From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 C52092EA732; Thu, 23 Jul 2026 21:33:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784842399; cv=none; b=KmDaBP6TJLfSQZPR6mye0mwfH7t0M7sxOoClVzq7JmQhCNqG1SiDYxfIgWs97KmHP4W4I/uQWorxHlyzPTNDp4xZ2c6ld481mOAkjMzGXUNF01MANuJGrVxgCt3eXK52NA5D+Uwg7trfZgns1nCRCxMIph8xKcSZPIIf8pr9yws= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784842399; c=relaxed/simple; bh=XaDNRLjYwCK+tn3+UWU4Gc2rHSUWBZaSi4llDs+EWPo=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=g47BDnJJ2zxpfNkl1Yo74rqQW/I0Okt0JINs76zC7oz39mBzHtCEM6ElpYlGPs2TE4RM69PLepVKo6uFbbyp+3eoz97q55A004jWD9EGdfqSXM4MmACGdvOiljIun7VxzPOGblUy4346nWsKKKdnQTseY/43P2WHU5KYit+hZGg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=dB9U78n5; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="dB9U78n5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 643D21F000E9; Thu, 23 Jul 2026 21:33:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784842398; bh=Q+/dGfsl+8WV+jjjuXy5AIteLaMiC7aLzoVrAVtVS90=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=dB9U78n5WvACrMUHbKZhUKldiHJ3E/9Fvdsb08QvyTfE7N18wA2gmd//EG9b5rke2 N1hMv60ffSam/zK6euodWKccFF11Di6Fefwxbp2j36vwb+VGKRtOFNYAt3Wm22O49v J5AHN+p4mKc7bDiS3hu2iJBdPsxCMDQxEaKiI2dc74/w+3fu8tF/65F7MNllavp+Id lyBQn6dDrzR35Nh+fHP7IWVctw+MNKMbVy+fvjKm7cE2w9otk4PJkt09cWhCuJ9Rab ZopT1diXB7M7mMJgzi8Rk9xmcGYeFDfNfBC5w5EzRoUl5rgS3GkayetX95qwipRQCp 1kv7rdON69jZw== Date: Fri, 24 Jul 2026 06:33:15 +0900 From: Masami Hiramatsu (Google) To: David Carlier Cc: Steven Rostedt , Mathieu Desnoyers , linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] tracing: Restore synchronize_rcu() before freeing trigger private data Message-Id: <20260724063315.b5ab5f8519c1555fa0d49756@kernel.org> In-Reply-To: <20260723170212.55325-1-devnexen@gmail.com> References: <20260723170212.55325-1-devnexen@gmail.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Thu, 23 Jul 2026 18:02:12 +0100 David Carlier wrote: > Commit 61d445af0a7c ("tracing: Add bulk garbage collection of freeing > event_trigger_data") moved the kfree() of event_trigger_data to a kthread > that runs tracepoint_synchronize_unregister() before freeing. That removed > the synchronize_rcu() the trigger .free callbacks used to get implicitly and > inline from trigger_data_free(). > > event_hist_trigger_free(), event_hist_trigger_named_free() and > event_enable_trigger_free() free their satellite data (hist_data, cmd_ops, > enable_data) right after trigger_data_free() returns. With the synchronize > now deferred to the kthread, a concurrent tracepoint handler can still reach > that data through the list_del_rcu()'d trigger, causing a use-after-free. > > The teardown must also stay synchronous for correctness: the histogram > cleanup (remove_hist_vars(), unregister_field_var_hists()) has to detach a > synthetic event from the histogram before the trigger-removal write returns. > Deferring it lets a following command race in and fail the synthetic-event > removal with -EBUSY, as caught by > tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-synthetic-eprobe.tc. > > Call synchronize_rcu() directly before freeing the satellite data instead. > > Suggested-by: Steven Rostedt > Fixes: 61d445af0a7c ("tracing: Add bulk garbage collection of freeing event_trigger_data") > Signed-off-by: David Carlier Hi David, Instead of adding just a synchronize_rcu(), can you reconsider to introduce .private_data_free() to event_trigger_data? I hit the same issue on wprobe and fixed it with ".private_free()" (I think private_data_free() is better naming) https://patchwork.kernel.org/project/linux-trace-kernel/patch/178476144141.26117.8004746214529353062.stgit@devnote2/ Thank you, > --- > kernel/trace/trace_events_hist.c | 3 +++ > kernel/trace/trace_events_trigger.c | 1 + > 2 files changed, 4 insertions(+) > > diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c > index 82ce492ab268..ddd2f70dac4f 100644 > --- a/kernel/trace/trace_events_hist.c > +++ b/kernel/trace/trace_events_hist.c > @@ -6349,6 +6349,8 @@ static void event_hist_trigger_free(struct event_trigger_data *data) > > trigger_data_free(data); > > + synchronize_rcu(); > + > remove_hist_vars(hist_data); > > unregister_field_var_hists(hist_data); > @@ -6388,6 +6390,7 @@ static void event_hist_trigger_named_free(struct event_trigger_data *data) > > del_named_trigger(data); > trigger_data_free(data); > + synchronize_rcu(); > kfree(cmd_ops); > } > } > diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c > index 655db2e82513..c3f54f2540b6 100644 > --- a/kernel/trace/trace_events_trigger.c > +++ b/kernel/trace/trace_events_trigger.c > @@ -1730,6 +1730,7 @@ void event_enable_trigger_free(struct event_trigger_data *data) > trace_event_enable_disable(enable_data->file, 0, 1); > trace_event_put_ref(enable_data->file->event_call); > trigger_data_free(data); > + synchronize_rcu(); > kfree(enable_data); > } > } > -- > 2.53.0 > -- Masami Hiramatsu (Google)