[PATCH] mm: init_mm without ptlock

First step in pushing down the page_table_lock.  init_mm.page_table_lock has
been used throughout the architectures (usually for ioremap): not to serialize
kernel address space allocation (that's usually vmlist_lock), but because
pud_alloc,pmd_alloc,pte_alloc_kernel expect caller holds it.

Reverse that: don't lock or unlock init_mm.page_table_lock in any of the
architectures; instead rely on pud_alloc,pmd_alloc,pte_alloc_kernel to take
and drop it when allocating a new one, to check lest a racing task already
did.  Similarly no page_table_lock in vmalloc's map_vm_area.

Some temporary ugliness in __pud_alloc and __pmd_alloc: since they also handle
user mms, which are converted only by a later patch, for now they have to lock
differently according to whether or not it's init_mm.

If sources get muddled, there's a danger that an arch source taking
init_mm.page_table_lock will be mixed with common source also taking it (or
neither take it).  So break the rules and make another change, which should
break the build for such a mismatch: remove the redundant mm arg from
pte_alloc_kernel (ppc64 scrapped its distinct ioremap_mm in 2.6.13).

Exceptions: arm26 used pte_alloc_kernel on user mm, now pte_alloc_map; ia64
used pte_alloc_map on init_mm, now pte_alloc_kernel; parisc had bad args to
pmd_alloc and pte_alloc_kernel in unused USE_HPPA_IOREMAP code; ppc64
map_io_page forgot to unlock on failure; ppc mmu_mapin_ram and ppc64 im_free
took page_table_lock for no good reason.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 3 insertions, 8 deletions

diff --git a/arch/ia64/mm/init.c b/arch/ia64/mm/init.c
index 0063b2c..e3215ba 100644
--- a/arch/ia64/mm/init.c
+++ b/arch/ia64/mm/init.c
@@ -275,26 +275,21 @@ put_kernel_page (struct page *page, unsigned long address, pgprot_t pgprot)
 
 	pgd = pgd_offset_k(address);		/* note: this is NOT pgd_offset()! */
 
-	spin_lock(&init_mm.page_table_lock);
 	{
 		pud = pud_alloc(&init_mm, pgd, address);
 		if (!pud)
 			goto out;
-
 		pmd = pmd_alloc(&init_mm, pud, address);
 		if (!pmd)
 			goto out;
-		pte = pte_alloc_map(&init_mm, pmd, address);
+		pte = pte_alloc_kernel(pmd, address);
 		if (!pte)
 			goto out;
-		if (!pte_none(*pte)) {
-			pte_unmap(pte);
+		if (!pte_none(*pte))
 			goto out;
-		}
 		set_pte(pte, mk_pte(page, pgprot));
-		pte_unmap(pte);
 	}
-  out:	spin_unlock(&init_mm.page_table_lock);
+  out:
 	/* no need for flush_tlb */
 	return page;
 }