[PATCH] PM/hibernate: replace bdget call with bdcopy (simple atomic_inc of i_count)

[Alan Jenkins]

Create bdcopy().  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).

Signed-off-by: Alan Jenkins <alan-jenkins@xxxxxxxxxxxxxx>
CC: linux-fsdevel@xxxxxxxxxxxxxxx
---
 fs/block_dev.c     |    8 ++++++++
 include/linux/fs.h |    1 +
 mm/swapfile.c      |    4 ++--
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 3a6d4fb..0b04974 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -564,6 +564,14 @@ struct block_device *bdget(dev_t dev)
 
 EXPORT_SYMBOL(bdget);
 
+struct block_device *bdcopy(struct block_device *bdev)
+{
+	atomic_inc(&bdev->bd_inode->i_count);
+	return bdev;
+}
+
+EXPORT_SYMBOL(bdcopy);
+
 long nr_blockdev_pages(void)
 {
 	struct block_device *bdev;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 0872372..eeb1091 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 *bdcopy(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 d1ade1a..272ea8e 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 = bdcopy(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 = bdcopy(sis->bdev);
 
 				spin_unlock(&swap_lock);
 				bdput(bdev);
-- 
1.6.3.2



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