linux-kernel - Re: [Question] Hooks for scheduler tracing (CFS)

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

Message-ID: <20070726162231.GB30643@redhat.com>
Date:	Thu, 26 Jul 2007 12:22:31 -0400
From:	"Frank Ch. Eigler" <fche@...hat.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Ankita Garg <ankita@...ibm.com>,
	Arjan van de Ven <arjan@...radead.org>, linux@...mer.net,
	LKML <linux-kernel@...r.kernel.org>,
	RT-Users <linux-rt-users@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [Question] Hooks for scheduler tracing (CFS)

Hi -

On Thu, Jul 26, 2007 at 11:02:26AM -0400, Mathieu Desnoyers wrote:
> [...]
> > > The problem is also in _stp_print_flush, not *only* in relay code:
> > > void _stp_print_flush (void)
> > > ...
> > >                 spin_lock(&_stp_print_lock);
> > >                 spin_unlock(&_stp_print_lock);
> > > 
> > > Those will turn into mutexes with -rt.
> > 
> > Indeed,

(Though actually that bug was fixed some time ago.)


> > plus systemtap-generated locking code uses rwlocks,
> > local_irq_save/restore or preempt_disable, in various places.  Could
> > someone point to a place that spells out what would be more
> > appropriate way of ensuring atomicity while being compatible with -rt?
> 
> AFAIK, for your needs either:
> [...]
> - Use per-cpu data with preempt disabling/irq disabling

As in local_irq_save / preempt_disable?  Yes, already done.

> - Use the original "real" spin locks/rwlocks (raw_*).
> [...]

It was unclear from the OLS paper whether the spin_lock_irq* family of
functions also had to be moved to the raw forms.

> You just don't want to sleep in the tracing code. [...]  Since you
> will likely disable preemption, make sure your tracing code executes
> in a deterministic time.

Definitely, that has always been the case.

> Make sure that the sub-buffer switch code respects that too [...]

We will review that part of the related code.

- FChE
-
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/