From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752787AbaF0Gw4 (ORCPT ); Fri, 27 Jun 2014 02:52:56 -0400 Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:60168 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751598AbaF0Gwz (ORCPT ); Fri, 27 Jun 2014 02:52:55 -0400 Date: Thu, 26 Jun 2014 23:52:45 -0700 From: Martin Lau To: Steven Rostedt CC: , Subject: Re: [PATCH] ring-buffer: Fix polling on trace_pipe Message-ID: <20140627065243.GA2826@devbig242.prn2.facebook.com> References: <20140610060637.GA14045@devbig242.prn2.facebook.com> <20140610114915.5fe24841@gandalf.local.home> <20140611055814.GA30265@devbig242.prn2.facebook.com> <20140626183445.GA2663@devbig242.prn2.facebook.com> <20140626205327.5b526302@gandalf.local.home> MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="45Z9DzgjV8m4Oswq" Content-Disposition: inline In-Reply-To: <20140626205327.5b526302@gandalf.local.home> User-Agent: Mutt/1.5.20 (2009-12-10) X-Originating-IP: [192.168.57.29] X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:5.12.52,1.0.14,0.0.0000 definitions=2014-06-27_03:2014-06-26,2014-06-27,1970-01-01 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 kscore.is_bulkscore=0 kscore.compositescore=0 circleOfTrustscore=22.6900859407804 compositescore=0.997695897463551 urlsuspect_oldscore=0.997695897463551 suspectscore=0 recipient_domain_to_sender_totalscore=0 phishscore=0 bulkscore=0 kscore.is_spamscore=0 recipient_to_sender_totalscore=0 recipient_domain_to_sender_domain_totalscore=64355 rbsscore=0.997695897463551 spamscore=0 recipient_to_sender_domain_totalscore=6 urlsuspectscore=0.9 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=7.0.1-1402240000 definitions=main-1406270086 X-FB-Internal: deliver Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --45Z9DzgjV8m4Oswq Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline Hi Steve, I retried the test program (with the kernel patch). It does block from time to time. I spotted the ee.events is not set to EPOLLIN before calling epll_ctl(eft, EPOLL_CTL_ADD,...). I fixed it and ran the test in a bash-loop. I have the kafai-2 version attached (with some more logging in case if it still blocks). Can you retry? Thanks, Martin On Thu, Jun 26, 2014 at 08:53:27PM -0400, Steven Rostedt wrote: > On Thu, 26 Jun 2014 11:34:46 -0700 > Martin Lau wrote: > > > Hi Steve, > > > > Can the modified test program reproduce the problem in your test setup? > > Ah sorry, got distracted by other work. > > OK, I just tried it out, and here's my results: > > I ran you code with my current kernel and this is what I got: > > # ./ftrace-test-epoll-kafai > <...>-3183 [002] ...1 81.777891: tracing_mark_write: > some data 3183: waitting for more data...... > 3184: written more data > > And it just hung there. > > > Then I applied your patch, compiled and booted it, and ran the test > again, and I got this: > > # ./ftrace-test-epoll-kafai > > It just hung there. No forward progress. > > I don't think that was the result you intended. > > -- Steve > > --45Z9DzgjV8m4Oswq Content-Type: text/plain; charset="us-ascii" Content-Disposition: attachment; filename="ftrace-test-epoll-kafai-2.c" #include #include #include #include #include #include #include #include #include static const char * debugfs_list[] = { "/debug/tracing", "/sys/kernel/debug/tracing", "/d/tracing", NULL, }; static const char *debugfs; static int markfd; static int trace_pipe_fd; static void alog(const char *name, int ret) { printf("%d: %s: %d\n", getpid(), name, ret); } static const char *find_debugfs(void) { struct stat st; int i; int r; for (i = 0; debugfs_list[i]; i++) { r = stat(debugfs_list[i], &st); if (r < 0) continue; if (S_ISDIR(st.st_mode)) return debugfs_list[i]; } return NULL; } static char * make_path(const char *file) { char *path; int size; size = strlen(debugfs) + strlen(file) + 2; path = malloc(size); if (!path) { perror("malloc"); exit(-1); } sprintf(path, "%s/%s", debugfs, file); return path; } static void mark_write(const char *str) { int ret; ret = write(markfd, str, strlen(str)); alog("write(markfd)", ret); } static void read_trace_pipe(void) { char buf[1024]; int r; while ((r = read(trace_pipe_fd, buf, 1024)) > 0) printf("%.*s", r, buf); } int main (int argc, char **argv) { struct epoll_event ee; char *marker; char *pipe; int efd; int ret; pid_t dwrt_pid; debugfs = find_debugfs(); if (!debugfs) { fprintf(stderr, "Could not find debugfs\n"); exit(-1); } marker = make_path("trace_marker"); pipe = make_path("trace_pipe"); markfd = open(marker, O_WRONLY); if (markfd < 0) { perror("marker"); exit(-1); } trace_pipe_fd = open(pipe, O_RDONLY|O_NONBLOCK); if (trace_pipe_fd < 0) { perror("trace_pipe"); exit(-1); } efd = epoll_create(1); if (efd < 0) { perror("epoll_create"); exit(-1); } mark_write("some data"); memset(&ee, 0, sizeof(ee)); ee.events = EPOLLIN; ret = epoll_ctl(efd, EPOLL_CTL_ADD, trace_pipe_fd, &ee); if (ret < 0) { perror("epoll_ctl"); exit(-1); } alog("waiting data......", 0); ret = epoll_wait(efd, &ee, 1, -1); alog("epoll_wait()", ret); read_trace_pipe(); dwrt_pid = fork(); assert(dwrt_pid != -1); if (dwrt_pid == 0) { sleep(10); mark_write("more data"); } else { alog("waiting form more data......", 0); ret = epoll_wait(efd, &ee, 1, -1); alog("epoll_wait()", ret); read_trace_pipe(); wait(NULL); } return 0; } --45Z9DzgjV8m4Oswq--