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> --- 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
