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Date:      Wed, 23 Mar 2011 16:34:34 +0200
From:      Kostik Belousov <kostikbel@gmail.com>
To:        John Baldwin <jhb@freebsd.org>
Cc:        svn-src-head@freebsd.org, Edward Tomasz Napierala <trasz@freebsd.org>, svn-src-all@freebsd.org, src-committers@freebsd.org, Julian Elischer <julian@freebsd.org>
Subject:   Re: svn commit: r219727 - head/sys/vm
Message-ID:  <20110323143434.GZ78089@deviant.kiev.zoral.com.ua>
In-Reply-To: <201103230945.37726.jhb@freebsd.org>
References:  <201103180647.p2I6lNCB051745@svn.freebsd.org> <4D831A82.7070308@freebsd.org> <201103230945.37726.jhb@freebsd.org>

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On Wed, Mar 23, 2011 at 09:45:37AM -0400, John Baldwin wrote:
> On Friday, March 18, 2011 4:40:34 am Julian Elischer wrote:
> > On 3/17/11 11:47 PM, Edward Tomasz Napierala wrote:
> > > Author: trasz
> > > Date: Fri Mar 18 06:47:23 2011
> > > New Revision: 219727
> > > URL: http://svn.freebsd.org/changeset/base/219727
> > >
> > > Log:
> > >    In vm_daemon(), when iterating over all processes in the system, s=
kip those
> > >    which are not yet fully initialized (i.e. ones with p_state =3D=3D=
 PRS_NEW).
> > >    Without it, we could panic in _thread_lock_flags().
> > >
> > >    Note that there may be other instances of FOREACH_PROC_IN_SYSTEM()=
 that
> > >    require similar fix.
> >=20
> > In the past each process was only put on the process list after it was=
=20
> > fully set up.
> > Did someone change that recently?  that would be "A Bad Thing" (TM).
>=20
> Err, no, that has never been true.  The reason it has to go on the list
> immediately is to reserve the PID against concurrent fork()s.
>=20
> Hmm, the locking of prs_state is a bit busted it seems.  Both the PROC_LO=
CK()
> and PROC_SLOCK() are supposed to be held when it is written to, but
> PROC_LOCK() is missing in fork1() when moving the state to PRS_NORMAL.
>=20
> Also, this commit should check against PRS_NORMAL after acquiring the proc
> lock, not before.
In the case of this commit, it does not matter much, I think. The reason
is that all the check want is to make sure that there is at least one
fully initialized thread linked into the process.

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