Re: (bisected) parisc boot crash in post-5.8 git - pgalloc changes

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

Hi,

On Sat, Aug 15, 2020 at 07:42:00PM +0100, Matthew Wilcox wrote:
> On Sat, Aug 15, 2020 at 09:35:05PM +0300, Meelis Roos wrote:
> > > While 5.8.0 worked fine on my HP RP2470 (Gentoo with 10.2.0 kgcc), yesterdays dddcbc139e96 and todays a1d21081a60d crash on boot. I have started bisecting it.
> > 
> > And finished now. I included all CC-s and SOB-s from the commit to this mail - sorry if too broad.
> > 
> > 1355c31eeb7ea61a7f2f2937d17cd4e343a6b5af is the first bad commit
> 
> yes, I see the problem.
> 
> arch/parisc/include/asm/pgtable.h:#define PMD_ORDER     1 /* Number of pages per pmd */
> 
> -static inline pmd_t *pmd_alloc_one(struct mm_struct *mm, unsigned long address)
> -{
> -       pmd_t *pmd = (pmd_t *)__get_free_pages(GFP_KERNEL, PMD_ORDER);
> 
> +       page = alloc_pages(gfp, 0);
> 
> So I think the quick fix is to restore the parisc pmd_alloc_one and define
> __HAVE_ARCH_PMD_ALLOC_ONE.  I wasn't following this series too closely,
> so I shan't propose a patch, but leave it up to Mike.  I'd probably miss
> some subtlety.

You are right, I've missed that parisc has PMD_ORDER != 0 and the
simplest fix would be to revert changes to parisc pmd_alloc_one().

Meelis, can you please try the below patch:

diff --git a/arch/parisc/include/asm/pgalloc.h b/arch/parisc/include/asm/pgalloc.h
index cc7ecc2ef55d..a6482b2ce0ea 100644
--- a/arch/parisc/include/asm/pgalloc.h
+++ b/arch/parisc/include/asm/pgalloc.h
@@ -10,6 +10,7 @@
 
 #include <asm/cache.h>
 
+#define __HAVE_ARCH_PMD_ALLOC_ONE
 #define __HAVE_ARCH_PMD_FREE
 #define __HAVE_ARCH_PGD_FREE
 #include <asm-generic/pgalloc.h>
@@ -67,6 +68,11 @@ static inline void pud_populate(struct mm_struct *mm, pud_t *pud, pmd_t *pmd)
 			(__u32)(__pa((unsigned long)pmd) >> PxD_VALUE_SHIFT)));
 }
 
+static inline pmd_t *pmd_alloc_one(struct mm_struct *mm, unsigned long address)
+{
+	return (pmd_t *)__get_free_pages(GFP_PGTABLE_KERNEL, PMD_ORDER);
+}
+
 static inline void pmd_free(struct mm_struct *mm, pmd_t *pmd)
 {
 	if (pmd_flag(*pmd) & PxD_FLAG_ATTACHED) {

-- 
Sincerely yours,
Mike.