Merge branch 'sparc32-SRMMU-fixes-for-SMP'

Will Deacon says:

====================
sparc32 SRMMU fixes for SMP

Enabling SMP for sparc32 uncovered some issues in the SRMMU page-table
allocation code. One of these was introduced by me, but the other two
seem to have been there a while and are probably just exposed more
easily by my recent changes.

Tested on QEMU. I'm assuming these will go via David's tree.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/sparc/mm/srmmu.c

@@ -364,10 +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)) {
-		__free_page(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;
 }
 
@@ -376,7 +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);
+	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);
 }
 

mm/Kconfig

@@ -192,6 +192,9 @@ config MEMORY_HOTREMOVE
 # Default to 4 for wider testing, though 8 might be more appropriate.
 # ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
 # PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes.
+# SPARC32 allocates multiple pte tables within a single page, and therefore
+# a per-page lock leads to problems when multiple tables need to be locked
+# at the same time (e.g. copy_page_range()).
 # DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page.
 #
 config SPLIT_PTLOCK_CPUS
@@ -199,6 +202,7 @@ config SPLIT_PTLOCK_CPUS
 	default "999999" if !MMU
 	default "999999" if ARM && !CPU_CACHE_VIPT
 	default "999999" if PARISC && !PA20
+	default "999999" if SPARC32
 	default "4"
 
 config ARCH_ENABLE_SPLIT_PMD_PTLOCK