Messages in this thread | | | Date | Mon, 21 Aug 2023 11:19:54 +0900 | From | Masami Hiramatsu (Google) <> | Subject | Re: [PATCH v2] tracing: Introduce pipe_cpumask to avoid race on trace_pipes |
| |
On Sat, 19 Aug 2023 10:42:57 +0900 Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:
> On Fri, 18 Aug 2023 11:53:22 -0400 > Steven Rostedt <rostedt@goodmis.org> wrote: > > > On Fri, 18 Aug 2023 23:23:01 +0900 > > Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote: > > > > > It uses trace_pipe_raw. I guess if splice(from trace_pipe_raw to virtio-serial) > > > returns -1 and errno == EAGAIN, the trace data will be lost? > > > > It shouldn't. If it does, then there's likely a bug. The code will block > > and if an interrupt comes in it will return immediately without reading > > from the buffer. > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/trace/trace.c#n8262 > > > > I don't see where it would return -EINTR and consume data, but I may be > > missing something. > > Hmm, I suspect the case if the spilice_to_pipe() returns -EAGAIN. > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/trace/trace.c#n8491 > > It seems not handling such case. > > Anyway, I also think something wrong in virtio-serial (or misusing?), since > it can not read anything from the host sometimes. I just setup the virtio-trace > with below patch (ignore EAGAIN). > > > From 92242480285448360c9390a743ea7b3751bb3e61 Mon Sep 17 00:00:00 2001 > From: "Masami Hiramatsu (Google)" <mhiramat@kernel.org> > Date: Thu, 17 Aug 2023 14:08:40 +0900 > Subject: [PATCH 1/3] tools/virtio-trace: Ignore EAGAIN error on splice() > > splice() can return EAGAIN error instead of returning 0 size read. > In that case, wait a while and try to call splice() again. > > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> > --- > tools/virtio/virtio-trace/trace-agent-rw.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/tools/virtio/virtio-trace/trace-agent-rw.c b/tools/virtio/virtio-trace/trace-agent-rw.c > index ddfe7875eb16..e8a4c4f0c499 100644 > --- a/tools/virtio/virtio-trace/trace-agent-rw.c > +++ b/tools/virtio/virtio-trace/trace-agent-rw.c > @@ -8,6 +8,7 @@ > */ > > #define _GNU_SOURCE > +#include <errno.h> > #include <fcntl.h> > #include <stdio.h> > #include <stdlib.h> > @@ -127,10 +128,10 @@ static void *rw_thread_main(void *thread_info) > rlen = splice(ts->in_fd, NULL, ts->read_pipe, NULL, > ts->pipe_size, SPLICE_F_MOVE | SPLICE_F_MORE); > > - if (rlen < 0) { > - pr_err("Splice_read in rw-thread(%d)\n", ts->cpu_num); > + if (rlen < 0 && errno != EAGAIN) { > + pr_err("Splice_read error (%d) in rw-thread(%d)\n", errno, ts->cpu_num); > goto error; > - } else if (rlen == 0) { > + } else if (rlen == 0 || errno == EAGAIN) {
Ah, this caused a drop. errno can be EAGAIN even if rlen > 0. I've fixed this and that works. BTW, I think this virtio-trace would be better to move under tools/tracing because it is a tracing tool.
Thanks,
> /* > * If trace data do not exist or are unreadable not > * for exceeding the page size, splice_read returns > -- > 2.34.1 > > > -- > Masami Hiramatsu (Google) <mhiramat@kernel.org>
-- Masami Hiramatsu (Google) <mhiramat@kernel.org>
| |