On Thu, 4 Sep 2025 14:27:29 +0800 Menglong Dong <menglong8.d...@gmail.com> wrote:
> rcu_read_lock() is not needed in fprobe_entry, but rcu_dereference_check() > is used in rhltable_lookup(), which causes suspicious RCU usage warning: > > WARNING: suspicious RCU usage > 6.17.0-rc1-00001-gdfe0d675df82 #1 Tainted: G S > ----------------------------- > include/linux/rhashtable.h:602 suspicious rcu_dereference_check() usage! > ...... > stack backtrace: > CPU: 1 UID: 0 PID: 4652 Comm: ftracetest Tainted: G S > Tainted: [S]=CPU_OUT_OF_SPEC, [I]=FIRMWARE_WORKAROUND > Hardware name: Dell Inc. OptiPlex 7040/0Y7WYT, BIOS 1.1.1 10/07/2015 > Call Trace: > <TASK> > dump_stack_lvl+0x7c/0x90 > lockdep_rcu_suspicious+0x14f/0x1c0 > __rhashtable_lookup+0x1e0/0x260 > ? __pfx_kernel_clone+0x10/0x10 > fprobe_entry+0x9a/0x450 > ? __lock_acquire+0x6b0/0xca0 > ? find_held_lock+0x2b/0x80 > ? __pfx_fprobe_entry+0x10/0x10 > ? __pfx_kernel_clone+0x10/0x10 > ? lock_acquire+0x14c/0x2d0 > ? __might_fault+0x74/0xc0 > function_graph_enter_regs+0x2a0/0x550 > ? __do_sys_clone+0xb5/0x100 > ? __pfx_function_graph_enter_regs+0x10/0x10 > ? _copy_to_user+0x58/0x70 > ? __pfx_kernel_clone+0x10/0x10 > ? __x64_sys_rt_sigprocmask+0x114/0x180 > ? __pfx___x64_sys_rt_sigprocmask+0x10/0x10 > ? __pfx_kernel_clone+0x10/0x10 > ftrace_graph_func+0x87/0xb0 > > As we discussed in [1], fix this by using guard(rcu)() in fprobe_entry() > to protect the rhltable_lookup() and rhl_for_each_entry_rcu() with > rcu_read_lock and suppress this warning. > > Link: > https://lore.kernel.org/all/20250829021436.19982-1-dong...@chinatelecom.cn/ > [1] > Reported-by: kernel test robot <oliver.s...@intel.com> > Closes: https://lore.kernel.org/oe-lkp/202508281655.54c87330-...@intel.com > Fixes: dfe0d675df82 ("tracing: fprobe: use rhltable for fprobe_ip_table") > Signed-off-by: Menglong Dong <dong...@chinatelecom.cn> Looks good to me. Let me pick this to probes/for-next. Thanks! > --- > v2: > - use guard(rcu)() instead of rcu_read_lock() > --- > kernel/trace/fprobe.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c > index fb127fa95f21..6a205903b1ed 100644 > --- a/kernel/trace/fprobe.c > +++ b/kernel/trace/fprobe.c > @@ -269,6 +269,7 @@ static int fprobe_entry(struct ftrace_graph_ent *trace, > struct fgraph_ops *gops, > if (WARN_ON_ONCE(!fregs)) > return 0; > > + guard(rcu)(); > head = rhltable_lookup(&fprobe_ip_table, &func, fprobe_rht_params); > reserved_words = 0; > rhl_for_each_entry_rcu(node, pos, head, hlist) { > -- > 2.51.0 > -- Masami Hiramatsu (Google) <mhira...@kernel.org>
