linux-kernel - Re: [PATCH net] net: sysfs: Fix deadlock situation in sysfs accesses

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Message-ID: <c1d52a7d-b6b2-4150-99c7-a67b2a127a18@csgroup.eu>
Date: Tue, 17 Dec 2024 17:18:40 +0100
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Andrew Lunn <andrew@...n.ch>
Cc: "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
 "Eric W. Biederman" <ebiederm@...ssion.com>, linux-kernel@...r.kernel.org,
 netdev@...r.kernel.org, Maxime Chevallier <maxime.chevallier@...tlin.com>,
 TRINH THAI Florent <florent.trinh-thai@...soprasteria.com>,
 CASAUBON Jean Michel <jean-michel.casaubon@...soprasteria.com>
Subject: Re: [PATCH net] net: sysfs: Fix deadlock situation in sysfs accesses

Le 17/12/2024 à 16:30, Andrew Lunn a écrit :
> On Tue, Dec 17, 2024 at 08:18:25AM +0100, Christophe Leroy wrote:
>> The following problem is encountered on kernel built with
>> CONFIG_PREEMPT. An snmp daemon running with normal priority is
>> regularly calling ioctl(SIOCGMIIPHY).
> 
> Why is an SNMP daemon using that IOCTL? What MAC driver is this? Is it
> using phylib? For phylib, that IOCTL is supposed to be for debug only,
> and is a bit of a foot gun. So i would not recommend it.
> 

That's the well-known Net-SNMP package.

See for instance 
https://github.com/net-snmp/net-snmp/blob/master/agent/mibgroup/if-mib/data_access/interface_linux.c#L954

The MAC is ucc_geth driver, it is phylib for the moment, it is being 
converted to phylink in net-next , see commit 53036aa8d031 ("net: 
freescale: ucc_geth: phylink conversion")

Christophe