From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D1BD547B436 for ; Thu, 13 Aug 2026 13:12:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.70 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786626727; cv=none; b=q94AVJ9v5DuNz3aGI6gRPNCwmbO6pq3mKtDWF4qffCKlWN0+NdqapG1GwNuTdV01NfwfBzwSspRg32fFm3zDmjlChFlQkHD3H5FBvY0Vo76u6LWVkeQNnIPt+Fe+w+sDhpkPLnKhU332RuyhZ3MyKL0KhpBeExKxWVk65Kxti9Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786626727; c=relaxed/simple; bh=kh+/+F7Yrso+LdumKNDYNclbFEAYJdZStq8JXTkEJVo=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=aMbi+UBBZFQ1YTCQpCSz3uku637gz+cpfmPCKMoamR1clOV1C87N5NZPjhTCh5/2kyiWK7bSEgQH6+faQg4JwbAUtpxPC9cY6n6XtYg+080xV+/rc+prxXKWML4sBpEXZHdan/8QQsJQqWfzlw8TOjDpYnNM+xSapaG5mQspA4Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--vdonnefort.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=JvRJjPXN; arc=none smtp.client-ip=209.85.128.70 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--vdonnefort.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="JvRJjPXN" Received: by mail-wm1-f70.google.com with SMTP id 5b1f17b1804b1-4954b1c6310so7135825e9.0 for ; Thu, 13 Aug 2026 06:12:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1786626724; x=1787231524; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:from:to:cc:subject:date:message-id:reply-to :content-type; bh=hFL43jjwG4Hy2J+x31lo72TgMA0D0unaTk/Ok+c8KgA=; b=JvRJjPXNlbSr1mL2vE00tnB8UnGXh/f0dnPg/jOdhB31UVQd7umfY4ENjGD/x0NZyP trj7tQEm0xt6paGJfTxe1iDj+MgCCHPDBY03Q4KMG/1hmMlHJS/j0mJj5cEaJPfp2fMq ZfOctTz8mfbISGTJ/Urh6qyn2Fmb4POnnSIq7YRcnmsMOeUHxu369P/6NCRGzpM2oZzr rKkT5o4OIhGm4AhkMr6Zpje67Ijh4xmkWBBiOppaXqiQj24YlAaP/9y4IuK4elavtbRy VFavB+YYglXEtobHGfLs8y/KpChcRoBfxIVmWPvct1VsYN0vODgLwats4WkMvmxFPFa4 lw3g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1786626724; x=1787231524; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to:content-type; bh=hFL43jjwG4Hy2J+x31lo72TgMA0D0unaTk/Ok+c8KgA=; b=Ggc0MBuh7b5zvP0sdjTuEgjCEx4aOLOdU/1ssB7LhHYs3WARDUw4HKP6jwZtToZLXu AiSuKSEpMpgchzJiDacfC1sEhPLtMtak1xFqcgWuLJ+H8O5JdmbE3e3y3LSu+yTckd4G YTrkpIOvKZ08G1OxY13Vn+wFHAXb9fIYvLMWeqcyBFSyBq72u9bOVFc2Y2cw7yWghFfz MZVcoOCIvN82pzG8He2Y+gZIunB5iUAO5OWy+nAEEfAxAtgi5OmPvneXNu9X1rMKbVnN 3wm8n7DsvCEVijUtP5GEWDNtcmJva7a8Y4PRnMPYFBsOtiwQXts1W2RJaoEbb40LEUDH n/sQ== X-Forwarded-Encrypted: i=1; AHgh+RrRmwNJ68ovvFqsw0nR5YolqDQdVx8pTlyDWEJ10BIacDYnyLHkLRwrBDVEI4PLoqqVb1OdS+9CpMc7jQ0=@vger.kernel.org X-Gm-Message-State: AOJu0YxTAi01GpeNCS63l5zsBk0Zy1x7qU0ZsoW0MRx0JfH/h/c/LLNb LuKJ9oxVrTWNbWowYm40MR9UCUmnRbUMhWe8373mCNWta0PyFapv85205gDwVsfc8YhLeMgi/vr W/xgnx0rwRJB1x08PMaNK+Q== X-Received: from wmj9.prod.google.com ([2002:a05:600c:249:b0:495:43e1:542c]) (user=vdonnefort job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:840f:b0:493:cc25:85cb with SMTP id 5b1f17b1804b1-4998215ed62mr64783775e9.8.1786626723660; Thu, 13 Aug 2026 06:12:03 -0700 (PDT) Date: Thu, 13 Aug 2026 14:11:49 +0100 In-Reply-To: <20260813131152.3589632-1-vdonnefort@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260813131152.3589632-1-vdonnefort@google.com> X-Mailer: git-send-email 2.55.0.691.gc56d675ccc-goog Message-ID: <20260813131152.3589632-8-vdonnefort@google.com> Subject: [PATCH v5 07/10] ring-buffer: Dynamically calculate max_data_size From: Vincent Donnefort To: rostedt@goodmis.org, mhiramat@kernel.org, linux-trace-kernel@vger.kernel.org Cc: mathieu.desnoyers@efficios.com, kernel-team@android.com, linux-kernel@vger.kernel.org, Vincent Donnefort Content-Type: text/plain; charset="UTF-8" The ring buffer order can be dynamically modified and temporarily disables writing to do so. It is therefore safe to use the updated value to calculate the maximum event size which can be written onto the ring buffer. However, notice it is hardly making any difference for trace_marker because of the TRACE_MARKER_MAX_SIZE limit. For an 8KiB subbuf size, trace_marker can take 4096 characters while it can 'only' take 4054 bytes for smaller subbufs. Fixes: f9b94daa542a ("ring-buffer: Set new size of the ring buffer sub page") Signed-off-by: Vincent Donnefort diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 83292d90599e..d7b3c56e4263 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -598,7 +598,6 @@ struct trace_buffer { struct ring_buffer_meta *meta; unsigned int subbuf_order; - unsigned int max_data_size; }; static __always_inline unsigned int rb_subbuf_size(struct trace_buffer *buffer) @@ -620,6 +619,23 @@ static __always_inline unsigned int rb_subbuf_capacity(struct trace_buffer *buff return rb_subbuf_size(buffer) - BUF_PAGE_HDR_SIZE; } +/** + * rb_subbuf_max_data_size - Get the maximum payload size of a single event + * @buffer: A trace buffer + * + * Return: The maximum data payload size that can be stored in a single event. + */ +static __always_inline unsigned int rb_subbuf_max_data_size(struct trace_buffer *buffer) +{ + struct ring_buffer_event *event; + + /* + * surely rb_subbuf_capacity() is bigger than + * RINGBUF_TYPE_DATA_TYPE_LEN_MAX (see ring_buffer_event_length). + */ + return rb_subbuf_capacity(buffer) - RB_EVNT_HDR_SIZE - sizeof(event->array[0]); +} + /** * rb_subbuf_start - Get the start address of a subbuffer * @buffer: A trace buffer @@ -2773,9 +2789,6 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags, buffer->subbuf_order = order; subbuf_size = (PAGE_SIZE << order); - /* Max payload is buffer page size - header (8bytes) */ - buffer->max_data_size = rb_subbuf_capacity(buffer) - (sizeof(u32) * 2); - buffer->flags = flags; buffer->clock = trace_clock_local; buffer->reader_lock_key = key; @@ -4941,7 +4954,7 @@ rb_reserve_next_event(struct trace_buffer *buffer, if (ring_buffer_time_stamp_abs(cpu_buffer->buffer)) { add_ts_default = RB_ADD_STAMP_ABSOLUTE; info.length += RB_LEN_TIME_EXTEND; - if (info.length > cpu_buffer->buffer->max_data_size) + if (info.length > rb_subbuf_max_data_size(cpu_buffer->buffer)) goto out_fail; } else { add_ts_default = RB_ADD_STAMP_NONE; @@ -5016,7 +5029,7 @@ ring_buffer_lock_reserve(struct trace_buffer *buffer, unsigned long length) if (unlikely(atomic_read(&cpu_buffer->record_disabled))) goto out; - if (unlikely(length > buffer->max_data_size)) + if (unlikely(length > rb_subbuf_max_data_size(buffer))) goto out; if (unlikely(trace_recursive_lock(cpu_buffer))) @@ -5163,7 +5176,7 @@ int ring_buffer_write(struct trace_buffer *buffer, if (atomic_read(&cpu_buffer->record_disabled)) return -EBUSY; - if (length > buffer->max_data_size) + if (length > rb_subbuf_max_data_size(buffer)) return -EBUSY; if (unlikely(trace_recursive_lock(cpu_buffer))) @@ -6522,8 +6535,9 @@ unsigned long ring_buffer_max_event_size(struct trace_buffer *buffer) { /* If abs timestamp is requested, events have a timestamp too */ if (ring_buffer_time_stamp_abs(buffer)) - return buffer->max_data_size - RB_LEN_TIME_EXTEND; - return buffer->max_data_size; + return rb_subbuf_max_data_size(buffer) - RB_LEN_TIME_EXTEND; + + return rb_subbuf_max_data_size(buffer); } EXPORT_SYMBOL_GPL(ring_buffer_max_event_size); @@ -7982,7 +7996,7 @@ int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu) * missed events, then record it there. */ commit = rb_page_size(reader); - if (rb_subbuf_capacity(buffer) - commit >= sizeof(missed_events)) { + if (rb_page_capacity(reader) - commit >= sizeof(missed_events)) { memcpy(&dpage->data[commit], &missed_events, sizeof(missed_events)); local_add(RB_MISSED_STORED, &dpage->commit); -- 2.55.0.691.gc56d675ccc-goog