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b=QmfbedIYDfCznU/qAZcKnNcBZ+C19RNjPp1M0SggWKes4puqwQGJeIjd3n3RtwXc2aNdrt WMYTXHCNIy/XcUCA== Date: Mon, 12 Oct 2026 12:04:35 +0200 From: Michal =?iso-8859-1?Q?Such=E1nek?= To: Amit Machhiwal Cc: Steven Rostedt , Masami Hiramatsu , linux-trace-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Mathieu Desnoyers , Madhavan Srinivasan , "Ritesh Harjani (IBM)" , Harsh Prateek Bora , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, Mark-PK Tsai , stable@vger.kernel.org Subject: Re: [PATCH 1/2] tracing: Do not initialize tracefs work if tracing is disabled Message-ID: References: <20261009163557.88467-1-amachhiw@linux.ibm.com> <20261009163557.88467-2-amachhiw@linux.ibm.com> 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=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20261009163557.88467-2-amachhiw@linux.ibm.com> X-Rspamd-Action: no action X-Spamd-Result: default: False [2.99 / 50.00]; BAYES_HAM(-3.00)[100.00%]; HFILTER_HOSTNAME_UNKNOWN(2.50)[]; SUSPICIOUS_RECIPS(1.50)[]; ONCE_RECEIVED(1.20)[]; RDNS_NONE(1.00)[]; HFILTER_HELO_IP_A(1.00)[kunlun.suse.cz]; NEURAL_HAM_LONG(-1.00)[-1.000]; HFILTER_HELO_NORES_A_OR_MX(0.30)[kunlun.suse.cz]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-0.977]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; RCPT_COUNT_TWELVE(0.00)[14]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_TRACE(0.00)[suse.de:+]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[goodmis.org,kernel.org,vger.kernel.org,lists.ozlabs.org,efficios.com,linux.ibm.com,gmail.com,mediatek.com]; DNSWL_BLOCKED(0.00)[2a07:de40:b306:2000::2:from]; TAGGED_RCPT(0.00)[]; RCVD_COUNT_ZERO(0.00)[0]; MISSING_XM_UA(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email,suse.de:dkim] X-Spam-Score: 2.99 X-Spam-Level: ** X-Spamd-Bar: ++ X-Rspamd-Queue-Id: 9ABD31F76C X-Spam-Flag: NO X-Rspamd-Server: rspamd2.dmz-prg2.suse.org On Fri, Oct 09, 2026 at 10:05:56PM +0530, Amit Machhiwal wrote: > If trace buffer allocation fails during early boot (e.g. in > early_trace_init() -> allocate_trace_buffers()), tracing_disabled is > left set to 1 and the global trace array events list remains > uninitialized. > > Later during boot, tracer_init_tracefs() (invoked via fs_initcall) > queues tracerfs_init_work asynchronously without checking if tracing was > disabled. When tracer_init_tracefs_work_func() runs, it calls > event_trace_init() and init_tracer_tracefs(&global_trace, NULL) > unconditionally. This leads to __find_event_file() dereferencing an > uninitialized tr->events list, causing an early boot NULL pointer > dereference Oops: > > BUG: Kernel NULL pointer dereference on read at 0x00000010 > Faulting instruction address: 0xc000000000485be0 > Oops: Kernel access of bad area, sig: 7 [#1] > ... > NIP [c000000000485be0] __find_event_file+0x70/0x3c0 > LR [c000000000448874] init_tracer_tracefs+0x274/0xc80 > Call Trace: > init_tracer_tracefs+0x274/0xc80 > tracer_init_tracefs_work_func+0x50/0x320 > process_one_work+0x1e8/0x5c0 > worker_thread+0x1dc/0x3d0 > kthread+0x194/0x1b0 > start_kernel_thread+0x14/0x18 > > Check tracing_disabled at the beginning of tracer_init_tracefs_work_func() > and return immediately if tracing is disabled or failed to initialize, > preventing the crash. Thanks for the patch Tested-by: Michal Suchánek > > Fixes: 6621a7004684 ("tracing: make tracer_init_tracefs initcall asynchronous") > Cc: stable@vger.kernel.org > Reported-by: Michal Suchánek > Closes: https://lore.kernel.org/all/arYskzbiaNzBR9MD@kunlun.suse.cz/ > Signed-off-by: Amit Machhiwal > --- > kernel/trace/trace.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index e4a490d3d08c..7ac9e1c92702 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -9287,6 +9287,12 @@ static struct notifier_block trace_module_nb = { > > static __init void tracer_init_tracefs_work_func(struct work_struct *work) > { > + /* > + * Do not attempt to initialize tracefs if tracing was disabled or > + * failed to allocate > + */ > + if (tracing_disabled) > + return; > > event_trace_init(); > > -- > 2.54.0 (Apple Git-157) >