Date: Thu, 31 Mar 2011 12:34:31 -0400 From: Attilio Rao <attilio@freebsd.org> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-current@freebsd.org, Svatopluk Kraus <onwahe@gmail.com> Subject: Re: schedcpu() in /sys/kern/sched_4bsd.c calls thread_lock() on thread with un-initialized td_lock Message-ID: <AANLkTikLexFE5ZZGkJ%2BUq1udkfs14jVFuvmak%2B-srfdv@mail.gmail.com> In-Reply-To: <201103310958.51416.jhb@freebsd.org> References: <AANLkTimEiOW%2BkSZD6n1MHiRou3UWibU6Oy3fr9RO4_O4@mail.gmail.com> <201103310958.51416.jhb@freebsd.org>
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2011/3/31 John Baldwin <jhb@freebsd.org>:
> On Thursday, March 31, 2011 7:32:26 am Svatopluk Kraus wrote:
>> Hi,
>>
>> =C2=A0 I've got a page fault (because of NULL td_lock) in
>> thread_lock_flags() called from schedcpu() in /sys/kern/sched_4bsd.c
>> file. During process fork, new thread is linked to new process which
>> is linked to allproc list and both allproc_lock and new process lock
>> are unlocked before sched_fork() is called, where new thread td_lock
>> is initialized. Only PRS_NEW process status is on sentry but not
>> checked in schedcpu().
>
> I think this should fix it:
>
> Index: sched_4bsd.c
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> --- sched_4bsd.c =C2=A0 =C2=A0 =C2=A0 =C2=A0(revision 220190)
> +++ sched_4bsd.c =C2=A0 =C2=A0 =C2=A0 =C2=A0(working copy)
> @@ -463,6 +463,10 @@ schedcpu(void)
> =C2=A0 =C2=A0 =C2=A0 =C2=A0sx_slock(&allproc_lock);
> =C2=A0 =C2=A0 =C2=A0 =C2=A0FOREACH_PROC_IN_SYSTEM(p) {
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0PROC_LOCK(p);
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 if (p->p_state =3D=3D =
PRS_NEW) {
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 PROC_UNLOCK(p);
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 continue;
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 }
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0FOREACH_THREAD_IN_=
PROC(p, td) {
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0awake =3D 0;
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0thread_lock(td);
>
I don't really think this fix is right because otherwise, when using
sched_4bsd anytime we are going to scan the thread list within a proc
we need to check for PRS_NEW.
We likely need to change the init scheme for the td_lock by having a
scheduler primitive setting it and doing that on thread_init() UMA
constructor, or similar approach.
Attilio
--=20
Peace can only be achieved by understanding - A. Einstein
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