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[195.250.132.146]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43796a6ba57sm22103738f8f.15.2026.02.16.05.43.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 16 Feb 2026 05:43:09 -0800 (PST) From: Petr Pavlu To: Steven Rostedt , Masami Hiramatsu Cc: Mathieu Desnoyers , Tom Zanussi , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Petr Pavlu Subject: [PATCH v2 1/4] tracing: Fix checking of freed trace_event_file for hist files Date: Mon, 16 Feb 2026 14:41:57 +0100 Message-ID: <20260216134247.1311631-2-petr.pavlu@suse.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260216134247.1311631-1-petr.pavlu@suse.com> References: <20260216134247.1311631-1-petr.pavlu@suse.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The event_hist_open() and event_hist_poll() functions currently retrieve a trace_event_file pointer from a file struct by invoking event_file_data(), which simply returns file->f_inode->i_private. The functions then check if the pointer is NULL to determine whether the event is still valid. This approach is flawed because i_private is assigned when an eventfs inode is allocated and remains set throughout its lifetime. Instead, the code should call event_file_file(), which checks for EVENT_FILE_FL_FREED. Using the incorrect access function may result in the code potentially opening a hist file for an event that is being removed or becoming stuck while polling on this file. A related issue is that although event_hist_poll() attempts to verify whether an event file is being removed, this check may not occur or could be unnecessarily delayed. This happens because hist_poll_wakeup() is currently invoked only from event_hist_trigger() when a hist command is triggered. If the event file is being removed, no associated hist command will be triggered and a waiter will be woken up only after an unrelated hist command is triggered. Fix these issues by changing the access method to event_file_file() and adding a call to hist_poll_wakeup() in remove_event_file_dir() after setting the EVENT_FILE_FL_FREED flag. This ensures that a task polling on a hist file is woken up and receives EPOLLERR. Fixes: 1bd13edbbed6 ("tracing/hist: Add poll(POLLIN) support on hist file") Signed-off-by: Petr Pavlu Acked-by: Masami Hiramatsu (Google) --- include/linux/trace_events.h | 5 +++++ kernel/trace/trace_events.c | 3 +++ kernel/trace/trace_events_hist.c | 4 ++-- 3 files changed, 10 insertions(+), 2 deletions(-) diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h index 3690221ba3d8..f925034e402d 100644 --- a/include/linux/trace_events.h +++ b/include/linux/trace_events.h @@ -683,6 +683,11 @@ static inline void hist_poll_wakeup(void) =20 #define hist_poll_wait(file, wait) \ poll_wait(file, &hist_poll_wq, wait) + +#else +static inline void hist_poll_wakeup(void) +{ +} #endif =20 #define __TRACE_EVENT_FLAGS(name, value) \ diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index 137b4d9bb116..e8ed6ba155cf 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -1295,6 +1295,9 @@ static void remove_event_file_dir(struct trace_event_= file *file) free_event_filter(file->filter); file->flags |=3D EVENT_FILE_FL_FREED; event_file_put(file); + + /* Wake up hist poll waiters to notice the EVENT_FILE_FL_FREED flag. */ + hist_poll_wakeup(); } =20 /* diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_h= ist.c index c97bb2fda5c0..744c2aa3d668 100644 --- a/kernel/trace/trace_events_hist.c +++ b/kernel/trace/trace_events_hist.c @@ -5778,7 +5778,7 @@ static __poll_t event_hist_poll(struct file *file, st= ruct poll_table_struct *wai =20 guard(mutex)(&event_mutex); =20 - event_file =3D event_file_data(file); + event_file =3D event_file_file(file); if (!event_file) return EPOLLERR; =20 @@ -5816,7 +5816,7 @@ static int event_hist_open(struct inode *inode, struc= t file *file) =20 guard(mutex)(&event_mutex); =20 - event_file =3D event_file_data(file); + event_file =3D event_file_file(file); if (!event_file) { ret =3D -ENODEV; goto err; --=20 2.52.0