[PATCH] fix get_user_pages bug
Checking pte_dirty instead of pte_write in __follow_page is problematic
for s390, and for copy_one_pte which leaves dirty when clearing write.
So revert __follow_page to check pte_write as before, and make
do_wp_page pass back a special extra VM_FAULT_WRITE bit to say it has
done its full job: once get_user_pages receives this value, it no longer
requires pte_write in __follow_page.
But most callers of handle_mm_fault, in the various architectures, have
switch statements which do not expect this new case. To avoid changing
them all in a hurry, make an inline wrapper function (using the old
name) that masks off the new bit, and use the extended interface with
double underscores.
Yes, we do have a call to do_wp_page from do_swap_page, but no need to
change that: in rare case it's needed, another do_wp_page will follow.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
[ Cleanups by Nick Piggin ]
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/mm/memory.c b/mm/memory.c
index 2405289..81d7117 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -811,15 +811,18 @@
pte = *ptep;
pte_unmap(ptep);
if (pte_present(pte)) {
- if (write && !pte_dirty(pte))
+ if (write && !pte_write(pte))
goto out;
if (read && !pte_read(pte))
goto out;
pfn = pte_pfn(pte);
if (pfn_valid(pfn)) {
page = pfn_to_page(pfn);
- if (accessed)
+ if (accessed) {
+ if (write && !pte_dirty(pte) &&!PageDirty(page))
+ set_page_dirty(page);
mark_page_accessed(page);
+ }
return page;
}
}
@@ -941,10 +944,11 @@
}
spin_lock(&mm->page_table_lock);
do {
+ int write_access = write;
struct page *page;
cond_resched_lock(&mm->page_table_lock);
- while (!(page = follow_page(mm, start, write))) {
+ while (!(page = follow_page(mm, start, write_access))) {
/*
* Shortcut for anonymous pages. We don't want
* to force the creation of pages tables for
@@ -957,7 +961,16 @@
break;
}
spin_unlock(&mm->page_table_lock);
- switch (handle_mm_fault(mm,vma,start,write)) {
+ switch (__handle_mm_fault(mm, vma, start,
+ write_access)) {
+ case VM_FAULT_WRITE:
+ /*
+ * do_wp_page has broken COW when
+ * necessary, even if maybe_mkwrite
+ * decided not to set pte_write
+ */
+ write_access = 0;
+ /* FALLTHRU */
case VM_FAULT_MINOR:
tsk->min_flt++;
break;
@@ -1220,6 +1233,7 @@
struct page *old_page, *new_page;
unsigned long pfn = pte_pfn(pte);
pte_t entry;
+ int ret;
if (unlikely(!pfn_valid(pfn))) {
/*
@@ -1247,7 +1261,7 @@
lazy_mmu_prot_update(entry);
pte_unmap(page_table);
spin_unlock(&mm->page_table_lock);
- return VM_FAULT_MINOR;
+ return VM_FAULT_MINOR|VM_FAULT_WRITE;
}
}
pte_unmap(page_table);
@@ -1274,6 +1288,7 @@
/*
* Re-check the pte - we dropped the lock
*/
+ ret = VM_FAULT_MINOR;
spin_lock(&mm->page_table_lock);
page_table = pte_offset_map(pmd, address);
if (likely(pte_same(*page_table, pte))) {
@@ -1290,12 +1305,13 @@
/* Free the old page.. */
new_page = old_page;
+ ret |= VM_FAULT_WRITE;
}
pte_unmap(page_table);
page_cache_release(new_page);
page_cache_release(old_page);
spin_unlock(&mm->page_table_lock);
- return VM_FAULT_MINOR;
+ return ret;
no_new_page:
page_cache_release(old_page);
@@ -1987,7 +2003,6 @@
if (write_access) {
if (!pte_write(entry))
return do_wp_page(mm, vma, address, pte, pmd, entry);
-
entry = pte_mkdirty(entry);
}
entry = pte_mkyoung(entry);
@@ -2002,7 +2017,7 @@
/*
* By the time we get here, we already hold the mm semaphore
*/
-int handle_mm_fault(struct mm_struct *mm, struct vm_area_struct * vma,
+int __handle_mm_fault(struct mm_struct *mm, struct vm_area_struct * vma,
unsigned long address, int write_access)
{
pgd_t *pgd;