netdev - Re: [PATCH net] sky2: Do not deadlock on sky2_hw

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Message-Id: <20170525.134205.884395652948196578.davem@davemloft.net>
Date:   Thu, 25 May 2017 13:42:05 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     jemele@...il.com
Cc:     netdev@...r.kernel.org, jemele@...gle.com, mlindner@...vell.com,
        stephen@...workplumber.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] sky2: Do not deadlock on sky2_hw_down

From: Joshua Emele <jemele@...il.com>
Date: Wed, 24 May 2017 15:43:18 -0700

> From: Joshua Emele <jemele@...gle.com>
> 
> The sky2_hw_down uses sky2_tx_complete to free pending frames stuck in
> the HW queue. Because sky2_hw_down can be called from a process context,
> the call to u64_stats_update_begin can result in deadlock.
> 
> Because the statistics do not require update as part of the sky2_hw_down
> sequence, prevent the update to avoid the deadlock.

I disagree.  Taking the interface down should cause events in the
statistics to be lost.

You're going to have to find a way to fix this without eliding
the stats increments.

Thanks.