From: Shaohua Li <shli@kernel.org>
Date: Wed, 21 Mar 2012 23:34:17 +0000 (-0700)
Subject: swap: don't do discard if no discard option added
X-Git-Tag: v3.2.19~48
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=07fb30fa5b317e65a6953471886b7fd04e1acb51;p=thirdparty%2Fkernel%2Fstable.git

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 2015a1e42dc0f..d3955f2745e53 100644
--- 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;
 	}