Andrew Morton wrote:
> On Tue, 18 Sep 2007 13:17:28 +0400 Alexey Dobriyan <adobriyan@sw.ru> 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