From nobody Fri Dec 19 14:43:50 2025 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 6EFD11C6BE; Tue, 20 May 2025 06:13:42 +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=1747721622; cv=none; b=Hd+FQd7P4Fr7k8g0wnIpeJFKjsUP+J/E2m3dstBNUSCHpyAbCwNhBNnLxygq3VtWIVW6jXt9t9vqQxow8veZ/O7G22UV8ohiQrBGT6fBUKOjki88+Hpdq6ZSw/x5YxwnmJbGHqDnHz4Nm21vzJ2MQD9HD8K6LmZFo9rxYSyQUys= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747721622; c=relaxed/simple; bh=qv24cgaIowjqbztnCwTh6HyqJ2LT0oEfi9MxLUaIjUA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=tbrk9lpp6lf1qLuGFJDNbXFz64OO76WhYD9yXINSkiZ6RVi/G4P1gfTBfSsYehNCRlTvAxDNZwxKeMphiQW9MbY+BikSQfREQqJjYfIHhnoVNLYp94d2U4D8n+H5vSLbJ8DIahrx4OK+ALBjZ5aqHB2l2fqO1PaGS6pLD5t4mJA= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=iKF/m41X; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="iKF/m41X" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 12781C4CEE9; Tue, 20 May 2025 06:13:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1747721621; bh=qv24cgaIowjqbztnCwTh6HyqJ2LT0oEfi9MxLUaIjUA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=iKF/m41XkYWF6WjZcP3accTMgSHgfJaIOf79+sw65RQDHU4Oi04a62Z6UzaBkksaa BueBeSZICIWvvVfEGVFAA939xchaWIc7QWcNJTLv1f6S86a6rb0dt5VAax2S71spZQ B3WNE8S/+RMbJXIE3TQAahfXkeo/R5nOkf99jFTcUaCJTUdguphKMTkj5pnpp+KM9X JvPpOgJ6dBNZ1DeXYScbLsUO+uVKFHrJSeSGIcwJAVSevOpGgvkYy/6nuwxVTrgA35 Z+LROySr56xZTaZkL5UgAUtyxeScx4VgyuOFHpgxXj42ienZi6owLiTFlXnooyoxdP YHSaAXK/ztUIA== From: "Masami Hiramatsu (Google)" To: Steven Rostedt Cc: Masami Hiramatsu , Mathieu Desnoyers , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: [PATCH] tracing: Reset last-boot buffers when reading out all cpu buffers Date: Tue, 20 May 2025 15:13:38 +0900 Message-ID: <174772161786.1341812.8912662133740822008.stgit@mhiramat.tok.corp.google.com> X-Mailer: git-send-email 2.49.0.1143.g0be31eac6b-goog In-Reply-To: <174730775661.3893490.10420015749079085314.stgit@mhiramat.tok.corp.google.com> References: <174730775661.3893490.10420015749079085314.stgit@mhiramat.tok.corp.google.com> User-Agent: StGit/0.19 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" Content-Transfer-Encoding: quoted-printable 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, it does not reset because there will be the data in reader page. Suggested-by: Steven Rostedt Signed-off-by: Masami Hiramatsu (Google) --- kernel/trace/trace.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 2c1764ed87b0..433671d3aa43 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -6677,6 +6677,22 @@ static int tracing_wait_pipe(struct file *filp) return 1; } =20 +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. */ @@ -6708,6 +6724,9 @@ tracing_read_pipe(struct file *filp, char __user *ubu= f, } =20 waitagain: + if (update_last_data_if_empty(iter->tr)) + return 0; + sret =3D tracing_wait_pipe(filp); if (sret <=3D 0) return sret; @@ -8286,6 +8305,9 @@ tracing_buffers_read(struct file *filp, char __user *= ubuf, =20 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;