Re: [PATCH v2 3/3] arm: extend pfn_valid to take into accound freed memory map alignment

[Mike Rapoport <rppt@linux.ibm.com>]

Hi Tony,

On Mon, Jun 28, 2021 at 01:20:11PM +0300, Tony Lindgren wrote:
> Hi,
> 
> Looks like this patch causes a boot regression at least for Cortex-A15.
> That's commit 990e6d0e1de8 ("arm: extend pfn_valid to take into accound
> freed memory map alignment") in Linux next.
> 
> Most of the time I see the following on beagle-x15 right after init starts:
> 
> Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
> CPU0: stopping
> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.13.0-rc7-next-20210625 #100
> Hardware name: Generic DRA74X (Flattened Device Tree)
> [<c0110c54>] (unwind_backtrace) from [<c010b408>] (show_stack+0x10/0x14)
> [<c010b408>] (show_stack) from [<c09fae04>] (dump_stack_lvl+0x40/0x4c)
> [<c09fae04>] (dump_stack_lvl) from [<c010e768>] (do_handle_IPI+0x2c8/0x334)
> [<c010e768>] (do_handle_IPI) from [<c010e7e8>] (ipi_handler+0x14/0x20)
> [<c010e7e8>] (ipi_handler) from [<c01a5f14>] (handle_percpu_devid_irq+0xa8/0x22c)
> [<c01a5f14>] (handle_percpu_devid_irq) from [<c019fc78>] (handle_domain_irq+0x64/0xa4)
> [<c019fc78>] (handle_domain_irq) from [<c05b9bdc>] (gic_handle_irq+0x88/0xb0)
> [<c05b9bdc>] (gic_handle_irq) from [<c0100b6c>] (__irq_svc+0x6c/0x90)
> Exception stack(0xc0f01f08 to 0xc0f01f50)
> 1f00:                   00000f38 00000f37 00000000 fe600000 c0ff90c0 00000000
> 1f20: c0f0520c c0f05260 00000000 c0f00000 00000000 c0e788f0 00000000 c0f01f58
> 1f40: c0126aa0 c0107dc4 60000013 ffffffff
> [<c0100b6c>] (__irq_svc) from [<c0107dc4>] (arch_cpu_idle+0x1c/0x3c)
> [<c0107dc4>] (arch_cpu_idle) from [<c0a098d8>] (default_idle_call+0x38/0xe0)
> [<c0a098d8>] (default_idle_call) from [<c0172860>] (do_idle+0x214/0x2cc)
> [<c0172860>] (do_idle) from [<c0172c0c>] (cpu_startup_entry+0x18/0x1c)
> [<c0172c0c>] (cpu_startup_entry) from [<c0e00ef8>] (start_kernel+0x5cc/0x6c4)
> 
> Sometimes the system boots to console, but maybe only about 20% of the
> time. Reverting 990e6d0e1de8 makes Linux next boot again for me.

Can you please send log with 'memblock=debug' added to the command line?
 
> Regards,
> 
> Tony
> 
> #regzb introduced: 990e6d0e1de8 ("arm: extend pfn_valid to take into accound freed memory map alignment")
> 
> 
> * Mike Rapoport <rppt@kernel.org> [700101 02:00]:
> > From: Mike Rapoport <rppt@linux.ibm.com>
> > 
> > When unused memory map is freed the preserved part of the memory map is
> > extended to match pageblock boundaries because lots of core mm
> > functionality relies on homogeneity of the memory map within pageblock
> > boundaries.
> > 
> > Since pfn_valid() is used to check whether there is a valid memory map
> > entry for a PFN, make it return true also for PFNs that have memory map
> > entries even if there is no actual memory populated there.
> > 
> > Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> > ---
> >  arch/arm/mm/init.c | 13 ++++++++++++-
> >  1 file changed, 12 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
> > index 9d4744a632c6..6162a070a410 100644
> > --- a/arch/arm/mm/init.c
> > +++ b/arch/arm/mm/init.c
> > @@ -125,11 +125,22 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max_low,
> >  int pfn_valid(unsigned long pfn)
> >  {
> >  	phys_addr_t addr = __pfn_to_phys(pfn);
> > +	unsigned long pageblock_size = PAGE_SIZE * pageblock_nr_pages;
> >  
> >  	if (__phys_to_pfn(addr) != pfn)
> >  		return 0;
> >  
> > -	return memblock_is_map_memory(addr);
> > +	/*
> > +	 * If address less than pageblock_size bytes away from a present
> > +	 * memory chunk there still will be a memory map entry for it
> > +	 * because we round freed memory map to the pageblock boundaries.
> > +	 */
> > +	if (memblock_overlaps_region(&memblock.memory,
> > +				     ALIGN_DOWN(addr, pageblock_size),
> > +				     pageblock_size))
> > +		return 1;
> > +
> > +	return 0;
> >  }
> >  EXPORT_SYMBOL(pfn_valid);
> >  #endif
> > -- 
> > 2.28.0
> > 

-- 
Sincerely yours,
Mike.