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[80.218.24.251]) by smtp.gmail.com with ESMTPSA id c1sm102702edn.62.2019.08.11.08.33.27 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Sun, 11 Aug 2019 08:33:27 -0700 (PDT) Date: Sun, 11 Aug 2019 17:33:26 +0200 From: Salvatore Bonaccorso To: Thomas Gleixner Cc: Paul Menzel , Jacob Pan , Len Brown , x86@kernel.org, LKML , linux-pm@vger.kernel.org, Steven Rostedt , Matthew Garrett Subject: Re: [Linux 5.2.x] /sys/kernel/debug/tracing/events/power/cpu_idle/id: BUG: kernel NULL pointer dereference, address: 0000000000000000 Message-ID: <20190811153326.GA8036@eldamar.local> References: <4b54ff1e-f18b-3c58-7caa-945a0775c24c@molgen.mpg.de> <01c7bc6b-dc6d-5eca-401a-8869e02f7c2a@molgen.mpg.de> <20190811094630.GA18925@eldamar.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org Thomas, On Sun, Aug 11, 2019 at 02:58:15PM +0200, Thomas Gleixner wrote: > Salvatore, > > On Sun, 11 Aug 2019, Salvatore Bonaccorso wrote: > > On Sun, Aug 11, 2019 at 08:22:35AM +0200, Thomas Gleixner wrote: > > > On Sat, 10 Aug 2019, Paul Menzel wrote: > > > > For the record. It is also reproducible with Linux 5.2.6, and trying to print > > > > the file contents with cat already fails. > > > > > > > > ``` > > > > $ sudo ls -l /sys/kernel/debug/tracing/events/power/cpu_idle/id > > > > -r--r--r-- 1 root root 0 Aug 10 23:05 > > > > /sys/kernel/debug/tracing/events/power/cpu_idle/id > > > > $ sudo cat /sys/kernel/debug/tracing/events/power/cpu_idle/id > > > > Killed > > > > ``` > > > > This seems to be related to https://bugs.debian.org/934304 (in > > particular https://bugs.debian.org/934304#29). The mentioned patch > > features/all/lockdown/0031-tracefs-Restrict-tracefs-when-the-kernel-is-locked-d.patch > > is a backport of https://patchwork.kernel.org/patch/11069661/ with > > only change that it is converted back to the non-LSM lockdown API. > > So that's a debian kernel specific issue? "yes". A kernel build without the above patch does not exhibit the issue. So the issue is specific to that lockdown patch ("tracefs: Restrict tracefs when the kernel is locked down"). Steven and Matthew are both CC'ed. Regards, Salvatore