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([2620:15c:2c1:200:55c7:81e6:c7d8:94b]) by smtp.gmail.com with ESMTPSA id w6sm10459081pfq.99.2020.01.21.15.52.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Jan 2020 15:52:59 -0800 (PST) Subject: Re: [PATCH net v2 01/12] net/sonic: Add mutual exclusion for accessing shared state To: Finn Thain Cc: "David S. Miller" , Thomas Bogendoerfer , Chris Zankel , Laurent Vivier , Geert Uytterhoeven , netdev@vger.kernel.org, linux-kernel@vger.kernel.org References: <0113c00f-3f77-8324-95a8-31dd6f64fa6a@gmail.com> From: Eric Dumazet Message-ID: <1b8d9cbe-94cf-2eb6-de44-2a2f9cb0a084@gmail.com> Date: Tue, 21 Jan 2020 15:52:58 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/21/20 3:33 PM, Finn Thain wrote: > On Tue, 21 Jan 2020, Eric Dumazet wrote: > >> On 1/21/20 1:22 PM, Finn Thain wrote: >>> The netif_stop_queue() call in sonic_send_packet() races with the >>> netif_wake_queue() call in sonic_interrupt(). This causes issues >>> like "NETDEV WATCHDOG: eth0 (macsonic): transmit queue 0 timed out". >>> Fix this by disabling interrupts when accessing tx_skb[] and next_tx. >>> Update a comment to clarify the synchronization properties. >>> >>> Fixes: efcce839360f ("[PATCH] macsonic/jazzsonic network drivers update") >>> Tested-by: Stan Johnson >>> Signed-off-by: Finn Thain >> >>> @@ -284,9 +287,16 @@ static irqreturn_t sonic_interrupt(int irq, void *dev_id) >>> struct net_device *dev = dev_id; >>> struct sonic_local *lp = netdev_priv(dev); >>> int status; >>> + unsigned long flags; >>> + >>> + spin_lock_irqsave(&lp->lock, flags); >> >> >> This is a hard irq handler, no need to block hard irqs. >> >> spin_lock() here is enough. >> > > Well, yes, assuming we're dealing with SMP [1]. Probably just disabling > pre-emption is all that will ever be needed. > > Anyway, the real problem solved by disabling irqs is that macsonic must > avoid re-entrance of sonic_interrupt(). [2] > > [1] > https://lore.kernel.org/netdev/alpine.LNX.2.21.1.2001211026190.8@nippy.intranet/T/#m0523c8b2a26a410ed56889d9230c37ba1160d40a > > [2] > https://lore.kernel.org/netdev/alpine.LNX.2.21.1.2001211026190.8@nippy.intranet/T/#m1c8ca580d2b45e61a628d17839978d0bd5aaf061 > Oh well... I would rather keep the m68k specific wrapper... Please add a fat comment of why spin_lock_irqsave() is used, to avoid a future 'cleanup', since average network developer wont be aware of m68k oddities.