linux-kernel - Re: freezer problems

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]

Date:	Tue, 20 Feb 2007 01:41:41 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	ego@...ibm.com, akpm@...l.org, paulmck@...ibm.com, mingo@...e.hu,
	vatsa@...ibm.com, dipankar@...ibm.com,
	venkatesh.pallipadi@...el.com, linux-kernel@...r.kernel.org,
	Pavel Machek <pavel@....cz>
Subject: Re: freezer problems

On 02/19, Rafael J. Wysocki wrote:
>
> On Monday, 19 February 2007 21:23, Oleg Nesterov wrote:
> 
> > > @@ -199,6 +189,10 @@ static void thaw_tasks(int thaw_user_spa
> > >
> > >         do_each_thread(g, p) {
> > > +               if (freezer_should_skip(p))
> > > +                       cancel_freezing(p);
> > > +       } while_each_thread(g, p);
> > > +       do_each_thread(g, p) {
> > >                 if (!freezeable(p))
> > >                         continue;
> > 
> > Any reason for 2 separate do_each_thread() loops ?
> 
> Yes.  If there is a "freeze" request pending for the vfork parent (TIF_FREEZE
> set), we have to cancel it before the child is unfrozen, since otherwise the
> parent may go freezing after we try to reset PF_FROZEN for it.

I see, thanks... thaw_process() doesn't take TIF_FREEZE into account.

But doesn't this mean we have a race?

Suppose that try_to_freeze_tasks() failed. It does cancel_freezing() for each
process before return, but what if some thread already checked TIF_FREEZE and
(for simplicity) it is preempted before frozen_process() in refrigerator().

thaw_tasks() runs, ignores this task (P), returns. P gets CPU, and becomes
frozen, but nobody will thaw it.

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/