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

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Message-ID: <46EFA8DC.2020909@bull.net>
Date:	Tue, 18 Sep 2007 12:30:52 +0200
From:	Nadia Derbey <Nadia.Derbey@...l.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Alexey Dobriyan <adobriyan@...ru>, linux-kernel@...r.kernel.org
Subject: Re: 2.6.23-rc6-mm1: IPC: sleeping function called ...

Andrew Morton wrote:
> On Tue, 18 Sep 2007 13:17:28 +0400 Alexey Dobriyan <adobriyan@...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
>>no locks held by X/5879.
>> [<c012bcb1>] down_write+0x15/0x50
>> [<c01b53af>] do_shmat+0x235/0x3a0
>> [<c0106be2>] sys_ipc+0x146/0x263
>> [<c0102892>] sysenter_past_esp+0xa7/0xb5
>> [<c0102856>] sysenter_past_esp+0x6b/0xb5
>> =======================
> 
> 
> Here's a bug:
> 
> --- a/ipc/util.c~ipc-integrate-ipc_checkid-into-ipc_lock-fix-2
> +++ a/ipc/util.c
> @@ -691,7 +691,7 @@ struct kern_ipc_perm *ipc_lock(struct ip
>  		rcu_read_unlock();
>  		return ERR_PTR(-EINVAL);
>  	}
> -
> +	rcu_read_unlock();
>  	return out;
>  }
>  

Andrew,

Actually the rcu_read_lock is released in ipc_unlock(). So I think we 
shouldn't add an rcu_read_unlock() before leaving ipc_lock().
This is a part that has not changed since the ref code.

I'm looking also on my side.

Regards,
Nadia

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