netdev - Re: Bug#1126015: linux-image-6.17.13+deb14-rt-amd64: ethtool -x <sfc-net-driver-ifname> causes: rtmutex deadlock detected

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Message-ID: <1bb7607e-b078-4e30-bae3-9d9a8ab627f2@gmail.com>
Date: Thu, 22 Jan 2026 20:11:53 +0000
From: Edward Cree <ecree.xilinx@...il.com>
To: Ben Hutchings <ben@...adent.org.uk>,
 Salvatore Bonaccorso <carnil@...ian.org>, linux-net-drivers@....com
Cc: 1126015@...s.debian.org, Damir Mansurov <damir.mansurov@...etlabs.ru>,
 netdev <netdev@...r.kernel.org>
Subject: Re: Bug#1126015: linux-image-6.17.13+deb14-rt-amd64: ethtool -x
 <sfc-net-driver-ifname> causes: rtmutex deadlock detected

On 21/01/2026 12:39, Ben Hutchings wrote:
> The deadlock seems to be quite straightforward:
> 
> 1. In net/ethtool/rss.c, rss_prepare_get() locks the net device's
>    rss_lock and calls its driver's get_rxfh operation
> 2. In drivers/net/ethernet/sfc/ethtool_common.c, efx_ethtool_get_rxfh()
>    calls the chip's rx_pull_rss_config operation
> 3. In drivers/net/ethernet/sfc/mcdi_filters.c,
>    efx_mcdi_rx_pull_rss_config() locks the net device's rss_lock
> 
> Step 3 seems to be a workaround for missing locking in the ethtool core.
> Since that locking was added to the ethtool core in 6.17, it needs to be
> removed from the sfc driver from that version onward.

Analysis looks correct to me.  I think the appropriate Fixes tag is
040cef30b5e6 ("net: ethtool: move get_rxfh callback under the rss_lock")

Unless you want to do it, I'll post a patch with Damir's Reported-by:
 and your Suggested-by:.

-ed