Re: 2.6.23-rc6-mm1: IPC: sleeping function called ...

[Nadia Derbey]

Andrew Morton wrote:
> On Tue, 18 Sep 2007 13:17:28 +0400 Alexey Dobriyan <adobriyan@xxxxx> wrote:
>
>
> > I'm getting tons of this, and X fails to start
> >
> > CONFIG_SYSVIPC=y
> > CONFIG_SYSVIPC_SYSCTL=y
> > # CONFIG_PREEMPT_NONE is not set
> > # CONFIG_PREEMPT_VOLUNTARY is not set
> > CONFIG_PREEMPT=y
> > CONFIG_PREEMPT_BKL=y
> > CONFIG_DEBUG_PREEMPT=y
> >
> > BUG: sleeping function called from invalid context at kernel/rwsem.c:47
> > in_atomic():1, irqs_disabled():0
>
>
> OK, this fixes the locking here:
>
> --- a/ipc/util.c~ipc-integrate-ipc_checkid-into-ipc_lock-fix-2
> +++ a/ipc/util.c
> @@ -295,7 +295,6 @@ int ipc_addid(struct ipc_ids* ids, struc
>  
>  	spin_lock_init(&new->lock);
>  	new->deleted = 0;
> -	rcu_read_lock();
>  	spin_lock(&new->lock);
>  	return id;
>  }
> @@ -691,7 +690,7 @@ struct kern_ipc_perm *ipc_lock(struct ip
>  		rcu_read_unlock();
>  		return ERR_PTR(-EINVAL);
>  	}
> -
> +	rcu_read_unlock();
>  	return out;
>  }
>  


Well, reviewing the code I found another place where the 
rcu_read_unlock() was missing.
I'm so sorry for the inconvenience. It's true that I should have tested 
with CONFIG_PREEMPT=y :-(
Now, the ltp tests pass even with this option set...

In attachment you'll find a patch thhat
1) adds the missing rcu_read_unlock()
2) replaces Andrew's fix with a new one: the rcu_read_lock() is now 
taken in ipc_lock() / ipc_lock_by_ptr() and released in ipc_unlock(), 
exactly as it was done in the ref code.

Regards,
Nadia
This patch fixes the missing rcu_read_(un)lock in the ipc code

Signed-off-by: Nadia Derbey <Nadia.Derbey@xxxxxxxx>

---
 ipc/util.c |    3 ++-
 ipc/util.h |    4 +++-
 2 files changed, 5 insertions(+), 2 deletions(-)

Index: linux-2.6.23-rc6-mm1/ipc/util.c
===================================================================
--- linux-2.6.23-rc6-mm1.orig/ipc/util.c	2007-09-18 16:39:43.000000000 +0200
+++ linux-2.6.23-rc6-mm1/ipc/util.c	2007-09-18 16:40:53.000000000 +0200
@@ -295,6 +295,7 @@ int ipc_addid(struct ipc_ids* ids, struc
 
 	spin_lock_init(&new->lock);
 	new->deleted = 0;
+	rcu_read_lock();
 	spin_lock(&new->lock);
 	return id;
 }
@@ -690,7 +691,7 @@ struct kern_ipc_perm *ipc_lock(struct ip
 		rcu_read_unlock();
 		return ERR_PTR(-EINVAL);
 	}
-	rcu_read_unlock();
+
 	return out;
 }
 
Index: linux-2.6.23-rc6-mm1/ipc/util.h
===================================================================
--- linux-2.6.23-rc6-mm1.orig/ipc/util.h	2007-09-18 14:55:31.000000000 +0200
+++ linux-2.6.23-rc6-mm1/ipc/util.h	2007-09-18 16:41:37.000000000 +0200
@@ -141,12 +141,14 @@ static inline int ipc_checkid(struct ipc
 
 static inline void ipc_lock_by_ptr(struct kern_ipc_perm *perm)
 {
+	rcu_read_lock();
 	spin_lock(&perm->lock);
 }
 
 static inline void ipc_unlock(struct kern_ipc_perm *perm)
 {
 	spin_unlock(&perm->lock);
+	rcu_read_unlock();
 }
 
 static inline struct kern_ipc_perm *ipc_lock_check(struct ipc_ids *ids,
@@ -159,7 +161,7 @@ static inline struct kern_ipc_perm *ipc_
 		return out;
 
 	if (ipc_checkid(ids, out, id)) {
-		spin_unlock(&out->lock);
+		ipc_unlock(out);
 		return ERR_PTR(-EIDRM);
 	}