * @dax: control and output parameters for ->direct_access
  *
  * If a block device is made up of directly addressable memory, this function
  * will tell the caller the PFN and the address of the memory.  The address
@@ -469,10 +466,10 @@ EXPORT_SYMBOL_GPL(bdev_write_page);
  * Return: negative errno if an error occurs, otherwise the number of bytes
  * accessible at this address.
  */
-long bdev_direct_access(struct block_device *bdev, sector_t sector,
-			void __pmem **addr, unsigned long *pfn, long size)
+long bdev_direct_access(struct block_device *bdev, struct blk_dax_ctl *dax)
 {
-	long avail;
+	sector_t sector = dax->sector;
+	long avail, size = dax->size;
 	const struct block_device_operations *ops = bdev->bd_disk->fops;
 
 	/*
@@ -491,7 +488,7 @@ long bdev_direct_access(struct block_device *bdev, sector_t sector,
 	sector += get_start_sect(bdev);
 	if (sector % (PAGE_SIZE / 512))
 		return -EINVAL;
-	avail = ops->direct_access(bdev, sector, addr, pfn);
+	avail = ops->direct_access(bdev, sector, &dax->addr, &dax->pfn);
 	if (!avail)
 		return -ERANGE;
 	if (avail > 0 && avail & ~PAGE_MASK)

include/linux/blkdev.h

@@ -1617,6 +1617,20 @@ static inline bool integrity_req_gap_front_merge(struct request *req,
 
 #endif /* CONFIG_BLK_DEV_INTEGRITY */
 
+/**
+ * struct blk_dax_ctl - control and output parameters for ->direct_access
+ * @sector: (input) offset relative to a block_device
+ * @addr: (output) kernel virtual address for @sector populated by driver
+ * @pfn: (output) page frame number for @addr populated by driver
+ * @size: (input) number of bytes requested
+ */
+struct blk_dax_ctl {
+	sector_t sector;
+	void __pmem *addr;
+	long size;
+	unsigned long pfn;
+};
+
 struct block_device_operations {
 	int (*open) (struct block_device *, fmode_t);
 	void (*release) (struct gendisk *, fmode_t);
@@ -1643,8 +1657,7 @@ extern int __blkdev_driver_ioctl(struct block_device *, fmode_t, unsigned int,
 extern int bdev_read_page(struct block_device *, sector_t, struct page *);
 extern int bdev_write_page(struct block_device *, sector_t, struct page *,
 						struct writeback_control *);
-extern long bdev_direct_access(struct block_device *, sector_t,
-		void __pmem **addr, unsigned long *pfn, long size);
+extern long bdev_direct_access(struct block_device *, struct blk_dax_ctl *);
 #else /* CONFIG_BLOCK */
 
 struct block_device;