From: Peter Zijlstra <peterz@infradead.org>
To: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org, vince@deater.net,
eranian@google.com, Arnaldo Carvalho de Melo <acme@infradead.org>,
Jiri Olsa <jolsa@kernel.org>,
alexei.starovoitov@gmail.com
Subject: Re: [PATCH v2] perf: Synchronously cleanup child events
Date: Tue, 19 Jan 2016 21:05:58 +0100 [thread overview]
Message-ID: <20160119200558.GC6357@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <1453216354-9282-1-git-send-email-alexander.shishkin@linux.intel.com>
On Tue, Jan 19, 2016 at 05:12:34PM +0200, Alexander Shishkin wrote:
> +static void __put_event(struct perf_event *event)
> {
> struct perf_event_context *ctx;
>
> if (!is_kernel_event(event))
> perf_remove_from_owner(event);
>
> +int perf_event_release_kernel(struct perf_event *event)
> {
> + struct perf_event *child, *tmp;
> + LIST_HEAD(child_list);
>
> + if (!is_kernel_event(event))
> + perf_remove_from_owner(event);
>
> + event->owner = NULL;
>
> +retry:
<snip>
> + /*
> + * If this is the last reference, we're done here, otherwise
> + * we must have raced with inherit_event(), in which case, repeat
> + */
> + if (!put_event_last(event))
> + goto retry;
>
> + return 0;
> +}
So I think there's a number of problems still :-(
I all starts with having two perf_remove_from_owner() calls (as I
mentioned on IRC), this doesn't make sense.
I think the moment you close the file and userspace looses control over
it, we should drop the owner bit, which is exactly the one
remove_from_owner in perf_release().
If, for some magical reason, the event lives on after that (and we'll
get to that), it should live on owner-less.
Now, assume someone has such a magical reference, then our
put_event_last() goto again loop will never terminate, this seems like a
bad thing.
The most obvious place that generates such magical references would be
the bpf arraymap doing perf_event_get() on things. There are a few other
places that take temp references (perf_mmap_close), but those are
'short' lived and while ugly will not cause massive grief. The BPF one
OTOH is a real problem here.
And looking at the BPF stuff, that code seems to assume
perf_event_kernel_release() := put_event(), so this patch breaks that
too.
Alexei, is there a reason the arraymap stuff needs a perf event ref as
opposed to a file ref? I'm forever a little confused on how perf<->bpf
works.
next prev parent reply other threads:[~2016-01-19 20:06 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-15 11:22 [PATCH] perf: Cleanup user's child events Alexander Shishkin
2016-01-15 12:54 ` Peter Zijlstra
2016-01-15 13:05 ` Alexander Shishkin
2016-01-15 13:09 ` Peter Zijlstra
2016-01-15 14:07 ` [PATCH] perf: Synchronously cleanup " Alexander Shishkin
2016-01-15 17:57 ` Peter Zijlstra
2016-01-18 12:07 ` Alexander Shishkin
2016-01-18 12:37 ` Alexander Shishkin
2016-01-18 14:44 ` Peter Zijlstra
2016-01-19 15:12 ` [PATCH v2] " Alexander Shishkin
2016-01-19 20:05 ` Peter Zijlstra [this message]
2016-01-19 21:58 ` Alexei Starovoitov
2016-01-20 8:32 ` Peter Zijlstra
2016-01-21 4:55 ` Alexei Starovoitov
2016-01-20 7:04 ` Alexander Shishkin
2016-01-20 8:03 ` Peter Zijlstra
2016-01-22 11:35 ` Alexander Shishkin
2016-01-22 12:12 ` Peter Zijlstra
2016-01-22 12:38 ` Peter Zijlstra
2016-01-22 19:44 ` Alexei Starovoitov
2016-01-25 11:48 ` Peter Zijlstra
2016-01-25 14:54 ` Peter Zijlstra
2016-01-25 21:04 ` Peter Zijlstra
2016-01-26 4:59 ` Alexei Starovoitov
2016-01-26 16:16 ` Peter Zijlstra
2016-01-26 17:24 ` Peter Zijlstra
2016-01-26 23:31 ` Alexei Starovoitov
2016-01-27 9:58 ` Peter Zijlstra
2016-01-27 17:52 ` Alexei Starovoitov
2016-01-29 11:28 ` [tip:perf/urgent] perf/bpf: Convert perf_event_array to use struct file tip-bot for Alexei Starovoitov
2016-01-29 20:01 ` Alexei Starovoitov
2016-01-19 20:07 ` [PATCH v2] perf: Synchronously cleanup child events Peter Zijlstra
2016-01-19 7:45 ` [PATCH] " Ingo Molnar
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20160119200558.GC6357@twins.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=acme@infradead.org \
--cc=alexander.shishkin@linux.intel.com \
--cc=alexei.starovoitov@gmail.com \
--cc=eranian@google.com \
--cc=jolsa@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=vince@deater.net \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).