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

commit 052b1987faca3606109d88d96bce124851f7c4c2 upstream.

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 <shli@fusionio.com>
Reported-by: Holger Kiehl <Holger.Kiehl@dwd.de>
Tested-by: Holger Kiehl <Holger.Kiehl@dwd.de>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 2015a1e..d3955f2 100644 (file)
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2102,7 +2102,7 @@ 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;
        }