[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>

2 files changed, 1 insertions, 8 deletions

diff --git a/arch/ppc64/mm/imalloc.c b/arch/ppc64/mm/imalloc.c
index c65b87b92756..f4ca29cf5364 100644
--- a/arch/ppc64/mm/imalloc.c
+++ b/arch/ppc64/mm/imalloc.c
@@ -300,12 +300,7 @@ void im_free(void * addr)
         for (p = &imlist ; (tmp = *p) ; p = &tmp->next) {
                 if (tmp->addr == addr) {
                         *p = tmp->next;
-
-                        /* XXX: do we need the lock? */
-                        spin_lock(&init_mm.page_table_lock);
                         unmap_vm_area(tmp);
-                        spin_unlock(&init_mm.page_table_lock);
-
                         kfree(tmp);
                         up(&imlist_sem);
                         return;
diff --git a/arch/ppc64/mm/init.c b/arch/ppc64/mm/init.c
index be64b157afce..a45584b3440c 100644
--- a/arch/ppc64/mm/init.c
+++ b/arch/ppc64/mm/init.c
@@ -155,7 +155,6 @@ static int map_io_page(unsigned long ea, unsigned long pa, int flags)
         unsigned long vsid;
 
         if (mem_init_done) {
-                spin_lock(&init_mm.page_table_lock);
                 pgdp = pgd_offset_k(ea);
                 pudp = pud_alloc(&init_mm, pgdp, ea);
                 if (!pudp)
@@ -163,12 +162,11 @@ static int map_io_page(unsigned long ea, unsigned long pa, int flags)
                 pmdp = pmd_alloc(&init_mm, pudp, ea);
                 if (!pmdp)
                         return -ENOMEM;
-                ptep = pte_alloc_kernel(&init_mm, pmdp, ea);
+                ptep = pte_alloc_kernel(pmdp, ea);
                 if (!ptep)
                         return -ENOMEM;
                 set_pte_at(&init_mm, ea, ptep, pfn_pte(pa >> PAGE_SHIFT,
                                                           __pgprot(flags)));
-                spin_unlock(&init_mm.page_table_lock);
         } else {
                 unsigned long va, vpn, hash, hpteg;