freebsd-5.4-stable panics

[Don Lewis]

On 30 Sep, John Baldwin wrote:
> On Friday 30 September 2005 11:25 am, Antoine Pelisse wrote:
>> On 9/30/05, John Baldwin <jhb at freebsd.org> wrote:
>> > On Friday 30 September 2005 05:24 am, Antoine Pelisse wrote:
>> > > Hi Robert,
>> > > I don't think your patch is correct, the total linked list can be
>> > > broken
>> > >
>> > > while the lock is released, thus just passing the link may not be
>> > > enough I have submitted a PR[1] for this a month ago but nobody took
>> > > care of it yet Regards,
>> > > Antoine Pelisse
>> > >
>> > > [1] http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/84684
>> >
>> > I think this patch looks ok. Robert, can you get the original panic on
>> > this
>> > thread tested against this patch?
>>
>>  I had a small program which could reproduce this panic in 10 seconds, it
>> was basically creating empty threads and calling kvm_getprocs() in the same
>> time. Anyway the patch was able to stop the program from panicing.
>> The panic is also reproducible in RELENG_6 and HEAD IIRC.
> 
> It turns out that the sysctl buffer is already wired in one of the two cases 
> that this function is called, so I moved the wiring up to the upper layer in 
> the other case and cut out a bunch of the locking gymnastics as a result.  
> Can you try this patch?
> 
> Index: kern_proc.c
> ===================================================================
> RCS file: /usr/cvs/src/sys/kern/kern_proc.c,v
> retrieving revision 1.231
> diff -u -r1.231 kern_proc.c
> --- kern_proc.c	27 Sep 2005 18:03:15 -0000	1.231
> +++ kern_proc.c	30 Sep 2005 17:04:57 -0000
> @@ -875,22 +875,16 @@
>  
>  	if (flags & KERN_PROC_NOTHREADS) {
>  		fill_kinfo_proc(p, &kinfo_proc);
> -		PROC_UNLOCK(p);
>  		error = SYSCTL_OUT(req, (caddr_t)&kinfo_proc,
>  				   sizeof(kinfo_proc));
> -		PROC_LOCK(p);
>  	} else {
> -		_PHOLD(p);
>  		FOREACH_THREAD_IN_PROC(p, td) {
>  			fill_kinfo_thread(td, &kinfo_proc);
> -			PROC_UNLOCK(p);
>  			error = SYSCTL_OUT(req, (caddr_t)&kinfo_proc,
>  					   sizeof(kinfo_proc));
> -			PROC_LOCK(p);
>  			if (error)
>  				break;
>  		}
> -		_PRELE(p);
>  	}
>  	PROC_UNLOCK(p);
>  	if (error)
> @@ -932,6 +926,9 @@
>  	if (oid_number == KERN_PROC_PID) {
>  		if (namelen != 1) 
>  			return (EINVAL);
> +		error = sysctl_wire_old_buffer(req, 0);
> +		if (error)
> +			return (error);		
>  		p = pfind((pid_t)name[0]);
>  		if (!p)
>  			return (ESRCH);
> 

sched_lock needs to be grabbed before the FOREACH_THREAD_IN_PROC loop.

Can _PHOLD()/_PRELE() be dropped?