[PATCH] swap: fix set_blocksize race during swapon/swapoff

[Krzysztof Kozlowski <k.kozlowski@samsung.com>]

Swapoff used old_block_size from swap_info which could be overwritten by
concurrent swapon.

Reported-by: Weijie Yang <weijie.yang.kh@gmail.com>
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
---
 mm/swapfile.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 3963fc2..de7c904 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1824,6 +1824,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 	struct filename *pathname;
 	int i, type, prev;
 	int err;
+	unsigned int old_block_size;
 
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
@@ -1914,6 +1915,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 	}
 
 	swap_file = p->swap_file;
+	old_block_size = p->old_block_size;
 	p->swap_file = NULL;
 	p->max = 0;
 	swap_map = p->swap_map;
@@ -1938,7 +1940,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 	inode = mapping->host;
 	if (S_ISBLK(inode->i_mode)) {
 		struct block_device *bdev = I_BDEV(inode);
-		set_blocksize(bdev, p->old_block_size);
+		set_blocksize(bdev, old_block_size);
 		blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
 	} else {
 		mutex_lock(&inode->i_mutex);
-- 
1.7.9.5

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