linux-kernel - Re: [question] perf

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>] [day] [month] [year] [list]

Date:	Mon, 11 Apr 2011 15:21:21 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Metzger, Markus T" <markus.t.metzger@...el.com>
Cc:	"mingo@...e.hu" <mingo@...e.hu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [question] perf_event, ptrace

On Mon, 2011-04-11 at 14:12 +0100, Metzger, Markus T wrote:
> Hi Ingo, Peter,
> 
>  
> 
> When I use perf_event together with ptrace (i.e. when the ptracer is the
> event owner), are there any guarantees whether events have been drained when
> the ptracer is notified?
> 
>  
> 
> When I look at the signal handling code (kernel/signal.c:ptrace_stop(), line
> 1682), it appears as if the ptracee first wakes up the ptracer and then
> calls schedule().
> 
>  
> 
> Thus, if ptracer and ptracee run on different cpus, the ptracer might
> already be looking at the event buffer when the ptracee is scheduled out and
> the last events are drained.
> 
>  
> 
> Am I reading this correctly?
> 
>  
> 
> Is the ptracer expected to check ->data_head to see if there had been any
> updates?

I've got absolutely no clue about ptrace anything. One would expect
ptrace to provide proper notification of when the ptracee is stopped, at
which point staring at ->data_head seems like the right thing to do if
you want to figure out if new events have happened.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/