Subject: Re: 2.6.31-git5 kernel boot hangs on powerpc

From: Benjamin Herrenschmidt <[email-masked]>
Date: Fri, 25 Sep 2009 18:31:45 +1000

On Fri, 2009-09-25 at 16:39 +0900, Tejun Heo wrote:
> Hello,
> 
> Sachin Sant wrote:
> > <4>PERCPU: chunk 1 relocating -1 -> 18 c0000000db70fb00
> > <c0000000db70fb00:c0000000db70fb00>
> > <4>PERCPU: relocated <c000000001120320:c000000001120320>
> > <4>PERCPU: chunk 1 relocating 18 -> 16 c0000000db70fb00
> > <c000000001120320:c000000001120320>
> > <4>PERCPU: relocated <c000000001120300:c000000001120300>
> > <4>PERCPU: chunk 1, alloc pages [0,1)
> > <4>PERCPU: chunk 1, map pages [0,1)
> > <4>PERCPU: map 0xd00007fffff00000, 1 pages 53544
> > <4>PERCPU: map 0xd00007fffff80000, 1 pages 53545
> > <4>PERCPU: chunk 1, will clear 4096b/unit d00007fffff00000 d00007fffff80000
> > <3>INFO: RCU detected CPU 0 stall (t=1000 jiffies)
> 
> This supports my hypothesis.  This is the first area being allocated
> from a dynamic chunk and cleared.  PFN 53544 and 53545 have been
> allocated and successfully mapped to 0xd00007fffff00000 and
> 0xd00007fffff80000 using map_kernel_range_noflush() but when those
> addresses are actually accessed, we end up with infinite faults.  The
> fault handler probably thinks that the fault has been handled
> correctly but, when the control is returned, the processor faults
> again.  Benjamin, I'm way out of my depth here, can you please help?

Definitely looks like a powerpc mm problem. I'll have a look on monday.

Cheers,
Ben.

> Oh, one more simple experiment.  Sachin, does the following patch make
> any difference?
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 69511e6..93d29eb 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2102,7 +2102,8 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
>  				     size_t align, gfp_t gfp_mask)
>  {
>  	const unsigned long vmalloc_start = ALIGN(VMALLOC_START, align);
> -	const unsigned long vmalloc_end = VMALLOC_END & ~(align - 1);
> +	//const unsigned long vmalloc_end = VMALLOC_END & ~(align - 1);
> +	const unsigned long vmalloc_end = vmalloc_start + (512 << 20);
>  	struct vmap_area **vas, *prev, *next;
>  	struct vm_struct **vms;
>  	int area, area2, last_area, term_area;
> 
>