[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>
diff --git a/mm/memory.c b/mm/memory.c
index 692ad81..95a4553 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -307,28 +307,22 @@
return pte_offset_map(pmd, address);
}
-pte_t fastcall * pte_alloc_kernel(struct mm_struct *mm, pmd_t *pmd, unsigned long address)
+pte_t fastcall * pte_alloc_kernel(pmd_t *pmd, unsigned long address)
{
if (!pmd_present(*pmd)) {
pte_t *new;
- spin_unlock(&mm->page_table_lock);
- new = pte_alloc_one_kernel(mm, address);
- spin_lock(&mm->page_table_lock);
+ new = pte_alloc_one_kernel(&init_mm, address);
if (!new)
return NULL;
- /*
- * Because we dropped the lock, we should re-check the
- * entry, as somebody else could have populated it..
- */
- if (pmd_present(*pmd)) {
+ spin_lock(&init_mm.page_table_lock);
+ if (pmd_present(*pmd))
pte_free_kernel(new);
- goto out;
- }
- pmd_populate_kernel(mm, pmd, new);
+ else
+ pmd_populate_kernel(&init_mm, pmd, new);
+ spin_unlock(&init_mm.page_table_lock);
}
-out:
return pte_offset_kernel(pmd, address);
}
@@ -2097,30 +2091,30 @@
#ifndef __PAGETABLE_PUD_FOLDED
/*
* Allocate page upper directory.
- *
- * We've already handled the fast-path in-line, and we own the
- * page table lock.
+ * We've already handled the fast-path in-line.
*/
pud_t fastcall *__pud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address)
{
pud_t *new;
- spin_unlock(&mm->page_table_lock);
+ if (mm != &init_mm) /* Temporary bridging hack */
+ spin_unlock(&mm->page_table_lock);
new = pud_alloc_one(mm, address);
- spin_lock(&mm->page_table_lock);
- if (!new)
+ if (!new) {
+ if (mm != &init_mm) /* Temporary bridging hack */
+ spin_lock(&mm->page_table_lock);
return NULL;
+ }
- /*
- * Because we dropped the lock, we should re-check the
- * entry, as somebody else could have populated it..
- */
+ spin_lock(&mm->page_table_lock);
if (pgd_present(*pgd)) {
pud_free(new);
goto out;
}
pgd_populate(mm, pgd, new);
out:
+ if (mm == &init_mm) /* Temporary bridging hack */
+ spin_unlock(&mm->page_table_lock);
return pud_offset(pgd, address);
}
#endif /* __PAGETABLE_PUD_FOLDED */
@@ -2128,24 +2122,22 @@
#ifndef __PAGETABLE_PMD_FOLDED
/*
* Allocate page middle directory.
- *
- * We've already handled the fast-path in-line, and we own the
- * page table lock.
+ * We've already handled the fast-path in-line.
*/
pmd_t fastcall *__pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
{
pmd_t *new;
- spin_unlock(&mm->page_table_lock);
+ if (mm != &init_mm) /* Temporary bridging hack */
+ spin_unlock(&mm->page_table_lock);
new = pmd_alloc_one(mm, address);
- spin_lock(&mm->page_table_lock);
- if (!new)
+ if (!new) {
+ if (mm != &init_mm) /* Temporary bridging hack */
+ spin_lock(&mm->page_table_lock);
return NULL;
+ }
- /*
- * Because we dropped the lock, we should re-check the
- * entry, as somebody else could have populated it..
- */
+ spin_lock(&mm->page_table_lock);
#ifndef __ARCH_HAS_4LEVEL_HACK
if (pud_present(*pud)) {
pmd_free(new);
@@ -2161,6 +2153,8 @@
#endif /* __ARCH_HAS_4LEVEL_HACK */
out:
+ if (mm == &init_mm) /* Temporary bridging hack */
+ spin_unlock(&mm->page_table_lock);
return pmd_offset(pud, address);
}
#endif /* __PAGETABLE_PMD_FOLDED */