netdev - Re: [PATCH v4] PPTP: PPP over IPv4 (Point-to-Point Tunneling Protocol)

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Date:	Wed, 18 Aug 2010 17:16:09 +0400
From:	Dmitry Kozlov <xeb@...l.ru>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH v4] PPTP: PPP over IPv4 (Point-to-Point Tunneling Protocol)

> Hmm. You left a synchronize_rcu() call in add_chan() but this is not
> necessary. Please remove it or explain why you think it is needed.
> 
> synchronize_rcu(); in del_chan() is now fine, thanks.
> 
> 
> You use a mutex for gre_proto_lock, but you dont need a mutex, please
> use a spinlock like I suggested. I would have said 'use a mutex' if if
> was needed, you can trust me.

ok

> A mutex is needed if you can sleep while holding the lock, this is not
> the case here. A spinlock is faster and reduces to no-op on !SMP

then i have to replace mutex on spinlock in pptp module too ?

> Also, please remove the synchronize_rcu() call from gre_add_protocol() :
> It is not needed at all, like in add_chan().
> 
> (You dont have to wait for a RCU grace period when adding something,
> only when removing from a data structure)

ok, seems like i don't fully understand rcu mechanism...

Thanks for reply.

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