[PATCH] mm: ptd_alloc take ptlock
Second step in pushing down the page_table_lock. Remove the temporary
bridging hack from __pud_alloc, __pmd_alloc, __pte_alloc: expect callers not
to hold page_table_lock, whether it's on init_mm or a user mm; take
page_table_lock internally to check if a racing task already allocated.
Convert their callers from common code. But avoid coming back to change them
again later: instead of moving the spin_lock(&mm->page_table_lock) down,
switch over to new macros pte_alloc_map_lock and pte_unmap_unlock, which
encapsulate the mapping+locking and unlocking+unmapping together, and in the
end may use alternatives to the mm page_table_lock itself.
These callers all hold mmap_sem (some exclusively, some not), so at no level
can a page table be whipped away from beneath them; and pte_alloc uses the
"atomic" pmd_present to test whether it needs to allocate. It appears that on
all arches we can safely descend without page_table_lock.
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/fs/exec.c b/fs/exec.c
index 9bb55c8..ba73797 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -309,25 +309,24 @@
pud_t * pud;
pmd_t * pmd;
pte_t * pte;
+ spinlock_t *ptl;
if (unlikely(anon_vma_prepare(vma)))
- goto out_sig;
+ goto out;
flush_dcache_page(page);
pgd = pgd_offset(mm, address);
-
- spin_lock(&mm->page_table_lock);
pud = pud_alloc(mm, pgd, address);
if (!pud)
goto out;
pmd = pmd_alloc(mm, pud, address);
if (!pmd)
goto out;
- pte = pte_alloc_map(mm, pmd, address);
+ pte = pte_alloc_map_lock(mm, pmd, address, &ptl);
if (!pte)
goto out;
if (!pte_none(*pte)) {
- pte_unmap(pte);
+ pte_unmap_unlock(pte, ptl);
goto out;
}
inc_mm_counter(mm, anon_rss);
@@ -335,14 +334,11 @@
set_pte_at(mm, address, pte, pte_mkdirty(pte_mkwrite(mk_pte(
page, vma->vm_page_prot))));
page_add_anon_rmap(page, vma, address);
- pte_unmap(pte);
- spin_unlock(&mm->page_table_lock);
+ pte_unmap_unlock(pte, ptl);
/* no need for flush_tlb */
return;
out:
- spin_unlock(&mm->page_table_lock);
-out_sig:
__free_page(page);
force_sig(SIGKILL, current);
}
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 22c2d69..d4c3512 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -779,10 +779,28 @@
}
#endif /* CONFIG_MMU && !__ARCH_HAS_4LEVEL_HACK */
+#define pte_offset_map_lock(mm, pmd, address, ptlp) \
+({ \
+ spinlock_t *__ptl = &(mm)->page_table_lock; \
+ pte_t *__pte = pte_offset_map(pmd, address); \
+ *(ptlp) = __ptl; \
+ spin_lock(__ptl); \
+ __pte; \
+})
+
+#define pte_unmap_unlock(pte, ptl) do { \
+ spin_unlock(ptl); \
+ pte_unmap(pte); \
+} while (0)
+
#define pte_alloc_map(mm, pmd, address) \
((unlikely(!pmd_present(*(pmd))) && __pte_alloc(mm, pmd, address))? \
NULL: pte_offset_map(pmd, address))
+#define pte_alloc_map_lock(mm, pmd, address, ptlp) \
+ ((unlikely(!pmd_present(*(pmd))) && __pte_alloc(mm, pmd, address))? \
+ NULL: pte_offset_map_lock(mm, pmd, address, ptlp))
+
#define pte_alloc_kernel(pmd, address) \
((unlikely(!pmd_present(*(pmd))) && __pte_alloc_kernel(pmd, address))? \
NULL: pte_offset_kernel(pmd, address))
diff --git a/kernel/fork.c b/kernel/fork.c
index 2a587b3..8a06961 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -255,7 +255,6 @@
/*
* Link in the new vma and copy the page table entries.
*/
- spin_lock(&mm->page_table_lock);
*pprev = tmp;
pprev = &tmp->vm_next;
@@ -265,7 +264,6 @@
mm->map_count++;
retval = copy_page_range(mm, oldmm, tmp);
- spin_unlock(&mm->page_table_lock);
if (tmp->vm_ops && tmp->vm_ops->open)
tmp->vm_ops->open(tmp);
diff --git a/mm/fremap.c b/mm/fremap.c
index 49719a3..d862be3 100644
--- a/mm/fremap.c
+++ b/mm/fremap.c
@@ -63,23 +63,20 @@
pud_t *pud;
pgd_t *pgd;
pte_t pte_val;
+ spinlock_t *ptl;
BUG_ON(vma->vm_flags & VM_RESERVED);
pgd = pgd_offset(mm, addr);
- spin_lock(&mm->page_table_lock);
-
pud = pud_alloc(mm, pgd, addr);
if (!pud)
- goto err_unlock;
-
+ goto out;
pmd = pmd_alloc(mm, pud, addr);
if (!pmd)
- goto err_unlock;
-
- pte = pte_alloc_map(mm, pmd, addr);
+ goto out;
+ pte = pte_alloc_map_lock(mm, pmd, addr, &ptl);
if (!pte)
- goto err_unlock;
+ goto out;
/*
* This page may have been truncated. Tell the
@@ -89,10 +86,10 @@
inode = vma->vm_file->f_mapping->host;
size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
if (!page->mapping || page->index >= size)
- goto err_unlock;
+ goto unlock;
err = -ENOMEM;
if (page_mapcount(page) > INT_MAX/2)
- goto err_unlock;
+ goto unlock;
if (pte_none(*pte) || !zap_pte(mm, vma, addr, pte))
inc_mm_counter(mm, file_rss);
@@ -101,17 +98,15 @@
set_pte_at(mm, addr, pte, mk_pte(page, prot));
page_add_file_rmap(page);
pte_val = *pte;
- pte_unmap(pte);
update_mmu_cache(vma, addr, pte_val);
-
err = 0;
-err_unlock:
- spin_unlock(&mm->page_table_lock);
+unlock:
+ pte_unmap_unlock(pte, ptl);
+out:
return err;
}
EXPORT_SYMBOL(install_page);
-
/*
* Install a file pte to a given virtual memory address, release any
* previously existing mapping.
@@ -125,23 +120,20 @@
pud_t *pud;
pgd_t *pgd;
pte_t pte_val;
+ spinlock_t *ptl;
BUG_ON(vma->vm_flags & VM_RESERVED);
pgd = pgd_offset(mm, addr);
- spin_lock(&mm->page_table_lock);
-
pud = pud_alloc(mm, pgd, addr);
if (!pud)
- goto err_unlock;
-
+ goto out;
pmd = pmd_alloc(mm, pud, addr);
if (!pmd)
- goto err_unlock;
-
- pte = pte_alloc_map(mm, pmd, addr);
+ goto out;
+ pte = pte_alloc_map_lock(mm, pmd, addr, &ptl);
if (!pte)
- goto err_unlock;
+ goto out;
if (!pte_none(*pte) && zap_pte(mm, vma, addr, pte)) {
update_hiwater_rss(mm);
@@ -150,17 +142,13 @@
set_pte_at(mm, addr, pte, pgoff_to_pte(pgoff));
pte_val = *pte;
- pte_unmap(pte);
update_mmu_cache(vma, addr, pte_val);
- spin_unlock(&mm->page_table_lock);
- return 0;
-
-err_unlock:
- spin_unlock(&mm->page_table_lock);
+ pte_unmap_unlock(pte, ptl);
+ err = 0;
+out:
return err;
}
-
/***
* sys_remap_file_pages - remap arbitrary pages of a shared backing store
* file within an existing vma.
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ac5f044..ea0826f 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -277,12 +277,15 @@
unsigned long addr;
for (addr = vma->vm_start; addr < vma->vm_end; addr += HPAGE_SIZE) {
+ src_pte = huge_pte_offset(src, addr);
+ if (!src_pte)
+ continue;
dst_pte = huge_pte_alloc(dst, addr);
if (!dst_pte)
goto nomem;
+ spin_lock(&dst->page_table_lock);
spin_lock(&src->page_table_lock);
- src_pte = huge_pte_offset(src, addr);
- if (src_pte && !pte_none(*src_pte)) {
+ if (!pte_none(*src_pte)) {
entry = *src_pte;
ptepage = pte_page(entry);
get_page(ptepage);
@@ -290,6 +293,7 @@
set_huge_pte_at(dst, addr, dst_pte, entry);
}
spin_unlock(&src->page_table_lock);
+ spin_unlock(&dst->page_table_lock);
}
return 0;
@@ -354,7 +358,6 @@
hugetlb_prefault_arch_hook(mm);
- spin_lock(&mm->page_table_lock);
for (addr = vma->vm_start; addr < vma->vm_end; addr += HPAGE_SIZE) {
unsigned long idx;
pte_t *pte = huge_pte_alloc(mm, addr);
@@ -389,11 +392,12 @@
goto out;
}
}
+ spin_lock(&mm->page_table_lock);
add_mm_counter(mm, file_rss, HPAGE_SIZE / PAGE_SIZE);
set_huge_pte_at(mm, addr, pte, make_huge_pte(vma, page));
+ spin_unlock(&mm->page_table_lock);
}
out:
- spin_unlock(&mm->page_table_lock);
return ret;
}
diff --git a/mm/memory.c b/mm/memory.c
index 4bdd118..a40e4b1 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -282,14 +282,11 @@
int __pte_alloc(struct mm_struct *mm, pmd_t *pmd, unsigned long address)
{
- struct page *new;
-
- spin_unlock(&mm->page_table_lock);
- new = pte_alloc_one(mm, address);
- spin_lock(&mm->page_table_lock);
+ struct page *new = pte_alloc_one(mm, address);
if (!new)
return -ENOMEM;
+ spin_lock(&mm->page_table_lock);
if (pmd_present(*pmd)) /* Another has populated it */
pte_free(new);
else {
@@ -297,6 +294,7 @@
inc_page_state(nr_page_table_pages);
pmd_populate(mm, pmd, new);
}
+ spin_unlock(&mm->page_table_lock);
return 0;
}
@@ -344,9 +342,6 @@
* copy one vm_area from one task to the other. Assumes the page tables
* already present in the new task to be cleared in the whole range
* covered by this vma.
- *
- * dst->page_table_lock is held on entry and exit,
- * but may be dropped within p[mg]d_alloc() and pte_alloc_map().
*/
static inline void
@@ -419,17 +414,19 @@
unsigned long addr, unsigned long end)
{
pte_t *src_pte, *dst_pte;
+ spinlock_t *src_ptl, *dst_ptl;
int progress = 0;
int rss[2];
again:
rss[1] = rss[0] = 0;
- dst_pte = pte_alloc_map(dst_mm, dst_pmd, addr);
+ dst_pte = pte_alloc_map_lock(dst_mm, dst_pmd, addr, &dst_ptl);
if (!dst_pte)
return -ENOMEM;
src_pte = pte_offset_map_nested(src_pmd, addr);
+ src_ptl = &src_mm->page_table_lock;
+ spin_lock(src_ptl);
- spin_lock(&src_mm->page_table_lock);
do {
/*
* We are holding two locks at this point - either of them
@@ -438,8 +435,8 @@
if (progress >= 32) {
progress = 0;
if (need_resched() ||
- need_lockbreak(&src_mm->page_table_lock) ||
- need_lockbreak(&dst_mm->page_table_lock))
+ need_lockbreak(src_ptl) ||
+ need_lockbreak(dst_ptl))
break;
}
if (pte_none(*src_pte)) {
@@ -449,12 +446,12 @@
copy_one_pte(dst_mm, src_mm, dst_pte, src_pte, vma, addr, rss);
progress += 8;
} while (dst_pte++, src_pte++, addr += PAGE_SIZE, addr != end);
- spin_unlock(&src_mm->page_table_lock);
+ spin_unlock(src_ptl);
pte_unmap_nested(src_pte - 1);
- pte_unmap(dst_pte - 1);
add_mm_rss(dst_mm, rss[0], rss[1]);
- cond_resched_lock(&dst_mm->page_table_lock);
+ pte_unmap_unlock(dst_pte - 1, dst_ptl);
+ cond_resched();
if (addr != end)
goto again;
return 0;
@@ -1049,8 +1046,9 @@
unsigned long addr, unsigned long end, pgprot_t prot)
{
pte_t *pte;
+ spinlock_t *ptl;
- pte = pte_alloc_map(mm, pmd, addr);
+ pte = pte_alloc_map_lock(mm, pmd, addr, &ptl);
if (!pte)
return -ENOMEM;
do {
@@ -1062,7 +1060,7 @@
BUG_ON(!pte_none(*pte));
set_pte_at(mm, addr, pte, zero_pte);
} while (pte++, addr += PAGE_SIZE, addr != end);
- pte_unmap(pte - 1);
+ pte_unmap_unlock(pte - 1, ptl);
return 0;
}
@@ -1112,14 +1110,12 @@
BUG_ON(addr >= end);
pgd = pgd_offset(mm, addr);
flush_cache_range(vma, addr, end);
- spin_lock(&mm->page_table_lock);
do {
next = pgd_addr_end(addr, end);
err = zeromap_pud_range(mm, pgd, addr, next, prot);
if (err)
break;
} while (pgd++, addr = next, addr != end);
- spin_unlock(&mm->page_table_lock);
return err;
}
@@ -1133,8 +1129,9 @@
unsigned long pfn, pgprot_t prot)
{
pte_t *pte;
+ spinlock_t *ptl;
- pte = pte_alloc_map(mm, pmd, addr);
+ pte = pte_alloc_map_lock(mm, pmd, addr, &ptl);
if (!pte)
return -ENOMEM;
do {
@@ -1142,7 +1139,7 @@
set_pte_at(mm, addr, pte, pfn_pte(pfn, prot));
pfn++;
} while (pte++, addr += PAGE_SIZE, addr != end);
- pte_unmap(pte - 1);
+ pte_unmap_unlock(pte - 1, ptl);
return 0;
}
@@ -1210,7 +1207,6 @@
pfn -= addr >> PAGE_SHIFT;
pgd = pgd_offset(mm, addr);
flush_cache_range(vma, addr, end);
- spin_lock(&mm->page_table_lock);
do {
next = pgd_addr_end(addr, end);
err = remap_pud_range(mm, pgd, addr, next,
@@ -1218,7 +1214,6 @@
if (err)
break;
} while (pgd++, addr = next, addr != end);
- spin_unlock(&mm->page_table_lock);
return err;
}
EXPORT_SYMBOL(remap_pfn_range);
@@ -1985,17 +1980,9 @@
* with external mmu caches can use to update those (ie the Sparc or
* PowerPC hashed page tables that act as extended TLBs).
*
- * Note the "page_table_lock". It is to protect against kswapd removing
- * pages from under us. Note that kswapd only ever _removes_ pages, never
- * adds them. As such, once we have noticed that the page is not present,
- * we can drop the lock early.
- *
- * The adding of pages is protected by the MM semaphore (which we hold),
- * so we don't need to worry about a page being suddenly been added into
- * our VM.
- *
- * We enter with the pagetable spinlock held, we are supposed to
- * release it when done.
+ * We enter with non-exclusive mmap_sem (to exclude vma changes,
+ * but allow concurrent faults), and pte mapped but not yet locked.
+ * We return with mmap_sem still held, but pte unmapped and unlocked.
*/
static inline int handle_pte_fault(struct mm_struct *mm,
struct vm_area_struct *vma, unsigned long address,
@@ -2003,6 +1990,7 @@
{
pte_t entry;
+ spin_lock(&mm->page_table_lock);
entry = *pte;
if (!pte_present(entry)) {
if (pte_none(entry)) {
@@ -2051,30 +2039,18 @@
if (unlikely(is_vm_hugetlb_page(vma)))
return hugetlb_fault(mm, vma, address, write_access);
- /*
- * We need the page table lock to synchronize with kswapd
- * and the SMP-safe atomic PTE updates.
- */
pgd = pgd_offset(mm, address);
- spin_lock(&mm->page_table_lock);
-
pud = pud_alloc(mm, pgd, address);
if (!pud)
- goto oom;
-
+ return VM_FAULT_OOM;
pmd = pmd_alloc(mm, pud, address);
if (!pmd)
- goto oom;
-
+ return VM_FAULT_OOM;
pte = pte_alloc_map(mm, pmd, address);
if (!pte)
- goto oom;
-
- return handle_pte_fault(mm, vma, address, pte, pmd, write_access);
+ return VM_FAULT_OOM;
- oom:
- spin_unlock(&mm->page_table_lock);
- return VM_FAULT_OOM;
+ return handle_pte_fault(mm, vma, address, pte, pmd, write_access);
}
#ifndef __PAGETABLE_PUD_FOLDED
@@ -2084,24 +2060,16 @@
*/
int __pud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address)
{
- pud_t *new;
-
- if (mm != &init_mm) /* Temporary bridging hack */
- spin_unlock(&mm->page_table_lock);
- new = pud_alloc_one(mm, address);
- if (!new) {
- if (mm != &init_mm) /* Temporary bridging hack */
- spin_lock(&mm->page_table_lock);
+ pud_t *new = pud_alloc_one(mm, address);
+ if (!new)
return -ENOMEM;
- }
spin_lock(&mm->page_table_lock);
if (pgd_present(*pgd)) /* Another has populated it */
pud_free(new);
else
pgd_populate(mm, pgd, new);
- if (mm == &init_mm) /* Temporary bridging hack */
- spin_unlock(&mm->page_table_lock);
+ spin_unlock(&mm->page_table_lock);
return 0;
}
#endif /* __PAGETABLE_PUD_FOLDED */
@@ -2113,16 +2081,9 @@
*/
int __pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
{
- pmd_t *new;
-
- if (mm != &init_mm) /* Temporary bridging hack */
- spin_unlock(&mm->page_table_lock);
- new = pmd_alloc_one(mm, address);
- if (!new) {
- if (mm != &init_mm) /* Temporary bridging hack */
- spin_lock(&mm->page_table_lock);
+ pmd_t *new = pmd_alloc_one(mm, address);
+ if (!new)
return -ENOMEM;
- }
spin_lock(&mm->page_table_lock);
#ifndef __ARCH_HAS_4LEVEL_HACK
@@ -2136,8 +2097,7 @@
else
pgd_populate(mm, pud, new);
#endif /* __ARCH_HAS_4LEVEL_HACK */
- if (mm == &init_mm) /* Temporary bridging hack */
- spin_unlock(&mm->page_table_lock);
+ spin_unlock(&mm->page_table_lock);
return 0;
}
#endif /* __PAGETABLE_PMD_FOLDED */
diff --git a/mm/mremap.c b/mm/mremap.c
index 616facc..8de77b6 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -28,9 +28,6 @@
pud_t *pud;
pmd_t *pmd;
- /*
- * We don't need page_table_lock: we have mmap_sem exclusively.
- */
pgd = pgd_offset(mm, addr);
if (pgd_none_or_clear_bad(pgd))
return NULL;
@@ -50,25 +47,20 @@
{
pgd_t *pgd;
pud_t *pud;
- pmd_t *pmd = NULL;
+ pmd_t *pmd;
- /*
- * We do need page_table_lock: because allocators expect that.
- */
- spin_lock(&mm->page_table_lock);
pgd = pgd_offset(mm, addr);
pud = pud_alloc(mm, pgd, addr);
if (!pud)
- goto out;
+ return NULL;
pmd = pmd_alloc(mm, pud, addr);
if (!pmd)
- goto out;
+ return NULL;
if (!pmd_present(*pmd) && __pte_alloc(mm, pmd, addr))
- pmd = NULL;
-out:
- spin_unlock(&mm->page_table_lock);
+ return NULL;
+
return pmd;
}
@@ -80,6 +72,7 @@
struct address_space *mapping = NULL;
struct mm_struct *mm = vma->vm_mm;
pte_t *old_pte, *new_pte, pte;
+ spinlock_t *old_ptl;
if (vma->vm_file) {
/*
@@ -95,9 +88,8 @@
new_vma->vm_truncate_count = 0;
}
- spin_lock(&mm->page_table_lock);
- old_pte = pte_offset_map(old_pmd, old_addr);
- new_pte = pte_offset_map_nested(new_pmd, new_addr);
+ old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
+ new_pte = pte_offset_map_nested(new_pmd, new_addr);
for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
new_pte++, new_addr += PAGE_SIZE) {
@@ -110,8 +102,7 @@
}
pte_unmap_nested(new_pte - 1);
- pte_unmap(old_pte - 1);
- spin_unlock(&mm->page_table_lock);
+ pte_unmap_unlock(old_pte - 1, old_ptl);
if (mapping)
spin_unlock(&mapping->i_mmap_lock);
}