linux-kernel - Re: [PATCH] tracing: fprobe: fix suspicious rcu usage in fprobe

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Message-ID: <aLfC0gZS_F3_srMT@gondor.apana.org.au>
Date: Wed, 3 Sep 2025 12:23:46 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Menglong Dong <dongml2@...natelecom.cn>, mhiramat@...nel.org,
	mathieu.desnoyers@...icios.com, linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org, oliver.sang@...el.com
Subject: Re: [PATCH] tracing: fprobe: fix suspicious rcu usage in fprobe_entry

On Tue, Sep 02, 2025 at 10:57:57AM -0400, Steven Rostedt wrote:
>
> And then have:
> 
>        quiet_rcu_read_lock_check();
>        head = rhltable_lookup(&fprobe_ip_table, &func, fprobe_rht_params);
>        quiet_rcu_read_unlock_check();

The thing is that rhl_for_each_entry_rcu which is called right after
your unlock above should have created the same warning as
rhltable_lookup.  The fact that it doesn't appears to be a bug:
it's using rcu_dereference_raw and I don't see why that's safe
at all.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt