From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f71.google.com (mail-wm1-f71.google.com [209.85.128.71]) (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 2C42141D4FE for ; Thu, 6 Aug 2026 21:13:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.71 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786050804; cv=none; b=BE+/nvczJOi+CfoYXIuoghCavrhfnlpddrHBf9Al6CbiULjq4TGrkSQEeKa4afzcr/Vb5FPDtiZGG/H6yxGT/tk/ug7NHYocVC/FywPMHgVhyZqX+JIQmHCg2OxCX+1zxb/iEc8BK6TEJySouhRkVLW7BxGAiHrVu5k3nHJUqZk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786050804; c=relaxed/simple; bh=CNQvFhVdRoGryLzJvLKX3hSTsH+qre2RJpUcVf9nXh4=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=P/13r1uuHlq9L+RKrzCibee8+82HdA9BME/4VAnH6DImCVu/B0eGDSr7UMQbBRROOT4I9rnyNYTSUrapCWrYrH9HzOr8hTLx+GrVCzM1vTJL78JFIDDGL3nPJZxHjQphhFVBDadc9bdaVrjDpAWLcXYnv2XMSIhyec/+7hLaCtY= 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=IccDDM99; arc=none smtp.client-ip=209.85.128.71 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="IccDDM99" Received: by mail-wm1-f71.google.com with SMTP id 5b1f17b1804b1-4994d67d0e3so18763695e9.2 for ; Thu, 06 Aug 2026 14:13:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1786050801; x=1786655601; 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=cXf5OkyQb5t84Kc/wGzH1+QneGiHelNLSJRdaS24HXA=; b=IccDDM99e7E1RAIfTfbyL7r97zFtwKJF28/mG7tHKgjjMHrRyMDI9HZBi5BRqIaI9F kYU65IBfh8JyuES9n6ZSUn5D2oS7rzmYSR3wqaeka3hULvuQ/Um0zXKOlWzbbF3VrdkK s8Bj18bqiRnht2URu9HtedVOFcMlg/e88Z9UYM3y0UE2wtxMMSpnbetMVawu3HxszkHy sVM4eYTLNEZJwCz1BOm/9z5fcga43Ximpm/AQ0TOvZQ/knZh+gjUGbN6vs3c/bfDfuO5 GpMDbA8+xuC/wrga7YYZrswgmqg9vU+dM2Jy2h9egfRJmQd40Wg3rXR3T9nAknF/Ge9Y ZyhQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1786050801; x=1786655601; 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=cXf5OkyQb5t84Kc/wGzH1+QneGiHelNLSJRdaS24HXA=; b=TklOMCwdfg6VOCDd9zMghLoV/NiOvw1dUataWLTyICYWSUK6sYbMxpWqmkZKAb6UDV JMCZuvuCSjBK90LIYtq0ws12gV4Lko432kXy9m664SXVZ72C0fxtBFtbMjl8vuv1L5V9 sDxmNyNI5CFPTkruLjYtFJk7MPj1HaJmMx/kR1/VJdyNbPIG2dCVkVgOHTi4gtkP3jr6 iRdi4b5B//AfhGx0KHMxEhksEzdir8IhPnutGlYV2mHngiW9PJg0DUBGRZwTZtQXOGiM UAMCmFcJ32o37qkI/r1War4qgQCccbTYx+T1HCIZc6DjTnr0JdMIt5nzcYoxl5LtFN0p qn2Q== X-Forwarded-Encrypted: i=1; AHgh+RquVGa5k/kQrS8BTIFANrWXtdaTWb7mGObRXX1WZa7hrdM2+HZ0P3mKyyJ4Ubb0fKqTTimhqn9is8dAgQs=@vger.kernel.org X-Gm-Message-State: AOJu0Yx0ItAlqkVwSznPNd0GgOenO5sXtTMmhxnLADbSDlONnHFpS1cZ umaKR1cKwfzrH5+Dthxclmtnn8mfsAhfjwX52cUfw3GOuCJ6DHOxiYL37gYlNk4dwdn9w/m878E QEg9EPAnK2Nckav6VpvEGGw== X-Received: from wmbb14.prod.google.com ([2002:a05:600c:588e:b0:495:4a25:69f7]) (user=vdonnefort job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:4f4a:b0:499:51f0:a9b2 with SMTP id 5b1f17b1804b1-49959e0179bmr50513235e9.1.1786050801122; Thu, 06 Aug 2026 14:13:21 -0700 (PDT) Date: Thu, 6 Aug 2026 22:13:05 +0100 In-Reply-To: <20260806211306.3704194-1-vdonnefort@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260806211306.3704194-1-vdonnefort@google.com> X-Mailer: git-send-email 2.55.0.654.g21b8a5bc05-goog Message-ID: <20260806211306.3704194-6-vdonnefort@google.com> Subject: [PATCH 5/6] 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 3531005aab43..d2480ccc81b8 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -587,7 +587,6 @@ struct trace_buffer { struct ring_buffer_meta *meta; unsigned int subbuf_order; - unsigned int max_data_size; }; static inline unsigned int rb_subbuf_size(struct trace_buffer *buffer) @@ -600,6 +599,17 @@ static inline unsigned int rb_subbuf_capacity(struct trace_buffer *buffer) return rb_subbuf_size(buffer) - BUF_PAGE_HDR_SIZE; } +static inline unsigned int rb_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]); +} + static inline unsigned int rb_page_capacity(struct buffer_page *bpage) { return (PAGE_SIZE << bpage->order) - BUF_PAGE_HDR_SIZE; @@ -2745,9 +2755,6 @@ 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; @@ -4914,7 +4921,7 @@ 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_max_data_size(cpu_buffer->buffer)) goto out_fail; } else { add_ts_default = RB_ADD_STAMP_NONE; @@ -4989,7 +4996,7 @@ 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_max_data_size(buffer))) goto out; if (unlikely(trace_recursive_lock(cpu_buffer))) @@ -5136,7 +5143,7 @@ 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_max_data_size(buffer)) return -EBUSY; if (unlikely(trace_recursive_lock(cpu_buffer))) @@ -6495,8 +6502,9 @@ 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_max_data_size(buffer) - RB_LEN_TIME_EXTEND; + + return rb_max_data_size(buffer); } EXPORT_SYMBOL_GPL(ring_buffer_max_event_size); -- 2.55.0.654.g21b8a5bc05-goog