Re: panic: uma_zone_slab is looping

On Sun, Dec 26, 2004 at 11:02:16PM -0500, Bosko Milekic wrote:
> 
> >   I'll have to reserve some more time to think about this.  One way I
> >   think it might be solvable would be to change that check that
> >   triggers the NULL return explicitly check for the bucketzone, and not
> >   for all UMA_ZONE_INTERNAL zones; I need to think this through a little
> >   more.
> 
>   Please try the attached patch and let me know if with it you can or
>   cannot trigger the original (seemingly infinite) looping.  Although I
>   still haven't quite figured out how the described scenario could lead
>   to infinite looping exactly (I did conclude that it could lead to some
>   looping, though), the patch is worth trying as I believe the scenario
>   *could* occur.
> 

After more than 18 hours of testing with your patch I ran into a
(unrelated ?) "panic: mutex vm object not owned":
http://www.holm.cc/stress/log/freeze06.html

> -- 
> Bosko Milekic
> bmilekic_at_technokratis.com
> bmilekic_at_FreeBSD.org

> Index: uma_core.c
> ===================================================================
> RCS file: /home/ncvs/src/sys/vm/uma_core.c,v
> retrieving revision 1.111
> diff -u -r1.111 uma_core.c
> --- uma_core.c	26 Dec 2004 00:35:12 -0000	1.111
> +++ uma_core.c	27 Dec 2004 03:58:25 -0000
> _at__at_ -1939,9 +1939,19 _at__at_
>  	 * buckets there too we will recurse in kmem_alloc and bad
>  	 * things happen.  So instead we return a NULL bucket, and make
>  	 * the code that allocates buckets smart enough to deal with it
> +	 *
> +	 * XXX: While we want this protection for the bucket zones so that
> +	 * recursion from the VM is handled (and the calling code that
> +	 * allocates buckets knows how to deal with it), we do not want
> +	 * to prevent allocation from the slab header zones (slabzone
> +	 * and slabrefzone) if uk_recurse is not zero for them.  The
> +	 * reason is that it could lead to NULL being returned for
> +	 * slab header allocations even in the M_WAITOK case, and the
> +	 * caller can't handle that. 
>  	 */
>  	if (keg->uk_flags & UMA_ZFLAG_INTERNAL && keg->uk_recurse != 0)
> -		return (NULL);
> +		if ((zone != slabzone) && (zone != slabrefzone))
> +			return (NULL);
>  
>  	slab = NULL;
>  


-- 
Peter Holm