netdev - Re: [PATCH net 1/6] sctp: remove the unnecessary state check in sctp_outq

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Message-ID: <20160913115722.GA4501@hmsreliant.think-freely.org>
Date:   Tue, 13 Sep 2016 07:57:22 -0400
From:   Neil Horman <nhorman@...driver.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
        davem <davem@...emloft.net>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Vlad Yasevich <vyasevich@...il.com>, daniel@...earbox.net
Subject: Re: [PATCH net 1/6] sctp: remove the unnecessary state check in
 sctp_outq_tail

On Sat, Sep 10, 2016 at 12:03:53AM +0800, Xin Long wrote:
> > I don't know, I still don't feel safe about it.  I agree the socket lock keeps
> > the state from changing during a single transmission, which makes the use case
> > you are focused on correct.
> ok, :-)
> 
> >
> > That said, have you considered the retransmit case?  That is to say, if you
> > queue and flush the outq, and some packets fail delivery, and in the time
> > between the intial send and the expiration of the RTX timer (during which the
> > socket lock will have been released), an event may occur which changes the
> > transport state, which will then be ignored with your patch.
> Sorry, I'm not sure if I got it.
> 
> You mean "during which changes q->asoc->state", right ?
> 
> This patch removes the check of q->asoc->state in sctp_outq_tail().
> 
> sctp_outq_tail() is called for data only in:
> sctp_primitive_SEND -> sctp_do_sm -> sctp_cmd_send_msg ->
> sctp_cmd_interpreter -> sctp_cmd_send_msg() -> sctp_outq_tail()
> 
> before calling sctp_primitive_SEND, hold sock lock first.
> then sctp_primitive_SEND choose FUNC according:
> 
> #define TYPE_SCTP_PRIMITIVE_SEND  {
> ....
> 
> if asoc->state is unavailable, FUNC can't be sctp_cmd_send_msg,
> but sctp_sf_error_closed/sctp_sf_error_shutdown,  sctp_outq_tail
> can't be called, either.
> I mean sctp_primitive_SEND do the same check for asoc->state
> already actually.
> 
> so the code in sctp_outq_tail is redundant actually.
> 
> 
> 
> 
> >
> > Neil
> >
> 

Ok, you've convinced me, thanks for taking the time to go through it

Acked-by: Neil Horman <nhorman@...driver.com>