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[2a01:cb08:fd:9b00:540e:212e:2ac4:9aae]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a099ae0ca4sm16128355f8f.14.2025.05.06.23.49.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 May 2025 23:49:19 -0700 (PDT) Message-ID: Subject: Re: [PATCH v2 2/2] tracing: protect trace_probe_log with mutex From: Paul Cacheux To: Steven Rostedt , Paul Cacheux via B4 Relay Cc: Masami Hiramatsu , Mathieu Desnoyers , Namhyung Kim , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Date: Wed, 07 May 2025 08:49:18 +0200 In-Reply-To: <20250502095025.1bc0426e@gandalf.local.home> References: <20250502-fix-trace-probe-log-race-v2-0-511ecc1521ec@gmail.com> <20250502-fix-trace-probe-log-race-v2-2-511ecc1521ec@gmail.com> <20250502095025.1bc0426e@gandalf.local.home> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.1 (3.56.1-1.fc42app2) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Fri, 2025-05-02 at 09:50 -0400, Steven Rostedt wrote: > On Fri, 02 May 2025 15:15:53 +0200 > Paul Cacheux via B4 Relay > wrote: >=20 > > From: Paul Cacheux > >=20 > > The shared trace_probe_log variable can be accessed and modified > > by multiple processes using tracefs at the same time, this new > > mutex will guarantee it's always in a coherent state. > >=20 > > There is no guarantee that multiple errors happening at the same > > time will each have the correct error message, but at least this > > won't crash. > >=20 > > Fixes: ab105a4fb894 ("tracing: Use tracing error_log with probe > > events") > >=20 >=20 > No space needed between Fixes and SOB. Sorry about that, fixed in v3 >=20 > > Signed-off-by: Paul Cacheux > > --- > > =C2=A0kernel/trace/trace_probe.c | 6 ++++++ > > =C2=A01 file changed, 6 insertions(+) > >=20 > > diff --git a/kernel/trace/trace_probe.c > > b/kernel/trace/trace_probe.c > > index > > 2eeecb6c95eea55502b83af6775b7b6f0cc5ab94..14a7a0b59cd20a8bc43e3e7c6 > > 53e986081f924c8 100644 > > --- a/kernel/trace/trace_probe.c > > +++ b/kernel/trace/trace_probe.c > > @@ -154,9 +154,11 @@ static const struct fetch_type > > *find_fetch_type(const char *type, unsigned long > > =C2=A0} > > =C2=A0 > > =C2=A0static struct trace_probe_log trace_probe_log; > > +static DEFINE_MUTEX(trace_probe_log_lock); >=20 > Probably should add a comment here saying something like: >=20 > /* > =C2=A0* The trace_probe_log_lock only protects against the individual > =C2=A0* modification of the trace_probe_log. It does not protect against > =C2=A0* the log from producing garbage if two probes use it at the same > =C2=A0* time. That would only happen if two admins were trying to add > =C2=A0* probes simultaneously which they shouldn't be doing. > =C2=A0*/ I sent a v3 with the space removed and this comment added, thank you for the review. >=20 > -- Steve >=20 >=20 > > =C2=A0 > > =C2=A0void trace_probe_log_init(const char *subsystem, int argc, const > > char **argv) > > =C2=A0{ > > + guard(mutex)(&trace_probe_log_lock); > > =C2=A0 trace_probe_log.subsystem =3D subsystem; > > =C2=A0 trace_probe_log.argc =3D argc; > > =C2=A0 trace_probe_log.argv =3D argv; > > @@ -165,11 +167,13 @@ void trace_probe_log_init(const char > > *subsystem, int argc, const char **argv) > > =C2=A0 > > =C2=A0void trace_probe_log_clear(void) > > =C2=A0{ > > + guard(mutex)(&trace_probe_log_lock); > > =C2=A0 memset(&trace_probe_log, 0, sizeof(trace_probe_log)); > > =C2=A0} > > =C2=A0 > > =C2=A0void trace_probe_log_set_index(int index) > > =C2=A0{ > > + guard(mutex)(&trace_probe_log_lock); > > =C2=A0 trace_probe_log.index =3D index; > > =C2=A0} > > =C2=A0 > > @@ -178,6 +182,8 @@ void __trace_probe_log_err(int offset, int > > err_type) > > =C2=A0 char *command, *p; > > =C2=A0 int i, len =3D 0, pos =3D 0; > > =C2=A0 > > + guard(mutex)(&trace_probe_log_lock); > > + > > =C2=A0 if (!trace_probe_log.argv) > > =C2=A0 return; > > =C2=A0 > >=20 Best regards, Paul Cacheux