From: Steven Rostedt <rostedt@goodmis.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
"zhangwei(Jovi)" <jovi.zhangwei@huawei.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
Namhyung Kim <namhyung@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
stable <stable@vger.kernel.org>
Subject: Re: [PATCH] uprobes: Use synchronize_rcu() not synchronize_sched()
Date: Fri, 10 Aug 2018 08:48:32 -0400 [thread overview]
Message-ID: <20180810084832.70b9a62a@gandalf.local.home> (raw)
In-Reply-To: <20180810113548.GA3677@redhat.com>
On Fri, 10 Aug 2018 13:35:49 +0200
Oleg Nesterov <oleg@redhat.com> wrote:
> On 08/09, Steven Rostedt wrote:
> >
> > --- a/kernel/trace/trace_uprobe.c
> > +++ b/kernel/trace/trace_uprobe.c
> > @@ -952,7 +952,7 @@ probe_event_disable(struct trace_uprobe *tu, struct trace_event_file *file)
> >
> > list_del_rcu(&link->list);
> > /* synchronize with u{,ret}probe_trace_func */
> > - synchronize_sched();
> > + synchronize_rcu();
>
> Can't we change uprobe_trace_func() and uretprobe_trace_func() to use
> rcu_read_lock_sched() instead? It is more cheap.
Is it? rcu_read_lock_sched() is a preempt_disable(), where
rcu_read_lock() may just be a task counter increment.
>
>
> Hmm. probe_event_enable() does list_del + kfree on failure, this doesn't
> look right... Not only because kfree() can race with list_for_each_entry_rcu(),
> we should not put the 1st link on list until uprobe_buffer_enable().
>
> Does the patch below make sense or I am confused?
I guess the question is, if it isn't enabled, are there any users or
even past users still running. If not, then I think the current code is
OK, as there shouldn't be anything happening to race with it.
-- Steve
>
> Oleg.
>
>
> --- x/kernel/trace/trace_uprobe.c
> +++ x/kernel/trace/trace_uprobe.c
> @@ -896,8 +896,6 @@ probe_event_enable(struct trace_uprobe *
> return -ENOMEM;
>
> link->file = file;
> - list_add_tail_rcu(&link->list, &tu->tp.files);
> -
> tu->tp.flags |= TP_FLAG_TRACE;
> } else {
> if (tu->tp.flags & TP_FLAG_TRACE)
> @@ -909,7 +907,7 @@ probe_event_enable(struct trace_uprobe *
> WARN_ON(!uprobe_filter_is_empty(&tu->filter));
>
> if (enabled)
> - return 0;
> + goto add;
>
> ret = uprobe_buffer_enable();
> if (ret)
> @@ -920,7 +918,8 @@ probe_event_enable(struct trace_uprobe *
> ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
> if (ret)
> goto err_buffer;
> -
> + add:
> + list_add_tail_rcu(&link->list, &tu->tp.files);
> return 0;
>
> err_buffer:
> @@ -928,7 +927,6 @@ probe_event_enable(struct trace_uprobe *
>
> err_flags:
> if (file) {
> - list_del(&link->list);
> kfree(link);
> tu->tp.flags &= ~TP_FLAG_TRACE;
> } else {
next prev parent reply other threads:[~2018-08-10 12:48 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-09 20:05 [PATCH] uprobes: Use synchronize_rcu() not synchronize_sched() Steven Rostedt
2018-08-10 11:35 ` Oleg Nesterov
2018-08-10 11:42 ` Oleg Nesterov
2018-08-10 12:48 ` Steven Rostedt [this message]
2018-08-10 13:36 ` Oleg Nesterov
2018-08-10 13:44 ` Steven Rostedt
2018-08-10 14:06 ` Oleg Nesterov
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=20180810084832.70b9a62a@gandalf.local.home \
--to=rostedt@goodmis.org \
--cc=akpm@linux-foundation.org \
--cc=jovi.zhangwei@huawei.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mhiramat@kernel.org \
--cc=namhyung@kernel.org \
--cc=oleg@redhat.com \
--cc=stable@vger.kernel.org \
/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).