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

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Date:	Thu, 20 Sep 2007 15:26:28 +0200
From:	Jarek Poplawski <jarkao2@...pl>
To:	Nadia Derbey <Nadia.Derbey@...l.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Alexey Dobriyan <adobriyan@...ru>, linux-kernel@...r.kernel.org
Subject: Re: 2.6.23-rc6-mm1: IPC: sleeping function called ...

On Thu, Sep 20, 2007 at 03:08:42PM +0200, Nadia Derbey wrote:
...
> So, here is the ipc_lock_by_ptr() status:
> 1) do_msgsnd(), semctl_main(GETALL), semctl_main(SETALL) and find_undo() 
> call it inside a refcounting.
>   ==> no rcu read section needed.
> 
> 2) *_exit_ns(), ipc_findkey() and sysvipc_find_ipc() call it under the 
> ipc_ids mutex lock.
>   ==> no rcu read section needed.
> 
> 3) do_msgrcv() is the only path where ipc_lock_by_ptr() is not called 
> under refcounting
>   ==> rcu read section + some more checks needed once the spnlock is
>       taken.
> 
> So I completely agree with you: we might remove the rcu_read_lock() from 
> the ipc_lock_by_ptr() and explicitley  call it when needed (actually, it 
> is already explicitly called in do_msgrcv()).

Impossible!

I've to look at this once more in the evening (and try to recall
what I've seen yesterday and forgotten today...).

Cheers,
Jarek P.
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