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

[Guenter Roeck]

On Mon, Nov 20, 2017 at 01:18:38PM -0500, Nicolas Pitre wrote:
> On Sun, 19 Nov 2017, Guenter Roeck wrote:
> 
> > 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)".
> 
> OK. the 0x2029b is the result of PAGE_SIZE being 8192 in your case.
> However the bootmem allocator deals with physical addresses not virtual 
> ones. So it shouldn't give you a 0x60000..0x61000 range.
> 
> Would be interesting to see what result you get on line 860 of 
> mm/bootmem.c.
> 
Nothing; __alloc_bootmem_low_node() is not called.

Call chain is:
  pcpu_alloc_alloc_info
    memblock_virt_alloc_nopanic
      __alloc_bootmem_nopanic
        ___alloc_bootmem_nopanic

and returns 0xc0536000.

Guenter