linux-kernel - [PATCH -mm -next] ipc,sem: fix lockdep false positive

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Date:	Mon, 25 Mar 2013 16:38:44 -0400
From:	Rik van Riel <riel@...riel.com>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	torvalds@...ux-foundation.org, davidlohr.bueso@...com,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	hhuang@...hat.com, jason.low2@...com, walken@...gle.com,
	lwoodman@...hat.com, chegu_vinod@...com,
	Dave Jones <davej@...hat.com>, benisty.e@...il.com
Subject: [PATCH -mm -next] ipc,sem: fix lockdep false positive

On Mon, 25 Mar 2013 16:21:22 -0400
Sasha Levin <sasha.levin@...cle.com> wrote:

> On 03/20/2013 03:55 PM, Rik van Riel wrote:
> > Include lkml in the CC: this time... *sigh*
> > ---8<---
> > 
> > This series makes the sysv semaphore code more scalable,
> > by reducing the time the semaphore lock is held, and making
> > the locking more scalable for semaphore arrays with multiple
> > semaphores.
> 
> Hi Rik,
> 
> I'm getting the following false positives from lockdep:

Does this patch fix it?

Andrew, this looks like another one for the queue...
---8<---
Subject: [PATCH -mm -next] ipc,sem: fix lockdep false positive

When locking all the semaphores inside a sem_array, the kernel ends up
locking a large number of locks with identical lockdep status. This
trips up lockdep.  Annotate the code to prevent such warnings.

Signed-off-by: Rik van Riel <riel@...hat.com>
---
 ipc/sem.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/ipc/sem.c b/ipc/sem.c
index 450248e..f46441a 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -357,7 +357,7 @@ static inline int sem_lock(struct sem_array *sma, struct sembuf *sops,
 		spin_lock(&sma->sem_perm.lock);
 		for (i = 0; i < sma->sem_nsems; i++) {
 			struct sem *sem = sma->sem_base + i;
-			spin_lock(&sem->lock);
+			spin_lock_nested(&sem->lock, SINGLE_DEPTH_NESTING);
 		}
 		locknum = -1;
 	}
@@ -558,7 +558,7 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params)
 	for (i = 0; i < nsems; i++) {
 		INIT_LIST_HEAD(&sma->sem_base[i].sem_pending);
 		spin_lock_init(&sma->sem_base[i].lock);
-		spin_lock(&sma->sem_base[i].lock);
+		spin_lock_nested(&sma->sem_base[i].lock, SINGLE_DEPTH_NESTING);
 	}
 
 	sma->complex_count = 0;

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