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[188.141.5.72]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4abea72254csm82768725e9.1.2026.10.31.14.04.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 31 Oct 2026 14:04:23 -0700 (PDT) From: David Carlier To: Steven Rostedt , Masami Hiramatsu Cc: Mathieu Desnoyers , linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org, David Carlier , stable@vger.kernel.org Subject: [PATCH] tracing/user_events: Don't free an event that a dynamic event still references Date: Sat, 31 Oct 2026 21:03:59 +0000 Message-ID: <20261031210420.501187-1-devnexen@gmail.com> X-Mailer: git-send-email 2.55.0 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit An eprobe takes a reference on the call of the event it attaches to, and kprobe, uprobe, fprobe and synth events all refuse to go away while trace_event_dyn_busy() says such a reference exists. user_events never checks it, so a user event can be freed under an eprobe: echo 'u:test u32 a' >> dynamic_events echo 'e:ep user_events/test a=$a' >> dynamic_events echo '-:user_events/test' >> dynamic_events echo '-:eprobes/ep' >> dynamic_events The last write drops the reference on the freed call. Return -EBUSY from destroy_user_event() in that case. Fixes: 7f5a08c79df3 ("user_events: Add minimal support for trace_event into ftrace") Cc: stable@vger.kernel.org Signed-off-by: David Carlier --- A non-persistent event whose last fd closes while an eprobe holds it now stays registered after the eprobe is gone. Can follow up with a retry on the eprobe put if wanted. kernel/trace/trace_events_user.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c index f658c3a77aa7..49b857a7f1d7 100644 --- a/kernel/trace/trace_events_user.c +++ b/kernel/trace/trace_events_user.c @@ -1506,6 +1506,10 @@ static int destroy_user_event(struct user_event *user) lockdep_assert_held(&event_mutex); + /* If there is a reference to a dynamic event */ + if (trace_event_dyn_busy(&user->call)) + return -EBUSY; + /* * Detach the fields before removing the call. Removing the event * frees the field list memory (trace_destroy_fields() is run on -- 2.55.0