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[82.192.244.13]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-435924ae723sm16436873f8f.41.2026.01.22.00.22.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Jan 2026 00:22:05 -0800 (PST) Sender: Salvatore Bonaccorso Received: by eldamar.lan (Postfix, from userid 1000) id 63C17BE2EE7; Thu, 22 Jan 2026 09:22:04 +0100 (CET) Date: Thu, 22 Jan 2026 09:22:04 +0100 From: Salvatore Bonaccorso To: Sudip Mukherjee Cc: Paul Menzel , Sudip Mukherjee , linux-kernel@vger.kernel.org, Andrew Morton , linux-mm@kvack.org, regressions@lists.linux.dev, Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Hans de Goede , Ilpo =?iso-8859-1?Q?J=E4rvinen?= , Giuseppe Sacco Subject: Re: BUG: kernel NULL pointer dereference, address: 0000000000000000 Message-ID: References: <6ba903ad-9897-42bb-8c2d-337385cc3746@molgen.mpg.de> <49cdd663-bcbd-48b4-ac38-77ce94ef0c8d@molgen.mpg.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Hi Sudip, On Sat, Jan 03, 2026 at 11:33:47AM +0000, Sudip Mukherjee wrote: > On Sat, Jan 03, 2026 at 12:01:19PM +0600, Paul Menzel wrote: > > Dear Salvatore, > > > > > > Thank you for the follow-up. > > > > Am 03.01.26 um 01:59 schrieb Salvatore Bonaccorso: > > > > > On Mon, Dec 01, 2025 at 05:05:59PM +0100, Paul Menzel wrote: > > > > > > Am 01.12.25 um 14:25 schrieb Sudip Mukherjee: > > > > > On Thu, 27 Nov 2025 at 22:55, Paul Menzel wrote: > > > > > > > > > > Am 27.11.25 um 19:51 schrieb Paul Menzel: > > > > > > > > > > > > > Unfortunately, not reproducible, but starting with Linux 6.18-rc7, I got > > > > > > > the oops below *once*: > > > > > > > > > https://bugs.debian.org/1124075 > > > > This is > > > > AMD AM5 ASUS ROG STRIX B650-A GAMING WIFI, BIOS 3067 12/10/2024 > > > > > https://bugs.debian.org/1124463 > > > > This is > > > > Dell Latitude E5470/0VHKV0, BIOS 1.34.3 11/20/2022 > > > > > Does it make a difference to cold-boot or reboot into the system? > > > > I only did cold boots, and I am not able to reproduce it anymore, and wrote > > it off to some hardware issue – despite the system working fine otherwise. > > > > I am adding the x86 folks, and regression lists. > > Thanks Salvatore for the Debian bug links. > > I had been trying to reproduce this but have not seen it on my machine so far. > > But looking at the traces from the Debian bugs and the trace from Paul, my best > guess is that its happening because the low level driver, parport_pc in these > cases, has not completed setting up the hardware. > > When 'lp' starts registering, parport driver will check if there is any port, > if no ports are found then it will try to load the low level module. > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/parport/share.c?h=v6.19-rc3#n198 > > As mentioned in the comment request_module() is not trying to load a real module > and it depends on the alias. Also, mentioned in the Documentation. > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/admin-guide/parport.rst?h=v6.19-rc3#n45 > > I am not sure why the problem is seen now, but is it possible to test the > below diff please and see if that fixes the issue. > > diff --git a/drivers/parport/share.c b/drivers/parport/share.c > index 427abdf3c4c4a..8f45daf7b3825 100644 > --- a/drivers/parport/share.c > +++ b/drivers/parport/share.c > @@ -287,8 +287,16 @@ int __parport_register_driver(struct parport_driver *drv, struct module *owner, > */ > ret = bus_for_each_dev(&parport_bus_type, NULL, NULL, > port_detect); > - if (!ret) > + > + /* Return if no port has been found. The driver has been > + * registered, so whenever a new port registers > + * attach_driver_chain() will be called which will then check > + * all registered drivers. > + */ > + if (!ret) { > get_lowlevel_driver(); > + return 0; > + } > > mutex_lock(®istration_lock); > if (drv->match_port) We had another report (https://bugs.debian.org/1126128_ but the problem remains here as well the reproducibilty. Uppon several reboots only the first one so far showed the problem and was not reproducible afterwards. Regards, Salvatore