netdev - Re: [PATCH net] sctp: Remove outqueue empty state

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Date:	Thu, 2 Jan 2014 15:40:56 -0500
From:	Neil Horman <nhorman@...driver.com>
To:	Vlad Yasevich <vyasevich@...il.com>
Cc:	netdev@...r.kernel.org, jhs@...atatu.com
Subject: Re: [PATCH net] sctp: Remove outqueue empty state

On Thu, Jan 02, 2014 at 02:39:44PM -0500, Vlad Yasevich wrote:
> The SCTP outqueue structure maintains a data chunks
> that are pending transmission, the list of chunks that
> are pending a retransmission and a length of data in
> flight.  It also tries to keep the emtpy state so that
> it can performe shutdown sequence or notify user.
> 
> The problem is that the empy state is inconsistently
> tracked.  It is possible to completely drain the queue
> without sending anything when using PR-SCTP.  In this
> case, the empty state will not be correctly state as
> report by Jamal Hadi Salim <jhs@...atatu.com>.  This
> can cause an association to be perminantly stuck in the
> SHUTDOWN_PENDING state.
> 
> Additionally, SCTP is incredibly inefficient when setting
> the empty state.  Even though all the data is availaible
> in the outqueue structure, we ignore it and walk a list
> of trasnports.
> 
> In the end, we can completely remove the extra empty
> state and figure out if the queue is empty by looking
> at 3 things:  length of pending data, length of in-flight
> data, and exisiting of retransmit data.  All of these
> are already in the strucutre.
> 
> Reported-by: Jamal Hadi Salim <jhs@...atatu.com>
> Signed-off-by: Vlad Yasevich <vyasevich@...il.com>

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

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