From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 73BC0239085; Tue, 24 Mar 2026 19:02:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=216.40.44.15 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774378968; cv=none; b=G5MlY7DK2nQpPrhnmlgnpVnrCruCaDFwCbyjEHQzLjHrbf4YdTX9EEOat8ghrRgDPfSdZOYOC7ikw+gGohPGsMyH1H1aLYd1cJdu19mAfKrPdF//WoVWVjUKq/NpkabSxq+fC3x+k4qBF0UCRnSegl9bunqVYmA61PkQULSKo1I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774378968; c=relaxed/simple; bh=pLADkz47Gi6G2xqFECg+KAw/tEwaX0Gk5QNHrL+Ja1Y=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=Qwj94lsdaL/8zYkzVhexNMJcpDZpGeteb+wIws6Ua5juJ5vE/+S59fnusasg5wyXUquCe350nCwzoa/hr5xKWCssw229Se4T7KIYM6D8VoFf3WMUrU7uAwzaRHk0cVtgKNmPSM3oz/2WQlQzVo5aTlXHSo/OcUJQU+0sepGit5U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org; spf=pass smtp.mailfrom=goodmis.org; arc=none smtp.client-ip=216.40.44.15 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=goodmis.org Received: from omf10.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 84DAE5875A; Tue, 24 Mar 2026 18:53:07 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: rostedt@goodmis.org) by omf10.hostedemail.com (Postfix) with ESMTPA id 52DDE41; Tue, 24 Mar 2026 18:53:05 +0000 (UTC) Date: Tue, 24 Mar 2026 14:53:47 -0400 From: Steven Rostedt To: Wesley Atwell Cc: mhiramat@kernel.org, mark.rutland@arm.com, mathieu.desnoyers@efficios.com, corbet@lwn.net, skhan@linuxfoundation.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH v3 2/2] tracing: drain deferred trigger frees if kthread startup fails Message-ID: <20260324145347.29d8ee75@gandalf.local.home> In-Reply-To: <20260310064715.527906-3-atwellwea@gmail.com> References: <20260310064715.527906-1-atwellwea@gmail.com> <20260310064715.527906-3-atwellwea@gmail.com> X-Mailer: Claws Mail 3.20.0git84 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspamout07 X-Rspamd-Queue-Id: 52DDE41 X-Stat-Signature: h4pojkar4dzkwehjisye7c5wxpt4quig X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX1/vYR1P7wsVSGfjTF+LiWTz9Xhq3KtXLDM= X-HE-Tag: 1774378385-130353 X-HE-Meta: U2FsdGVkX18tIg+/ueuE6N8C+J4Sz7foWLk1VvuUjnOaZh7FLK7zbHJIigaaB5b068hpdbfAqgutQcCOJ6CqnQngiSBac0OHyJ0JqBLh/VM8doqmQZ7J5q0vUOLIHV1Tt70j7jN0VglEfp/M49PNQwlFUaTclhFze+F4fEh02aLm5iQBaVa33ylkHOgVXKPObmmJ5xWiBbGdeOw+sbPSbitaEbd+EdmmbiM926C21jCuSz/JQ9yY3PBjtLPd0Dt7Vz/W47XSE48LgR6riKL5/pYY1gnlVl3N6uEZKju/haZD8cUHgVwNnI8m50rXDGRhmoIE4aftqXDHpJlfF3aWxsYE5Z/vAxHA On Tue, 10 Mar 2026 00:47:15 -0600 Wesley Atwell wrote: > Boot-time trigger registration can fail before the trigger-data cleanup > kthread exists. Deferring those frees until late init is fine, but the > post-boot fallback must still drain the deferred list if kthread > creation never succeeds. > > Otherwise, boot-deferred nodes can accumulate on > trigger_data_free_list, later frees fall back to synchronously freeing > only the current object, and the older queued entries are leaked > forever. > > Keep the deferred boot-time behavior, but when kthread creation fails, > drain the whole queued list synchronously. Do the same in the late-init > drain path so queued entries are not stranded there either. > > Fixes: 61d445af0a7c ("tracing: Add bulk garbage collection of freeing event_trigger_data") > Signed-off-by: Wesley Atwell > --- > kernel/trace/trace_events_trigger.c | 79 ++++++++++++++++++++++++----- > 1 file changed, 66 insertions(+), 13 deletions(-) > > diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c > index d5230b759a2d..428b46272ac8 100644 > --- a/kernel/trace/trace_events_trigger.c > +++ b/kernel/trace/trace_events_trigger.c > @@ -22,6 +22,39 @@ static struct task_struct *trigger_kthread; > static struct llist_head trigger_data_free_list; > static DEFINE_MUTEX(trigger_data_kthread_mutex); > > +static int trigger_kthread_fn(void *ignore); > + > +static void trigger_start_kthread_locked(void) > +{ > + lockdep_assert_held(&trigger_data_kthread_mutex); > + > + if (!trigger_kthread) { > + struct task_struct *kthread; > + > + kthread = kthread_create(trigger_kthread_fn, NULL, > + "trigger_data_free"); This only creates the thread and doesn't start it. The function name is confusing. Please change it to: trigger_create_kthread_locked() > + if (!IS_ERR(kthread)) > + WRITE_ONCE(trigger_kthread, kthread); > + } > +} > + > +static void trigger_data_free_queued_locked(void) > +{ > + struct event_trigger_data *data, *tmp; > + struct llist_node *llnodes; > + > + lockdep_assert_held(&trigger_data_kthread_mutex); > + > + llnodes = llist_del_all(&trigger_data_free_list); > + if (!llnodes) > + return; > + > + tracepoint_synchronize_unregister(); > + > + llist_for_each_entry_safe(data, tmp, llnodes, llist) > + kfree(data); > +} > + > /* Bulk garbage collection of event_trigger_data elements */ > static int trigger_kthread_fn(void *ignore) > { > @@ -56,30 +89,50 @@ void trigger_data_free(struct event_trigger_data *data) > if (data->cmd_ops->set_filter) > data->cmd_ops->set_filter(NULL, data, NULL); > > + /* > + * Boot-time trigger registration can fail before kthread creation > + * works. Keep the deferred-free semantics during boot and let late > + * init start the kthread to drain the list. > + */ > + if (system_state == SYSTEM_BOOTING && !trigger_kthread) { > + llist_add(&data->llist, &trigger_data_free_list); > + return; > + } > + > if (unlikely(!trigger_kthread)) { > guard(mutex)(&trigger_data_kthread_mutex); > + > + trigger_start_kthread_locked(); > /* Check again after taking mutex */ > if (!trigger_kthread) { > - struct task_struct *kthread; > - > - kthread = kthread_create(trigger_kthread_fn, NULL, > - "trigger_data_free"); > - if (!IS_ERR(kthread)) > - WRITE_ONCE(trigger_kthread, kthread); > + llist_add(&data->llist, &trigger_data_free_list); > + /* Drain the queued frees synchronously if startup failed. */ s/startup/creation/ > + trigger_data_free_queued_locked(); > + return; > } > } -- Steve > > - if (!trigger_kthread) { > - /* Do it the slow way */ > - tracepoint_synchronize_unregister(); > - kfree(data); > - return; > - } > - > llist_add(&data->llist, &trigger_data_free_list); > wake_up_process(trigger_kthread); > } > > +static int __init trigger_data_free_init(void) > +{ > + guard(mutex)(&trigger_data_kthread_mutex); > + > + if (llist_empty(&trigger_data_free_list)) > + return 0; > + > + trigger_start_kthread_locked(); > + if (trigger_kthread) > + wake_up_process(trigger_kthread); > + else > + trigger_data_free_queued_locked(); > + > + return 0; > +} > +late_initcall(trigger_data_free_init); > + > static inline void data_ops_trigger(struct event_trigger_data *data, > struct trace_buffer *buffer, void *rec, > struct ring_buffer_event *event)