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 15BD329E0FD; Thu, 21 May 2026 13:47:03 +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=1779371225; cv=none; b=RLOj6DG2BhOCDuYCv1lUUn+g5hJstDmV616Y75QH+B0Or0b+pj7Gio1MgVzPhaDInkOExsNjnlJ9aRQeb4g/r+fAxuIjt/fkIXBONuaeHWCtrDLkudKuDImbY4+qzeyxBbXaPWNwP8DciQfseGA4ODtZknjDu1QjglVjRFbsiPU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779371225; c=relaxed/simple; bh=C/+huzwQQy8ajj4rVvsB+pzWHwDeRzD/4SFseRN/mrQ=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=rOXm8VLnlOnyJY877ugihwhlVAbDEXKbAbGALVwHh876SodbaXCyvsTxzq2lBchmg09t/RzlYn8Tt/BvU9om1cp2SZZIqFNHm98O/iB4/UNeqxilX0u0kaTigeKrWiDkcGPy49rEjOeLahwQbuqzGzwgeZll7Rzd8NUesTc4aFk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=CVMYSt6b; 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="CVMYSt6b" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C4D221F00A3B; Thu, 21 May 2026 13:47:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1779371223; bh=0uiGPbL5sV7QZfJFJdgMkoYkhlZGTYfT5nxjMkpUgQY=; h=Date:From:To:Cc:Subject:References; b=CVMYSt6bbbT6mXSen8zWSa2qfSg84Qh+w3s4AWGaVvrk3Y+ZVin2iua4QVvlGiz+6 JZuGrwOTTb4CKUAcpTatC6qf+/AgsvlbuNuC9MvL3oHOQvkb70sqXaZp5Dn/v28CgB 4AJTBbgSr0JwayD9hmaMKKQjKSQtPRsoWcKZB3aQpwGBRIzOrYU8u5eIBEHbpN0BqI pYmYhLECzuDU9CQd+kD60ZsFWkQ9p6eZQTeo+NscLAH9FMyOi7YZhkqpGDvdrStW70 5SGXQ7gA96QCr4nkg7V3YbVyLLHRsMU21QewoIyA98QbtAT2/MxmJh4fWNf1UEh0zo /2p3t0IyytBug== Received: from rostedt by gandalf with local (Exim 4.99.2) (envelope-from ) id 1wQ3kD-00000005MQV-0WyH; Thu, 21 May 2026 09:47:25 -0400 Message-ID: <20260521134724.958034353@kernel.org> User-Agent: quilt/0.69 Date: Thu, 21 May 2026 09:47:11 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , stable@vger.kernel.org Subject: [for-linus][PATCH 1/5] ring-buffer: Fix reporting of missed events in iterator References: <20260521134710.628917428@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 From: Steven Rostedt When tracing is active while reading the trace file, if the iterator reading the buffer detects that the writer has passed the iterator head, it will reset and set a "missed events" flag. This flag is passed to the output processing to show the user that events were missed: CPU:4 [LOST EVENTS] The problem is that the flag is reset after it is checked in ring_buffer_iter_dropped(). But the "trace" file iterates over all the CPU ring buffers and it will check if they are dropped when figuring out which buffer to print next. This prematurely clears the missed_events flag if the CPU buffer with the missed events is not the one that is printed next. On the iteration where the CPU buffer with the missed events is printed, the check if it had missed events would return false and the output does not show that events were missed. Do not reset the missed_events flag when checking if there were missed events, but instead clear it when moving the iterator head to the next event. Cc: stable@vger.kernel.org Cc: Mathieu Desnoyers Link: https://patch.msgid.link/20260520220801.4fd09d13@fedora Fixes: c9b7a4a72ff64 ("ring-buffer/tracing: Have iterator acknowledge dropped events") Acked-by: Masami Hiramatsu (Google) Signed-off-by: Steven Rostedt --- kernel/trace/ring_buffer.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 5326924615a4..fcd93d49851e 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -5407,6 +5407,7 @@ static void rb_iter_reset(struct ring_buffer_iter *iter) iter->head_page = cpu_buffer->reader_page; iter->head = cpu_buffer->reader_page->read; iter->next_event = iter->head; + iter->missed_events = 0; iter->cache_reader_page = iter->head_page; iter->cache_read = cpu_buffer->read; @@ -6086,10 +6087,7 @@ ring_buffer_peek(struct trace_buffer *buffer, int cpu, u64 *ts, */ bool ring_buffer_iter_dropped(struct ring_buffer_iter *iter) { - bool ret = iter->missed_events != 0; - - iter->missed_events = 0; - return ret; + return iter->missed_events != 0; } EXPORT_SYMBOL_GPL(ring_buffer_iter_dropped); @@ -6251,7 +6249,7 @@ void ring_buffer_iter_advance(struct ring_buffer_iter *iter) unsigned long flags; raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); - + iter->missed_events = 0; rb_advance_iter(iter); raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); -- 2.53.0