PM / Hibernate: Replace bdget call with simple atomic_inc of i_count

Create bdgrab().  This function copies an existing reference to a
block_device.  It is safe to call from any context.

Hibernation code wishes to copy a reference to the active swap device.
Right now it calls bdget() under a spinlock, but this is wrong because
bdget() can sleep.  It doesn't need a full bdget() because we already
hold a reference to active swap devices (and the spinlock protects
against swapoff).

Fixes http://bugzilla.kernel.org/show_bug.cgi?id=13827

Signed-off-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

3 files changed, 13 insertions, 2 deletions

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 3a6d4fb2a329..94dfda24c06e 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -564,6 +564,16 @@ struct block_device *bdget(dev_t dev)
 
 EXPORT_SYMBOL(bdget);
 
+/**
+ * bdgrab -- Grab a reference to an already referenced block device
+ * @bdev:       Block device to grab a reference to.
+ */
+struct block_device *bdgrab(struct block_device *bdev)
+{
+        atomic_inc(&bdev->bd_inode->i_count);
+        return bdev;
+}
+
 long nr_blockdev_pages(void)
 {
         struct block_device *bdev;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 0872372184fe..a36ffa5a77a4 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1946,6 +1946,7 @@ extern void putname(const char *name);
 extern int register_blkdev(unsigned int, const char *);
 extern void unregister_blkdev(unsigned int, const char *);
 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 void bd_forget(struct inode *inode);
 extern void bdput(struct block_device *);
diff --git a/mm/swapfile.c b/mm/swapfile.c
index d1ade1a48ee7..8ffdc0d23c53 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -753,7 +753,7 @@ int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
 
                 if (!bdev) {
                         if (bdev_p)
-                                *bdev_p = bdget(sis->bdev->bd_dev);
+                                *bdev_p = bdgrab(sis->bdev);
 
                         spin_unlock(&swap_lock);
                         return i;
@@ -765,7 +765,7 @@ int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
                                         struct swap_extent, list);
                         if (se->start_block == offset) {
                                 if (bdev_p)
-                                        *bdev_p = bdget(sis->bdev->bd_dev);
+                                        *bdev_p = bdgrab(sis->bdev);
 
                                 spin_unlock(&swap_lock);
                                 bdput(bdev);