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[195.250.132.146]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-488d5b3cbb2sm296253965e9.13.2026.04.13.02.40.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 13 Apr 2026 02:40:12 -0700 (PDT) Message-ID: <41e81533-0fd6-49f5-b7c1-b4e172affd2a@suse.com> Date: Mon, 13 Apr 2026 11:40:11 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] tracing: preserve module tracepoint strings To: Cao Ruichuang Cc: rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org References: <20260406170944.51047-1-create0818@163.com> <20260410051847.73259-1-create0818@163.com> Content-Language: en-US From: Petr Pavlu In-Reply-To: <20260410051847.73259-1-create0818@163.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/10/26 7:18 AM, Cao Ruichuang wrote: > tracepoint_string() is documented as exporting constant strings > through printk_formats, including when it is used from modules. > That currently does not work. > > A small test module that calls > tracepoint_string("tracepoint_string_test_module_string") loads > successfully and gets a pointer back, but the string never appears > in /sys/kernel/tracing/printk_formats. The loader only collects > __trace_printk_fmt from modules and ignores __tracepoint_str. > > Collect module __tracepoint_str entries too, copy them to stable > tracing-managed storage like module trace_printk formats, and let > trace_is_tracepoint_string() recognize those copied strings. This > makes module tracepoint strings visible through printk_formats and > keeps them accepted by the trace string safety checks. > > Update the tracepoint_string() documentation to describe this > module behavior explicitly, so the comment matches the preserved > module-string mappings exported by tracing. > > Link: https://bugzilla.kernel.org/show_bug.cgi?id=217196 > Signed-off-by: Cao Ruichuang > --- > v2: > - update tracepoint_string() documentation to describe the preserved > module-string mapping explicitly > - address Petr Pavlu's review about the comment not matching the > implemented module behavior I questioned in my previous comment whether the data associated with tracepoint_string() could be dropped when the module that created it is unloaded. Typically, modules should not leave any data behind when they are removed. Note how kernel/trace/trace_events.c tracks event fields using add_str_to_module() and releases them in trace_module_remove_events(). In practice, I suppose this isn't a large problem because the usage of tracepoint_string() is limited and one won't typically load/unload different modules that use this facility. Nonetheless, what is the reason for keeping the tracepoint_string() data for unloaded modules? -- Thanks, Petr