linux-kernel - Re: probe_event_disable()->synchronize

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Message-ID: <20140703154131.GA5610@redhat.com>
Date:	Thu, 3 Jul 2014 17:41:31 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Namhyung Kim <namhyung@...il.com>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Tom Zanussi <tom.zanussi@...ux.intel.com>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	linux-kernel@...r.kernel.org
Subject: Re: probe_event_disable()->synchronize_sched()

On 07/03, Namhyung Kim wrote:
>
> On Tue, 1 Jul 2014 21:31:47 +0200, Oleg Nesterov wrote:
> >
> > And. I am puzzled by probe_event_disable()->synchronize_sched(). Why
> > do we need it? I mean, why we can't use call_rcu() ? The comment says
> > "synchronize with u{,ret}probe_trace_func" but it doesn't explain _why_
> > do we need to sync.
>
> It looks like the code was copied from trace_kprobe.c file.  But IIUC,
> unlike kprobes, uprobe events are always called in a process context.
>
> Also u{,ret}probe_trace_func() call handlers under rcu_read_lock() not
> rcu_read_lock_sched() so I guess the synchronize_sched() can go.

Heh ;) I didn't even notice that "synchronize" and "lock" do not match.
So this should be fixed anyway. But lets discuss other issues first.

Oleg.

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