linux-kernel - Re: [PATCH 9/9] u64_stat: Remove the obsolete fetch

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Date:   Mon, 22 Aug 2022 11:05:43 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>, netdev@...r.kernel.org
Subject: Re: [PATCH 9/9] u64_stat: Remove the obsolete fetch_irq() variants

On Mon, 22 Aug 2022 17:17:00 +0200 Sebastian Andrzej Siewior wrote:
> Using u64_stats_fetch_begin() is most likely wrong in networking because
> the stats are updated while packets are received which is either in IRQ
> or in BH (except maybe for the SPI/I2C ethernet driver). The _bh()
> version was replaced with _irq() for netpoll reasons.
> u64_stats_fetch_begin() does not disable any of those two (IRQ, BH) on
> 32bit-UP and does not use a seqcount so it is possible that an update
> happens during the read out of stats. Let me look…
> 	drivers/net/ethernet/cortina/gemini.c
> reads in net_device_ops::ndo_get_stats64(), updates in NAPI.
> 
> 	drivers/net/ethernet/huawei/hinic/hinic_rx.c
> reads in net_device_ops::ndo_get_stats64() and
> ethtool_ops::get_ethtool_stats(), updates in NAPI. Good.
> 
> So I guess these want be fixed properly instead of silently via the
> series?

Guess so, but it shouldn't be extra work if we're delaying the driver
conversion till 6.1?