linux-kernel - Re: Q: perf_event && event->owner

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 for Android: free password hash cracker in your pocket

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

Date:	Tue, 9 Nov 2010 18:42:20 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Prasad <prasad@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Q: perf_event && event->owner

On 11/09, Peter Zijlstra wrote:
>
> Ah,.. quite so. So how about we explicitly destroy the list when the
> task dies?

Yes, I think it makes sense to destroy the list and set ->owner = NULL.
If we reset the owner, we can also avoid get_task_struct().

The only problem is perf_event_release_kernel(), it can race with the
exiting event->owner. It can do get_task_struct() under rcu lock temporary,
just to take the mutex and remove the entry.

> > And ptrace(), it doesn't use sys_perf_event_open() to create the event.
>
> Right, I guess it uses kernel based things, I guess we could not add
> kernel based counters to the list.

Agreed, another case when event->owner should be NULL.

Hmm. With or without these changes. Shouldn't perf_event_release_kernel()
remove the event from list before anything else? Otherwise, afaics a thread
which does close(event_fd) can race with creator doing prctl(EVENTS_ENABLE),
no?

Oleg.

--
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/