[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);
}