linux-kernel - Re: [linux-pm] 2.6.21-rc4-mm1: freezing of processes broken

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Message-ID: <20070321024701.GC13436@us.ibm.com>
Date:	Tue, 20 Mar 2007 19:47:01 -0700
From:	sukadev@...ibm.com
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Jiri Slaby <jirislaby@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Machek <pavel@....cz>, linux-pm@...ts.osdl.org,
	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...sign.ru>
Subject: Re: [linux-pm] 2.6.21-rc4-mm1: freezing of processes broken

Eric W. Biederman [ebiederm@...ssion.com] wrote:
| "Rafael J. Wysocki" <rjw@...k.pl> writes:
| 
| > On Tuesday, 20 March 2007 22:06, Rafael J. Wysocki wrote:
| >> On Tuesday, 20 March 2007 21:58, Jiri Slaby wrote:
| >> > Rafael J. Wysocki napsal(a):
| >> > > Actually, the problem is 100% reproducible on my system too and I doubt
| > it's
| >> > > caused by the recent freezer patches.
| >> > 
| >> > I don't know what exactly do you mean by recent, but 2.6.21-rc3-mm2 works
| >> > for me.
| >> 
| >> Thanks for the confirmation.
| >> 
| >> The patches I was talking about had already been in 2.6.21-rc3-mm2, so the
| >> reason of this failure must be different.
| >
| > Bisection shows that the freezing of processes has been broken by one of the
| > patches:
| >
| > remove-the-likelypid-check-in-copy_process.patch
| 
| Grr.  Oleg's review of remove-the-likelypid-check-in-copy-process
| showed it to be questionable (and it was just an optimization)
| so we can get rid of that one easily. 
| 
| Although all it did that was really questionable was add
| the idle process to the global process list and bump a process
| count when we forked the idle process.  Not dramatically dangerous
| things.
| 
| > use-task_pgrp-task_session-in-copy_process.patch
| 
| As I recall that patch was pretty trivial, and shouldn't have
| anything to do with the freezer.   The process freezer doesn't care
| about pids does it?

Yes. I think this one is trivial too. Here is the effective change in
copy_process():

-               attach_pid(p, PIDTYPE_PGID, find_pid(pgid));
-               attach_pid(p, PIDTYPE_SID, find_pid(sid));
+               attach_pid(p, PIDTYPE_PGID, task_pgrp(current));
+               attach_pid(p, PIDTYPE_SID, task_session(current));


| 
| Eric
-
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