From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 2BAA92222A8 for ; Wed, 28 May 2025 22:26:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748471189; cv=none; b=ibJevlJw55HtPC9lsANFLTF2rLAolPng1oa2wzzxchjEhJkKcpZf5c9K3vhOa/TTnbaEJNXb3Tw/nctE+5ckg4Cg1F85IgFZsTcXi2sE4ioS0RWoFQXPwbUv6e/u3/Qcu67pEvlsElA90PIYjIxKFYY9dT73r7UBkS3B/BVwBzQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748471189; c=relaxed/simple; bh=x2ZdQ+E55F671MXAJwMZKQca4oYCPqwh6Smyb4/yja4=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=hPod/mOtuQFX3lV7vHyJxHF1IZgNrDrG3HmPcA4h0ZIaBr3ARd//sQUJWORwJ/hsbAAiAu2XJYmoDHMm8B6D+G+dvEoFHPFXyMWDv9a4yHeohQa5DixeSF7pgWjBQga2H9P8ULHIyYlaJtO65XiNZa03aVenvmp9IV4tdSA4I+k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id C449FC4CEEE; Wed, 28 May 2025 22:26:28 +0000 (UTC) Received: from rostedt by gandalf with local (Exim 4.98.2) (envelope-from ) id 1uKPFC-0000000AozU-0HV5; Wed, 28 May 2025 18:27:30 -0400 Message-ID: <20250528222729.919034654@goodmis.org> User-Agent: quilt/0.68 Date: Wed, 28 May 2025 18:27:08 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton Subject: [for-next][PATCH 04/10] tracing: Reset last-boot buffers when reading out all cpu buffers References: <20250528222704.623477429@goodmis.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 From: "Masami Hiramatsu (Google)" Reset the last-boot ring buffers when read() reads out all cpu buffers through trace_pipe/trace_pipe_raw. This prevents ftrace to unwind ring buffer read pointer next boot. Note that this resets only when all per-cpu buffers are empty, and read via read(2) syscall. For example, if you read only one of the per-cpu trace_pipe, it does not reset it. Also, reading buffer by splice(2) syscall does not reset because some data in the reader (the last) page. Cc: Mathieu Desnoyers Link: https://lore.kernel.org/174792929202.496143.8184644221859580999.stgit@mhiramat.tok.corp.google.com Suggested-by: Steven Rostedt Signed-off-by: Masami Hiramatsu (Google) Signed-off-by: Steven Rostedt (Google) --- kernel/trace/trace.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 73d75cdb7e5b..ecb774cc01ab 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -6610,6 +6610,22 @@ static int tracing_wait_pipe(struct file *filp) return 1; } +static bool update_last_data_if_empty(struct trace_array *tr) +{ + if (!(tr->flags & TRACE_ARRAY_FL_LAST_BOOT)) + return false; + + if (!ring_buffer_empty(tr->array_buffer.buffer)) + return false; + + /* + * If the buffer contains the last boot data and all per-cpu + * buffers are empty, reset it from the kernel side. + */ + update_last_data(tr); + return true; +} + /* * Consumer reader. */ @@ -6641,6 +6657,9 @@ tracing_read_pipe(struct file *filp, char __user *ubuf, } waitagain: + if (update_last_data_if_empty(iter->tr)) + return 0; + sret = tracing_wait_pipe(filp); if (sret <= 0) return sret; @@ -8167,6 +8186,9 @@ tracing_buffers_read(struct file *filp, char __user *ubuf, if (ret < 0) { if (trace_empty(iter) && !iter->closed) { + if (update_last_data_if_empty(iter->tr)) + return 0; + if ((filp->f_flags & O_NONBLOCK)) return -EAGAIN; -- 2.47.2