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Subject[patch] ksm: check for ERR_PTR from follow_page()
The follow_page() function can potentially return -EFAULT so I added 
checks for this.

Also I silenced an uninitialized variable warning on my version of gcc
(version 4.3.2).

Signed-off-by: Dan Carpenter <error27@gmail.com>
---
I'm not very familiar with this code, so handle with care.

diff --git a/mm/ksm.c b/mm/ksm.c
index 8cdfc2a..956880f 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -365,7 +365,7 @@ static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
do {
cond_resched();
page = follow_page(vma, addr, FOLL_GET);
- if (!page)
+ if (IS_ERR_OR_NULL(page))
break;
if (PageKsm(page))
ret = handle_mm_fault(vma->vm_mm, vma, addr,
@@ -447,7 +447,7 @@ static struct page *get_mergeable_page(struct rmap_item *rmap_item)
goto out;

page = follow_page(vma, addr, FOLL_GET);
- if (!page)
+ if (IS_ERR_OR_NULL(page))
goto out;
if (PageAnon(page)) {
flush_anon_page(vma, page, addr);
@@ -1086,7 +1086,7 @@ struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
cond_resched();
tree_rmap_item = rb_entry(*new, struct rmap_item, node);
tree_page = get_mergeable_page(tree_rmap_item);
- if (!tree_page)
+ if (IS_ERR_OR_NULL(tree_page))
return NULL;

/*
@@ -1294,7 +1294,7 @@ next_mm:
if (ksm_test_exit(mm))
break;
*page = follow_page(vma, ksm_scan.address, FOLL_GET);
- if (*page && PageAnon(*page)) {
+ if (!IS_ERR_OR_NULL(*page) && PageAnon(*page)) {
flush_anon_page(vma, *page, ksm_scan.address);
flush_dcache_page(*page);
rmap_item = get_next_rmap_item(slot,
@@ -1308,7 +1308,7 @@ next_mm:
up_read(&mm->mmap_sem);
return rmap_item;
}
- if (*page)
+ if (!IS_ERR_OR_NULL(*page))
put_page(*page);
ksm_scan.address += PAGE_SIZE;
cond_resched();
@@ -1367,7 +1367,7 @@ next_mm:
static void ksm_do_scan(unsigned int scan_npages)
{
struct rmap_item *rmap_item;
- struct page *page;
+ struct page *uninitialized_var(page);

while (scan_npages--) {
cond_resched();

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