[PATCH] swap: Fix swap size in case of block devices

[Nitin Gupta <ngupta@vflare.org>]

During swapon, swap size is set to number of usable pages in the given
swap file/block device minus 1 (for header page). In case of block devices,
this size is incorrectly set as one page less than the actual due to an
off-by-one error. For regular files, this size is set correctly.

Signed-off-by: Nitin Gupta <ngupta@vflare.org>
---

 mm/swapfile.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 8ffdc0d..3d37b97 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1951,9 +1951,9 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	if (error)
 		goto bad_swap;

+	/* excluding header page */
 	nr_good_pages = swap_header->info.last_page -
-			swap_header->info.nr_badpages -
-			1 /* header page */;
+			swap_header->info.nr_badpages;

 	if (nr_good_pages) {
 		swap_map[0] = SWAP_MAP_BAD;

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