[PATCH 2/2] arch/sh/mm: Eliminate a double lock

[PATCH 2/2] arch/sh/mm: Eliminate a double lock

[Julia Lawall]

From: Julia Lawall <julia@diku.dk>

The function begins and ends with a read_lock.  The latter is changed to a
read_unlock.

A simplified version of the semantic match that finds this problem is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
@locked@
expression E1;
position p;
@@

read_lock(E1@p,...);

@r exists@
expression x <= locked.E1;
expression locked.E1;
expression E2;
identifier lock;
position locked.p,p1,p2;
@@

*lock@p1 (E1@p,...);
... when != E1
    when != \(x = E2\|&x\)
*lock@p2 (E1,...);
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>

---
Not tested

 arch/sh/mm/pmb.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/sh/mm/pmb.c b/arch/sh/mm/pmb.c
index 18623ba..6379091 100644
--- a/arch/sh/mm/pmb.c
+++ b/arch/sh/mm/pmb.c
@@ -770,7 +770,7 @@ static void __init pmb_resize(void)
 		spin_unlock_irqrestore(&pmbe->lock, flags);
 	}
 
-	read_lock(&pmb_rwlock);
+	read_unlock(&pmb_rwlock);
 }
 #endif
 

Re: [PATCH 2/2] arch/sh/mm: Eliminate a double lock

[Matt Fleming]

On Sun, 20 Jun 2010 13:24:54 +0200 (CEST), Julia Lawall <julia@diku.dk> wrote:
> From: Julia Lawall <julia@diku.dk>
> 
> The function begins and ends with a read_lock.  The latter is changed to a
> read_unlock.

I think we've been quite lucky here so far, in that no one takes a
write_lock after we've double-read-locked pmb_rwlock.

Acked-by: Matt Fleming <matt@console-pimps.org>

Re: [PATCH 2/2] arch/sh/mm: Eliminate a double lock

[Paul Mundt]

On Sun, Jun 20, 2010 at 01:24:54PM +0200, Julia Lawall wrote:
> From: Julia Lawall <julia@diku.dk>
> 
> The function begins and ends with a read_lock.  The latter is changed to a
> read_unlock.
> 
Indeed, good catch. Applied, thanks.