Re: mm/percpu.c: use smarter memory allocation for struct pcpu_alloc_info (crisv32 hang)

[Guenter Roeck]

On 11/19/2017 08:08 PM, Nicolas Pitre wrote:
> On Sun, 19 Nov 2017, Guenter Roeck wrote:
> > On 11/19/2017 12:36 PM, Nicolas Pitre wrote:
> > > On Sat, 18 Nov 2017, Guenter Roeck wrote:
> > > > On Tue, Oct 03, 2017 at 06:29:49PM -0400, Nicolas Pitre wrote:
> > > > > @@ -2295,6 +2295,7 @@ void __init setup_per_cpu_areas(void)
> > > > >      	if (pcpu_setup_first_chunk(ai, fc) < 0)
> > > > >    		panic("Failed to initialize percpu areas.");
> > > > > +	pcpu_free_alloc_info(ai);
> > > >
> > > > This is the culprit. Everything works fine if I remove this line.
> > >
> > > Without this line, the memory at the ai pointer is leaked. Maybe this is
> > > modifying the memory allocation pattern and that triggers a bug later on
> > > in your case.
> > >
> > > At that point the console driver is not yet initialized and any error
> > > message won't be printed. You should enable the early console mechanism
> > > in your kernel (see arch/cris/arch-v32/kernel/debugport.c) and see what
> > > that might tell you.
> >
> > The problem is that BUG() on crisv32 does not yield useful output.
> > Anyway, here is the culprit.
> >
> > diff --git a/mm/bootmem.c b/mm/bootmem.c
> > index 6aef64254203..2bcc8901450c 100644
> > --- a/mm/bootmem.c
> > +++ b/mm/bootmem.c
> > @@ -382,7 +382,8 @@ static int __init mark_bootmem(unsigned long start,
> > unsigned long end,
> >                          return 0;
> >                  pos = bdata->node_low_pfn;
> >          }
> > -       BUG();
> > +       WARN(1, "mark_bootmem(): memory range 0x%lx-0x%lx not found\n", start,
> > end);
> > +       return -ENOMEM;
> >   }
> >
> >   /**
> > diff --git a/mm/percpu.c b/mm/percpu.c
> > index 79e3549cab0f..c75622d844f1 100644
> > --- a/mm/percpu.c
> > +++ b/mm/percpu.c
> > @@ -1881,6 +1881,7 @@ struct pcpu_alloc_info * __init
> > pcpu_alloc_alloc_info(int nr_groups,
> >    */
> >   void __init pcpu_free_alloc_info(struct pcpu_alloc_info *ai)
> >   {
> > +       printk("pcpu_free_alloc_info(%p (0x%lx))\n", ai, __pa(ai));
> >          memblock_free_early(__pa(ai), ai->__ai_size);
>
> The problem here is that there is two possibilities for
> memblock_free_early(). From include/linux/bootmem.h:
>
> #if defined(CONFIG_HAVE_MEMBLOCK) && defined(CONFIG_NO_BOOTMEM)
>
> static inline void __init memblock_free_early(
>                                          phys_addr_t base, phys_addr_t size)
> {
>          __memblock_free_early(base, size);
> }
>
> #else
>
> static inline void __init memblock_free_early(
>                                          phys_addr_t base, phys_addr_t size)
> {
>          free_bootmem(base, size);
> }
>
> #endif
>
> It looks like most architectures use the memblock variant, including all
> the ones I have access to.
>
> > results in:
> >
> > pcpu_free_alloc_info(c0534000 (0x40534000))
> > ------------[ cut here ]------------
> > WARNING: CPU: 0 PID: 0 at mm/bootmem.c:385 mark_bootmem+0x9a/0xaa
> > mark_bootmem(): memory range 0x2029a-0x2029b not found
>
> Well... PFN_UP(0x40534000) should give 0x40534. How you might end up
> with 0x2029a in mark_bootmem(), let alone not exit on the first "if (max
> == end) return 0;" within the loop is rather weird.
pcpu_free_alloc_info: ai=c0536000, __pa(ai)=0x40536000, PFN_UP(__pa(ai))=0x2029b, PFN_UP(ai)=0x6029b

bootmem range is 0x60000..0x61000. It doesn't get to "if (max == end)"
because "pos (=0x2029b) < bdata->node_min_pfn (=0x60000)".

Guenter