[PATCH] hibernate: unlock swap bdev for writing when uswsusp is active

["Darrick J. Wong" <darrick.wong@xxxxxxxxxx>]

From: Darrick J. Wong <darrick.wong@xxxxxxxxxx>

It turns out that there /is/ one use case for programs being able to
write to swap devices, and that is the userspace hibernation code.  The
uswsusp ioctls allow userspace to lease parts of swap devices, so turn
S_SWAPFILE off when invoking suspend.

Fixes: 1638045c3677 ("mm: set S_SWAPFILE on blockdev swap devices")
Reported-by: Domenico Andreoli <domenico.andreoli@xxxxxxxxx>
Reported-by: Marian Klein <mkleinsoft@xxxxxxxxx>
Tested-by: Marian Klein <mkleinsoft@xxxxxxxxx>
Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
---
 include/linux/swap.h |    1 +
 kernel/power/user.c  |   11 ++++++++++-
 mm/swapfile.c        |   26 ++++++++++++++++++++++++++
 3 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 1e99f7ac1d7e..add93e205850 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -458,6 +458,7 @@ extern void swap_free(swp_entry_t);
 extern void swapcache_free_entries(swp_entry_t *entries, int n);
 extern int free_swap_and_cache(swp_entry_t);
 extern int swap_type_of(dev_t, sector_t, struct block_device **);
+extern void swap_relockall(void);
 extern unsigned int count_swap_pages(int, int);
 extern sector_t map_swap_page(struct page *, struct block_device **);
 extern sector_t swapdev_block(int, pgoff_t);
diff --git a/kernel/power/user.c b/kernel/power/user.c
index 77438954cc2b..b11f7037ce5e 100644
--- a/kernel/power/user.c
+++ b/kernel/power/user.c
@@ -271,6 +271,8 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
 			break;
 		}
 		error = hibernation_restore(data->platform_support);
+		if (!error)
+			swap_relockall();
 		break;
 
 	case SNAPSHOT_FREE:
@@ -372,10 +374,17 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
 			 */
 			swdev = new_decode_dev(swap_area.dev);
 			if (swdev) {
+				struct block_device *bd;
+
 				offset = swap_area.offset;
-				data->swap = swap_type_of(swdev, offset, NULL);
+				data->swap = swap_type_of(swdev, offset, &bd);
 				if (data->swap < 0)
 					error = -ENODEV;
+
+				inode_lock(bd->bd_inode);
+				bd->bd_inode->i_flags &= ~S_SWAPFILE;
+				inode_unlock(bd->bd_inode);
+				bdput(bd);
 			} else {
 				data->swap = -1;
 				error = -EINVAL;
diff --git a/mm/swapfile.c b/mm/swapfile.c
index b2a2e45c9a36..439bfb7263d3 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1799,6 +1799,32 @@ int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
 	return -ENODEV;
 }
 
+/* Re-lock swap devices after resuming from userspace suspend. */
+void swap_relockall(void)
+{
+	int type;
+
+	spin_lock(&swap_lock);
+	for (type = 0; type < nr_swapfiles; type++) {
+		struct swap_info_struct *sis = swap_info[type];
+		struct block_device *bdev = bdgrab(sis->bdev);
+
+		/*
+		 * uswsusp only knows how to suspend to block devices, so we
+		 * can skip swap files.
+		 */
+		if (!(sis->flags & SWP_WRITEOK) ||
+		    !(sis->flags & SWP_BLKDEV))
+			continue;
+
+		inode_lock(bdev->bd_inode);
+		bdev->bd_inode->i_flags |= S_SWAPFILE;
+		inode_unlock(bdev->bd_inode);
+		bdput(bdev);
+	}
+	spin_unlock(&swap_lock);
+}
+
 /*
  * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev
  * corresponding to given index in swap_info (swap type).