Date: Tue, 13 Mar 2007 22:43:29 +0100 From: Pawel Jakub Dawidek <pjd@FreeBSD.org> To: Julian Elischer <julian@elischer.org> Cc: FreeBSD Current <current@freebsd.org> Subject: Re: proc lock might become an sx lock? Message-ID: <20070313214329.GB3932@garage.freebsd.pl> In-Reply-To: <45F0D1F5.9010200@elischer.org> References: <45F0D1F5.9010200@elischer.org>
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On Thu, Mar 08, 2007 at 07:18:13PM -0800, Julian Elischer wrote:
> currently the thread list in the process is protected by the sched lock.
> for a process with a lot of threads this is probably not a good idea.
> I experimented with making it protected by the proc loc, but the followin=
g sort of thing happens a lot:
>=20
> sx_slock(&allproc_lock);
> FOREACH_PROC_IN_SYSTEM(p) {
> mtx_lock_spin(&sched_lock);
> FOREACH_THREAD_IN_PROC(p, td) {
> ...
> }
> mtx_unlock_spin(&sched_lock);
>=20
> Changing the protection of the thread list to use the proc lock would
> replace the sched_lock with the proc lock, but.....
> this has a problem.. the proc lock is a mutex and can therefore not be in=
side the
> allproc_lock.
Why not? Acquiring sx lock first and then a mutex is fine. The other way
around is illegal.
> and in fact you get:
>=20
> Trying to mount root from ufs:/dev/aacd0s1d
> panic: blockable sleep lock (sleep mutex) process lock @ kern/sched_4bsd.=
c:383
This is because it's order is hardcoded in subr_witness.c.
Move:
{ "process lock", &lock_class_mtx_sleep },
a bit up and change lock_class_mtx_sleep to lock_class_sx.
PS. I'm not familiar with schedulers, so I don't know if sched_lock can
be replaced there.
--=20
Pawel Jakub Dawidek http://www.wheel.pl
pjd@FreeBSD.org http://www.FreeBSD.org
FreeBSD committer Am I Evil? Yes, I Am!
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