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

Reported-by: Weijie Yang <[email protected]>
Signed-off-by: Krzysztof Kozlowski <[email protected]>
---
 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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