netdev - Re: [PATCH net] net: dsa: sja1105: Fix sleeping while atomic in .port_hwtstamp

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Message-Id: <20190930.172027.1837315999928472989.davem@davemloft.net>
Date:   Mon, 30 Sep 2019 17:20:27 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     olteanv@...il.com
Cc:     richardcochran@...il.com, andrew@...n.ch, f.fainelli@...il.com,
        vivien.didelot@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH net] net: dsa: sja1105: Fix sleeping while atomic in
 .port_hwtstamp_set

From: Vladimir Oltean <olteanv@...il.com>
Date: Sun, 29 Sep 2019 01:07:45 +0300

> Currently this stack trace can be seen with CONFIG_DEBUG_ATOMIC_SLEEP=y:
 ...
> Enabling RX timestamping will logically disturb the fastpath (processing
> of meta frames). Replace bool hwts_rx_en with a bit that is checked
> atomically from the fastpath and temporarily unset from the sleepable
> context during a change of the RX timestamping process (a destructive
> operation anyways, requires switch reset).
> If found unset, the fastpath will just drop any received meta frame and
> not take the meta_lock at all.
> 
> Fixes: a602afd200f5 ("net: dsa: sja1105: Expose PTP timestamping ioctls to userspace")
> Signed-off-by: Vladimir Oltean <olteanv@...il.com>

Well, two things:

1) Even assuming #2 wasn't true, you're adding the missing initialization
   of meta_lock and that would need to be mentioned in the commit message.

2) After these changes meta_lock is no longer used so it should be removed.