[PATCH 0/3] probes: Use trace_printk() in probe handlers

["Masami Hiramatsu (Google)" <mhiramat@kernel.org>]

Hi,

Here are patches to update the probe sample code to use trace_printk
instead of normal printk. Since the fprobe and kprobe/kretprobe handlers
can be called from somewhere where console is locked, using printk() is
basically unsafe. Only the unoptimized kprobe on x86 is safe because it
is ran with NMI context (in this case, the kernel uses printk_deferred()
automatically), but optimized kprobe/kretprobe/fprobe are not.

Thus, this series replaces those printk() (pr_*()) with trace_printk()
which should be safe to output the result into trace buffer, and use
trace_dump_stack() instead of stack_trace_print().

The similar issue had been reported by Tiezhu Yang [1] in 2023, but
it was pointed different reason, and not applicable to upstream.
I investigated it again.

[1] https://lore.kernel.org/all/d179086d-78d8-d0e3-e113-9072cffa55f4@loongson.cn/

Thank you,
---
base-commit: bc71431221f5ba8bb33918399552636e059c2c45

Masami Hiramatsu (Google) (3):
      samples/kprobes: Use trace_printk() in probe handlers
      samples/fprobe: Use trace_printk() and trace_dump_stack()
      docs: trace: Warn against using printk() in probe handlers


 Documentation/trace/fprobe.rst      |    5 +++
 Documentation/trace/kprobes.rst     |   11 +++++-
 samples/Kconfig                     |    4 +-
 samples/fprobe/fprobe_example.c     |   49 +++++--------------------
 samples/kprobes/kprobe_example.c    |   69 ++++++++++++++++++-----------------
 samples/kprobes/kretprobe_example.c |   10 +++--
 6 files changed, 66 insertions(+), 82 deletions(-)

--
Masami Hiramatsu (Google) <mhiramat@kernel.org>