[PATCH next/mmotm] swap: add per-partition lock for swapfile fix

[Hugh Dickins]

I had all cpus spinning in swap_info_get(), for the lock on an area
being swapped off: probably because get_swap_page() forgot to unlock.

Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
---

 mm/swapfile.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

--- mmotm.orig/mm/swapfile.c	2013-01-23 17:55:39.132447115 -0800
+++ mmotm/mm/swapfile.c	2013-01-27 10:41:45.000000000 -0800
@@ -470,10 +470,9 @@ swp_entry_t get_swap_page(void)
 		spin_unlock(&swap_lock);
 		/* This is called for allocating swap entry for cache */
 		offset = scan_swap_map(si, SWAP_HAS_CACHE);
-		if (offset) {
-			spin_unlock(&si->lock);
+		spin_unlock(&si->lock);
+		if (offset)
 			return swp_entry(type, offset);
-		}
 		spin_lock(&swap_lock);
 		next = swap_list.next;
 	}
--
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