do_wp_page_mk_pte_writable was rather broken: page_mkwrite is for shared
pages, whereas the code it was trying to share was for private pages, as
the recent addition of a PageAnon test there has made more explicit.
Sort that out and reabsorb it into do_wp_page: hch and others found that
separation less than helpful. And page_cache_get on the old_page before
page_table_lock is dropped - nothing else stabilizes the page in there.
Signed-off-by: Hugh Dickins <[email protected]>
---
mm/memory.c | 113 +++++++++++++++++++++++++++---------------------------------
1 files changed, 51 insertions(+), 62 deletions(-)
--- 2.6.13-rc2-mm2/mm/memory.c 2005-07-07 12:33:21.000000000 +0100
+++ linux/mm/memory.c 2005-07-11 20:01:28.000000000 +0100
@@ -1199,58 +1199,6 @@ static inline void break_cow(struct vm_a
}
/*
- * Make a PTE writeable for do_wp_page() on a shared-writable page
- */
-static inline int do_wp_page_mk_pte_writable(struct mm_struct *mm,
- struct vm_area_struct *vma,
- unsigned long address,
- pmd_t *pmd,
- pte_t *page_table,
- struct page *old_page,
- pte_t pte)
-{
- pte_t entry;
-
- /* See if the VMA's owner wants to know that the page is about to
- * become writable */
- if (vma->vm_ops && vma->vm_ops->page_mkwrite) {
- /* Notify the page owner without the lock held so they can
- * sleep if they want to */
- pte_unmap(page_table);
- spin_unlock(&mm->page_table_lock);
-
- if (vma->vm_ops->page_mkwrite(vma, old_page) < 0)
- goto bus_error;
-
- spin_lock(&mm->page_table_lock);
-
- /* Since we dropped the lock we need to revalidate the PTE as
- * someone else may have changed it. If they did, we just
- * return, as we can count on the MMU to tell us if they didn't
- * also make it writable
- */
- page_table = pte_offset_map(pmd, address);
- if (!pte_same(*page_table, pte))
- goto minor_fault;
- }
-
- flush_cache_page(vma, address, page_to_pfn(old_page));
- entry = maybe_mkwrite(pte_mkyoung(pte_mkdirty(pte)),
- vma);
- ptep_set_access_flags(vma, address, page_table, entry, 1);
- update_mmu_cache(vma, address, entry);
- lazy_mmu_prot_update(entry);
- pte_unmap(page_table);
-
- minor_fault:
- spin_unlock(&mm->page_table_lock);
- return VM_FAULT_MINOR;
-
- bus_error:
- return VM_FAULT_SIGBUS;
-}
-
-/*
* This routine handles present pages, when users try to write
* to a shared page. It is done by copying the page to a new address
* and decrementing the shared-page counter for the old page.
@@ -1275,6 +1223,8 @@ static int do_wp_page(struct mm_struct *
{
struct page *old_page, *new_page;
unsigned long pfn = pte_pfn(pte);
+ pte_t entry;
+ int reuse;
if (unlikely(!pfn_valid(pfn))) {
/*
@@ -1290,21 +1240,53 @@ static int do_wp_page(struct mm_struct *
}
old_page = pfn_to_page(pfn);
- if (PageAnon(old_page) && !TestSetPageLocked(old_page)) {
- int reuse = can_share_swap_page(old_page);
- unlock_page(old_page);
- if (reuse) {
- /* We can just make the PTE writable */
- return do_wp_page_mk_pte_writable(mm, vma, address, pmd,
- page_table, old_page,
- pte);
+ if (unlikely(vma->vm_flags & VM_SHARED)) {
+ if (vma->vm_ops && vma->vm_ops->page_mkwrite) {
+ /*
+ * Notify the page owner without the lock held,
+ * so they can sleep if they want to.
+ */
+ pte_unmap(page_table);
+ if (!PageReserved(old_page))
+ page_cache_get(old_page);
+ spin_unlock(&mm->page_table_lock);
+
+ if (vma->vm_ops->page_mkwrite(vma, old_page) < 0)
+ goto unwritable_page;
+
+ spin_lock(&mm->page_table_lock);
+ page_cache_release(old_page);
+
+ /*
+ * Since we dropped the lock we need to revalidate
+ * the PTE as someone else may have changed it. If
+ * they did, we just return, as we can count on the
+ * MMU to tell us if they didn't also make it writable.
+ */
+ page_table = pte_offset_map(pmd, address);
+ if (!pte_same(*page_table, pte))
+ goto success;
}
+ reuse = 1;
+ } else if (PageAnon(old_page) && !TestSetPageLocked(old_page)) {
+ reuse = can_share_swap_page(old_page);
+ unlock_page(old_page);
+ } else
+ reuse = 0;
+
+ if (reuse) {
+ flush_cache_page(vma, address, pfn);
+ entry = maybe_mkwrite(pte_mkyoung(pte_mkdirty(pte)), vma);
+ ptep_set_access_flags(vma, address, page_table, entry, 1);
+ update_mmu_cache(vma, address, entry);
+ lazy_mmu_prot_update(entry);
+ goto success;
}
- pte_unmap(page_table);
/*
* Ok, we need to copy. Oh, well..
*/
+ pte_unmap(page_table);
if (!PageReserved(old_page))
page_cache_get(old_page);
spin_unlock(&mm->page_table_lock);
@@ -1321,6 +1303,7 @@ static int do_wp_page(struct mm_struct *
goto no_new_page;
copy_user_highpage(new_page, old_page, address);
}
+
/*
* Re-check the pte - we dropped the lock
*/
@@ -1341,15 +1324,21 @@ static int do_wp_page(struct mm_struct *
/* Free the old page.. */
new_page = old_page;
}
- pte_unmap(page_table);
page_cache_release(new_page);
page_cache_release(old_page);
+
+success:
+ pte_unmap(page_table);
spin_unlock(&mm->page_table_lock);
return VM_FAULT_MINOR;
no_new_page:
page_cache_release(old_page);
return VM_FAULT_OOM;
+
+unwritable_page:
+ page_cache_release(old_page);
+ return VM_FAULT_SIGBUS;
}
/*
-
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