netdev - Re: [PATCH net] mlxsw: spectrum_ptp: Keep unmatched entries in a linked list

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Message-Id: <20190811.213603.1213098548868873560.davem@davemloft.net>
Date:   Sun, 11 Aug 2019 21:36:03 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     idosch@...sch.org
Cc:     netdev@...r.kernel.org, jiri@...lanox.com, petrm@...lanox.com,
        richardcochran@...il.com, mlxsw@...lanox.com, idosch@...lanox.com
Subject: Re: [PATCH net] mlxsw: spectrum_ptp: Keep unmatched entries in a
 linked list

From: Ido Schimmel <idosch@...sch.org>
Date: Sun, 11 Aug 2019 10:48:37 +0300

> From: Petr Machata <petrm@...lanox.com>
> 
> To identify timestamps for matching with their packets, Spectrum-1 uses a
> five-tuple of (port, direction, domain number, message type, sequence ID).
> If there are several clients from the same domain behind a single port
> sending Delay_Req's, the only thing differentiating these packets, as far
> as Spectrum-1 is concerned, is the sequence ID. Should sequence IDs between
> individual clients be similar, conflicts may arise. That is not a problem
> to hardware, which will simply deliver timestamps on a first comes, first
> served basis.
> 
> However the driver uses a simple hash table to store the unmatched pieces.
> When a new conflicting piece arrives, it pushes out the previously stored
> one, which if it is a packet, is delivered without timestamp. Later on as
> the corresponding timestamps arrive, the first one is mismatched to the
> second packet, and the second one is never matched and eventually is GCd.
> 
> To correct this issue, instead of using a simple rhashtable, use rhltable
> to keep the unmatched entries.
> 
> Previously, a found unmatched entry would always be removed from the hash
> table. That is not the case anymore--an incompatible entry is left in the
> hash table. Therefore removal from the hash table cannot be used to confirm
> the validity of the looked-up pointer, instead the lookup would simply need
> to be redone. Therefore move it inside the critical section. This
> simplifies a lot of the code.
> 
> Fixes: 8748642751ed ("mlxsw: spectrum: PTP: Support SIOCGHWTSTAMP, SIOCSHWTSTAMP ioctls")
> Reported-by: Alex Veber <alexve@...lanox.com>
> Signed-off-by: Petr Machata <petrm@...lanox.com>
> Signed-off-by: Ido Schimmel <idosch@...lanox.com>

Applied.