linux-kernel - [ 070/117] swap: dont do discard if no discard option added

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Date:	Mon, 28 May 2012 04:13:12 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Shaohua Li <shli@...nel.org>,
	Shaohua Li <shli@...ionio.com>,
	Holger Kiehl <Holger.Kiehl@....de>,
	Hugh Dickins <hughd@...gle.com>
Subject: [ 070/117] swap: dont do discard if no discard option added

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Shaohua Li <shli@...nel.org>

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@...ionio.com>
Reported-by: Holger Kiehl <Holger.Kiehl@....de>
Tested-by: Holger Kiehl <Holger.Kiehl@....de>
Cc: Hugh Dickins <hughd@...gle.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 mm/swapfile.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index b82c028..21b5694 100644
--- 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;
 	}
 


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