tracing: Do not initialize tracefs work if tracing is disabled

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.

Cc: stable@vger.kernel.org
Fixes: 6621a7004684 ("tracing: make tracer_init_tracefs initcall asynchronous")
Link: https://patch.msgid.link/20261009163557.88467-2-amachhiw@linux.ibm.com
Reported-by: Michal Suchánek <msuchanek@suse.de>
Closes: https://lore.kernel.org/all/arYskzbiaNzBR9MD@kunlun.suse.cz/
Signed-off-by: Amit Machhiwal <amachhiw@linux.ibm.com>
Tested-by: Michal Suchánek <msuchanek@suse.de>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

0 files changed, 0 insertions, 0 deletions