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[PATCH] mm: init_mm without ptlock

Telusuri Sumber 
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>
This commit is contained in:
Hugh Dickins
2005-10-29 18:16:21 -07:00
committed by Linus Torvalds
orang tua 46dea3d092
melakukan 872fec16d9
26 mengubah file dengan 54 tambahan dan 114 penghapusan
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60
mm/memory.c
Melihat File

@@ -307,28 +307,22 @@ out:
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 @@ int __handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
#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 @@ pud_t fastcall *__pud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long addr
#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 @@ pmd_t fastcall *__pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long addr
#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 */