sparc32: mm: Only call ctor()/dtor() functions for first and last user

The SRMMU page-table allocator allocates multiple PTE tables per page,
since they are only 1K in size. However, this means that calls to
pgtable_pte_page_{ctor,dtor}() must be serialised and performed only by
the first and last page-table allocation for the page respectively.

Use the page reference count to track how many PTE tables we have
allocated for a given page returned by the SRMMU allocator and only
call the ctor()/dtor() functions for the first and last user respectively.

Cc: David S. Miller <davem@davemloft.net>
Fixes: 8c8f3156dd40 ("sparc32: mm: Reduce allocation size for PMD and PTE tables")
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/arch/sparc/mm/srmmu.c b/arch/sparc/mm/srmmu.c
index 589370a..116d19a 100644 (file)
--- a/arch/sparc/mm/srmmu.c
+++ b/arch/sparc/mm/srmmu.c
@@ -364,9 +364,13 @@ pgtable_t pte_alloc_one(struct mm_struct *mm)
        if ((ptep = pte_alloc_one_kernel(mm)) == 0)
                return NULL;
        page = pfn_to_page(__nocache_pa((unsigned long)ptep) >> PAGE_SHIFT);
-       if (!pgtable_pte_page_ctor(page)) {
-               return NULL;
+       spin_lock(&mm->page_table_lock);
+       if (page_ref_inc_return(page) == 2 && !pgtable_pte_page_ctor(page)) {
+               page_ref_dec(page);
+               ptep = NULL;
        }
+       spin_unlock(&mm->page_table_lock);
+
        return ptep;
 }
 
@@ -375,7 +379,11 @@ void pte_free(struct mm_struct *mm, pgtable_t ptep)
        struct page *page;
 
        page = pfn_to_page(__nocache_pa((unsigned long)ptep) >> PAGE_SHIFT);
-       pgtable_pte_page_dtor(page);
+       spin_lock(&mm->page_table_lock);
+       if (page_ref_dec_return(page) == 1)
+               pgtable_pte_page_dtor(page);
+       spin_unlock(&mm->page_table_lock);
+
        srmmu_free_nocache(ptep, SRMMU_PTE_TABLE_SIZE);
 }