On Wed, Jun 08, 2022 at 01:10:52AM +0900, Masami Hiramatsu (Google) wrote: > 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 LGTM Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx> jirka > > > kernel/trace/rethook.c | 9 +++++++++ > samples/fprobe/fprobe_example.c | 21 +++++++++++++++++---- > 2 files changed, 26 insertions(+), 4 deletions(-) > > -- > Signature
