netdev - Re: [net,PATCH v3] net: ks8851: Queue RX packets in IRQ handler instead of disabling BHs

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Message-ID: <CANn89iJvQnjSm0wCQVyX+Q3VKSEHB1c=RVr11dSLoRUMPG-BzA@mail.gmail.com>
Date: Fri, 3 May 2024 09:08:15 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Marek Vasut <marex@...x.de>
Cc: netdev@...r.kernel.org, Ronald Wahl <ronald.wahl@...itan.com>, 
	"David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Simon Horman <horms@...nel.org>
Subject: Re: [net,PATCH v3] net: ks8851: Queue RX packets in IRQ handler
 instead of disabling BHs

On Thu, May 2, 2024 at 8:34 PM Marek Vasut <marex@...x.de> wrote:
>
> Currently the driver uses local_bh_disable()/local_bh_enable() in its
> IRQ handler to avoid triggering net_rx_action() softirq on exit from
> netif_rx(). The net_rx_action() could trigger this driver .start_xmit
> callback, which is protected by the same lock as the IRQ handler, so
> calling the .start_xmit from netif_rx() from the IRQ handler critical
> section protected by the lock could lead to an attempt to claim the
> already claimed lock, and a hang.
>
> The local_bh_disable()/local_bh_enable() approach works only in case
> the IRQ handler is protected by a spinlock, but does not work if the
> IRQ handler is protected by mutex, i.e. this works for KS8851 with
> Parallel bus interface, but not for KS8851 with SPI bus interface.
>
> Remove the BH manipulation and instead of calling netif_rx() inside
> the IRQ handler code protected by the lock, queue all the received
> SKBs in the IRQ handler into a queue first, and once the IRQ handler
> exits the critical section protected by the lock, dequeue all the
> queued SKBs and push them all into netif_rx(). At this point, it is
> safe to trigger the net_rx_action() softirq, since the netif_rx()
> call is outside of the lock that protects the IRQ handler.
>
> Fixes: be0384bf599c ("net: ks8851: Handle softirqs at the end of IRQ thread to fix hang")
> Tested-by: Ronald Wahl <ronald.wahl@...itan.com> # KS8851 SPI
> Signed-off-by: Marek Vasut <marex@...x.de>

Reviewed-by: Eric Dumazet <edumazet@...gle.com>