swap: don't do discard if no discard option added

When swapon() was not passed the SWAP_FLAG_DISCARD option, sys_swapon()
will still perform a discard operation.  This can cause problems if
discard is slow or buggy.

Reverse the order of the check so that a discard operation is performed
only if the sys_swapon() caller is attempting to enable discard.

Signed-off-by: Shaohua Li <[email protected]>
Reported-by: Holger Kiehl <[email protected]>
Tested-by: Holger Kiehl <[email protected]>
Cc: Hugh Dickins <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/mm/swapfile.c b/mm/swapfile.c
index b82c028cfcc6fd8f1142dab3eaf92bd52b7e38e8..21b56945c5d22e81b756381481e18937e2ce3269 100644 (file)
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2103,7 +2103,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
                        p->flags |= SWP_SOLIDSTATE;
                        p->cluster_next = 1 + (random32() % p->highest_bit);
                }
-               if (discard_swap(p) == 0 && (swap_flags & SWAP_FLAG_DISCARD))
+               if ((swap_flags & SWAP_FLAG_DISCARD) && discard_swap(p) == 0)
                        p->flags |= SWP_DISCARDABLE;
        }