linux-kernel - Re: [BUG] perf stat: hangs with -p and process completes

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 16 Oct 2018 13:03:41 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Stephane Eranian <eranian@...gle.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Subject: Re: [BUG] perf stat: hangs with -p and process completes

On Fri, Oct 12, 2018 at 02:26:09PM -0700, Stephane Eranian wrote:
> Hi,
> 
> I am running into a perf stat issue with the -p option which allows you
> to attach to a running process. If that process happens to terminate
> while under monitoring
> perf hangs in there and never terminates. The proper behavior would be to stop.
> I can see the issue in that the attached process is not a child, so
> wait() would not work.
> 
> To reproduce:
>   $ sleep 10 &
>   $ perf stat -p $!
> 
> doing the same with perf record works, so there is a solution to this problem.

yea, we don't poll for the event state change in perf stat,
but we do that in perf record.. also because the perf poll
code in kernel is originaly meant for tracking the ring
buffer state

maybe we could return EPOLLIN for alive events without ring
buffer.. like below (totaly untested) and add polling for 
event state into perf stat 

cc-ing perf folks

jirka


---
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 5a97f34bc14c..b9ee7e7803bf 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4865,12 +4865,12 @@ static __poll_t perf_poll(struct file *file, poll_table *wait)
 {
 	struct perf_event *event = file->private_data;
 	struct ring_buffer *rb;
-	__poll_t events = EPOLLHUP;
+	__poll_t events = EPOLLIN;
 
 	poll_wait(file, &event->waitq, wait);
 
 	if (is_event_hup(event))
-		return events;
+		return EPOLLHUP;
 
 	/*
 	 * Pin the event->rb by taking event->mmap_mutex; otherwise