netdev - Aw: Re: stmmac ethernet in kernel 4.9-rc6: coalescing related pauses.

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Message-ID: <trinity-11729d3e-ae5e-4850-a1bf-b83a1d0a864c-1480687521037@3capp-gmx-bs55>
Date:   Fri, 2 Dec 2016 15:05:21 +0100
From:   "Lino Sanfilippo" <LinoSanfilippo@....de>
To:     "Pavel Machek" <pavel@....cz>
Cc:     "Giuseppe CAVALLARO" <peppe.cavallaro@...com>,
        alexandre.torgue@...com, "David Miller" <davem@...emloft.net>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Aw: Re: stmmac ethernet in kernel 4.9-rc6: coalescing related
 pauses.

Hi,

> 
> There's nothing that protect stmmac_poll() from running concurently
> with stmmac_dma_interrupt(), right?
> 

could it be that there is also another issue concerned locking?:
The tx completion handler takes the xmit_lock in case that the
netif_queue is stopped. This is AFAICS unnecessary, since both
xmit and completion handler are already synchronized by the private
tx lock. But it is IMHO also dangerous:

In the xmit handler we have the locking order
1. xmit_lock
2. private tx lock

while in the completion handler its the reverse:

1. private tx lock
2. xmit lock.

Do I miss something?

Regards,
Lino