From patchwork Sat Feb 4 19:33:45 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Shiju Jose X-Patchwork-Id: 13128871 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 27DFAC61DA4 for ; Sat, 4 Feb 2023 19:34:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230297AbjBDTd7 (ORCPT ); Sat, 4 Feb 2023 14:33:59 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40998 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229746AbjBDTd6 (ORCPT ); Sat, 4 Feb 2023 14:33:58 -0500 Received: from frasgout.his.huawei.com (frasgout.his.huawei.com [185.176.79.56]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BCD2C2B090; Sat, 4 Feb 2023 11:33:53 -0800 (PST) Received: from lhrpeml500006.china.huawei.com (unknown [172.18.147.207]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4P8Mzq6hCkz67K2n; Sun, 5 Feb 2023 03:29:59 +0800 (CST) Received: from P_UKIT01-A7bmah.china.huawei.com (10.195.244.18) by lhrpeml500006.china.huawei.com (7.191.161.198) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.17; Sat, 4 Feb 2023 19:33:50 +0000 From: To: , CC: , , , , , , , Subject: [RFC PATCH V2 1/1] rasdaemon: Fix poll() on per_cpu trace_pipe_raw blocks indefinitely Date: Sat, 4 Feb 2023 19:33:45 +0000 Message-ID: <20230204193345.842-1-shiju.jose@huawei.com> X-Mailer: git-send-email 2.26.0.windows.1 MIME-Version: 1.0 X-Originating-IP: [10.195.244.18] X-ClientProxiedBy: lhrpeml500004.china.huawei.com (7.191.163.9) To lhrpeml500006.china.huawei.com (7.191.161.198) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-trace-kernel@vger.kernel.org From: Shiju Jose The error events are not received in the rasdaemon since kernel 6.1-rc6. This issue is firstly detected and reported, when testing the CXL error events in the rasdaemon. Debugging showed, poll() on trace_pipe_raw in the ras-events.c do not return and this issue is seen after the commit 42fb0a1e84ff525ebe560e2baf9451ab69127e2b ("tracing/ring-buffer: Have polling block on watermark"). This also verified using a test application for poll() and select() on trace_pipe_raw. There is also a bug reported on this issue, https://lore.kernel.org/all/31eb3b12-3350-90a4-a0d9-d1494db7cf74@oracle.com/ This issue occurs for the per_cpu case, which calls the ring_buffer_poll_wait(), in kernel/trace/ring_buffer.c, with the buffer_percent > 0 and then wait until the percentage of pages are available.The default value set for the buffer_percent is 50 in the kernel/trace/trace.c. However poll() does not return even met the percentage of pages condition. As a fix, rasdaemon set buffer_percent as 0 through the /sys/kernel/debug/tracing/instances/rasdaemon/buffer_percent, then the task will wake up as soon as data is added to any of the specific cpu buffer and poll() on per_cpu/cpuX/trace_pipe_raw does not block indefinitely. Dependency on the kernel RFC patch tracing: Fix poll() and select() do not work on per_cpu trace_pipe and trace_pipe_raw Signed-off-by: Shiju Jose Changes: RFC V1 -> RFC V2 1. Rename the patch header subject. 2. Changes for the backward compatability to the old kernels. Reported-by: Harshit Mogalapalli --- ras-events.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/ras-events.c b/ras-events.c index 3691311..e505a0e 100644 --- a/ras-events.c +++ b/ras-events.c @@ -383,6 +383,8 @@ static int read_ras_event_all_cpus(struct pthread_data *pdata, int warnonce[n_cpus]; char pipe_raw[PATH_MAX]; int legacy_kernel = 0; + int fd; + char buf[10]; #if 0 int need_sleep = 0; #endif @@ -402,6 +404,26 @@ static int read_ras_event_all_cpus(struct pthread_data *pdata, return -ENOMEM; } + /* Fix for poll() on the per_cpu trace_pipe and trace_pipe_raw blocks + * indefinitely with the default buffer_percent in the kernel trace system, + * which is introduced by the following change in the kernel. + * https://lore.kernel.org/all/20221020231427.41be3f26@gandalf.local.home/T/#u. + * Set buffer_percent to 0 so that poll() will return immediately + * when the trace data is available in the ras per_cpu trace pipe_raw + */ + fd = open_trace(pdata[0].ras, "buffer_percent", O_WRONLY); + if (fd >= 0) { + /* For the backward compatabilty to the old kernel, do not return + * if fail to set the buffer_percent. + */ + snprintf(buf, sizeof(buf), "0"); + size = write(fd, buf, strlen(buf)); + if (size <= 0) + log(TERM, LOG_WARNING, "can't write to buffer_percent\n"); + close(fd); + } else + log(TERM, LOG_WARNING, "Can't open buffer_percent\n"); + for (i = 0; i < (n_cpus + 1); i++) fds[i].fd = -1;