Hi, Here is the 2nd version of the patches to reject rethook if RCU is not watching. The 1st version is here; https://lore.kernel.org/all/165189881197.175864.14757002789194211860.stgit@devnote2/ This is actually related to the idle function tracing issue reported by Jiri on LKML (*) (*) https://lore.kernel.org/bpf/20220515203653.4039075-1-jolsa@xxxxxxxxxx/ Jiri reported that fprobe (and rethook) based kprobe-multi bpf trace kicks "suspicious RCU usage" warning. This is because the RCU operation is used in the kprobe-multi handler. However, I also found that the similar issue exists in the rethook because the rethook uses RCU operation. I added a new patch [1/2] to test this issue by fprobe_example.ko. (with this patch, it can avoid using printk() which also involves the RCU operation.) ------ # insmod fprobe_example.ko symbol=arch_cpu_idle use_trace=1 stackdump=0 fprobe_init: Planted fprobe at arch_cpu_idle # rmmod fprobe_example.ko ============================= WARNING: suspicious RCU usage 5.18.0-rc5-00019-gcae4ec21e87a-dirty #30 Not tainted ----------------------------- include/trace/events/lock.h:37 suspicious rcu_dereference_check() usage! other info that might help us debug this: rcu_scheduler_active = 2, debug_locks = 1 RCU used illegally from extended quiescent state! no locks held by swapper/0/0. stack backtrace: CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.18.0-rc5-00019-gcae4ec21e87a-dirty #30 ------ After applying [2/2] fix (which avoid initializing rethook on function entry if !rcu_watching()), this warning was gone. ------ # insmod fprobe_example.ko symbol=arch_cpu_idle use_trace=1 stackdump=0 fprobe_init: Planted fprobe at arch_cpu_idle # rmmod fprobe_example.ko fprobe_exit: fprobe at arch_cpu_idle unregistered. 225 times hit, 230 times missed ------ Note that you can test this program until the arch_cpu_idle() is marked as noinstr. After that, the function can not be traced. Thank you, --- Masami Hiramatsu (Google) (2): fprobe: samples: Add use_trace option and show hit/missed counter rethook: Reject getting a rethook if RCU is not watching kernel/trace/rethook.c | 9 +++++++++ samples/fprobe/fprobe_example.c | 21 +++++++++++++++++---- 2 files changed, 26 insertions(+), 4 deletions(-) -- Signature
