[PATCH 11/21] mm: ptd_alloc take ptlock

From: Hugh Dickins
Date: Wed Oct 12 2005 - 19:57:31 EST

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@xxxxxxxxxxx>
---

fs/exec.c | 14 ++-----
include/linux/mm.h | 18 +++++++++
kernel/fork.c | 2 -
mm/fremap.c | 46 ++++++++---------------
mm/hugetlb.c | 12 ++++--
mm/memory.c | 104 ++++++++++++++++-------------------------------------
mm/mremap.c | 27 ++++---------
7 files changed, 89 insertions(+), 134 deletions(-)

--- mm10/fs/exec.c 2005-10-11 23:54:33.000000000 +0100
+++ mm11/fs/exec.c 2005-10-11 23:56:25.000000000 +0100
@@ -309,25 +309,24 @@ void install_arg_page(struct vm_area_str
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 @@ void install_arg_page(struct vm_area_str
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);
}
--- mm10/include/linux/mm.h 2005-10-11 23:56:11.000000000 +0100
+++ mm11/include/linux/mm.h 2005-10-11 23:56:25.000000000 +0100
@@ -784,10 +784,28 @@ static inline pmd_t *pmd_alloc(struct mm
}
#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))
--- mm10/kernel/fork.c 2005-09-30 11:59:12.000000000 +0100
+++ mm11/kernel/fork.c 2005-10-11 23:56:25.000000000 +0100
@@ -255,7 +255,6 @@ static inline int dup_mmap(struct mm_str
/*
* 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 @@ static inline int dup_mmap(struct mm_str

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);
--- mm10/mm/fremap.c 2005-10-11 23:54:33.000000000 +0100
+++ mm11/mm/fremap.c 2005-10-11 23:56:25.000000000 +0100
@@ -63,23 +63,20 @@ int install_page(struct mm_struct *mm, s
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
@@ -89,7 +86,7 @@ int install_page(struct mm_struct *mm, s
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;

if (pte_none(*pte) || !zap_pte(mm, vma, addr, pte))
inc_mm_counter(mm, file_rss);
@@ -98,17 +95,15 @@ int install_page(struct mm_struct *mm, s
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.
@@ -122,23 +117,20 @@ int install_file_pte(struct mm_struct *m
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);
@@ -147,17 +139,13 @@ int install_file_pte(struct mm_struct *m

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.
--- mm10/mm/hugetlb.c 2005-10-11 23:54:33.000000000 +0100
+++ mm11/mm/hugetlb.c 2005-10-11 23:56:25.000000000 +0100
@@ -276,12 +276,15 @@ int copy_hugetlb_page_range(struct mm_st
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);
@@ -289,6 +292,7 @@ int copy_hugetlb_page_range(struct mm_st
set_huge_pte_at(dst, addr, dst_pte, entry);
}
spin_unlock(&src->page_table_lock);
+ spin_unlock(&dst->page_table_lock);
}
return 0;

@@ -353,7 +357,6 @@ int hugetlb_prefault(struct address_spac

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);
@@ -388,11 +391,12 @@ int hugetlb_prefault(struct address_spac
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;
}

--- mm10/mm/memory.c 2005-10-11 23:56:11.000000000 +0100
+++ mm11/mm/memory.c 2005-10-11 23:56:25.000000000 +0100
@@ -282,14 +282,11 @@ void free_pgtables(struct mmu_gather **t

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 @@ int __pte_alloc(struct mm_struct *mm, pm
inc_page_state(nr_page_table_pages);
pmd_populate(mm, pmd, new);
}
+ spin_unlock(&mm->page_table_lock);
return 0;
}

@@ -344,9 +342,6 @@ void print_bad_pte(struct vm_area_struct
* 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 @@ static int copy_pte_range(struct mm_stru
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 @@ again:
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 @@ again:
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 @@ static int zeromap_pte_range(struct mm_s
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 @@ static int zeromap_pte_range(struct mm_s
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 @@ int zeromap_page_range(struct vm_area_st
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 @@ static int remap_pte_range(struct mm_str
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 @@ static int remap_pte_range(struct mm_str
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 @@ int remap_pfn_range(struct vm_area_struc
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 @@ int remap_pfn_range(struct vm_area_struc
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 @@ static int do_file_page(struct mm_struct
* 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 @@ static inline int handle_pte_fault(struc
{
pte_t entry;

+ spin_lock(&mm->page_table_lock);
entry = *pte;
if (!pte_present(entry)) {
if (pte_none(entry)) {
@@ -2051,30 +2039,18 @@ int __handle_mm_fault(struct mm_struct *
if (is_vm_hugetlb_page(vma))
return VM_FAULT_SIGBUS; /* mapping truncation does this. */

- /*
- * 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 __handle_mm_fault(struct mm_struct *
*/
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 __pud_alloc(struct mm_struct *mm, pg
*/
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 @@ int __pmd_alloc(struct mm_struct *mm, pu
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 */
--- mm10/mm/mremap.c 2005-10-11 23:56:11.000000000 +0100
+++ mm11/mm/mremap.c 2005-10-11 23:56:25.000000000 +0100
@@ -28,9 +28,6 @@ static pmd_t *get_old_pmd(struct mm_stru
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 @@ static pmd_t *alloc_new_pmd(struct mm_st
{
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 @@ static void move_ptes(struct vm_area_str
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 @@ static void move_ptes(struct vm_area_str
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 @@ static void move_ptes(struct vm_area_str
}

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);
}
-
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