On Fri, 9 May 2025 16:30:08 +0200
Matthieu Baerts [off-list ref] wrote:

Hi Breno,

On 10/04/2025 14:22, Breno Leitao wrote:

quoted

When CONFIG_PROVE_RCU_LIST is enabled, fprobe triggers the following
warning:

    WARNING: suspicious RCU usage
    kernel/trace/fprobe.c:457 RCU-list traversed in non-reader section!!

    other info that might help us debug this:
	#1: ffffffff863c4e08 (fprobe_mutex){+.+.}-{4:4}, at: fprobe_module_callback+0x7b/0x8c0

    Call Trace:
	fprobe_module_callback
	notifier_call_chain
	blocking_notifier_call_chain

This warning occurs because fprobe_remove_node_in_module() traverses an
RCU list using RCU primitives without holding an RCU read lock. However,
the function is only called from fprobe_module_callback(), which holds
the fprobe_mutex lock that provides sufficient protection for safely
traversing the list.

Fix the warning by specifying the locking design to the
CONFIG_PROVE_RCU_LIST mechanism. Add the lockdep_is_held() argument to
hlist_for_each_entry_rcu() to inform the RCU checker that fprobe_mutex
provides the required protection.

@Breno: thank you for the patch, I have it applied for a while on a
branch dedicated to our CI to avoid false positive reports.

Tested-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>

Oops, I missed this patch.

Let me pick it up and send it urgently.

Thank you,

Hopefully this fix can be sent to Linus before the v6.15 release :)

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.

-- 
Masami Hiramatsu (Google) [off-list ref]