BUG FIX?: mm->rss is modified in some places without holding the page_table_lock

tytso
2000-11-03T11:40:23Z

I'm in the process of updating the 2.4 bug list for test10, and as near
as I can tell, there was a lot of discussion about two different ways of
fixing this bug:

> 9. To Do
> * mm->rss is modified in some places without holding the
> page_table_lock (sct)

To wit, either making mm->rss an atomic_t (which doesn't quite work for
some architectures which need it to be 64 bits), or putting in some
locks as Dave Jones suggested.

As far as I can tell, neither patch has gone in, and discussion seems to
have dropped in the past two weeks or so. An examination of the kernel
seems to indicate that neither fixed has been taken. What's the status
of this? Given that we don't have a 64-bit atomic_t type, what do
people think of Davej's patch? (attached, below)

- Ted

diff -urN --exclude-from=/home/davej/.exclude linux/mm/memory.c linux.dj/mm/memory.c
--- linux/mm/memory.c Sat Sep 16 00:51:21 2000
+++ linux.dj/mm/memory.c Wed Oct 11 23:41:10 2000
@@ -370,7 +370,6 @@
address = (address + PGDIR_SIZE) & PGDIR_MASK;
dir++;
} while (address && (address < end));
- spin_unlock(&mm->page_table_lock);
/*
* Update rss for the mm_struct (not necessarily current->mm)
* Notice that rss is an unsigned long.
@@ -379,6 +378,7 @@
mm->rss -= freed;
else
mm->rss = 0;
+ spin_unlock(&mm->page_table_lock);
}

@@ -1074,7 +1074,9 @@
flush_icache_page(vma, page);
}

+ spin_lock(&mm->page_table_lock);
mm->rss++;
+ spin_unlock(&mm->page_table_lock);

pte = mk_pte(page, vma->vm_page_prot);

@@ -1113,7 +1115,9 @@
return -1;
clear_user_highpage(page, addr);
entry = pte_mkwrite(pte_mkdirty(mk_pte(page, vma->vm_page_prot)));
+ spin_lock(&mm->page_table_lock);
mm->rss++;
+ spin_unlock(&mm->page_table_lock);
flush_page_to_ram(page);
}
set_pte(page_table, entry);
@@ -1152,7 +1156,9 @@
return 0;
if (new_page == NOPAGE_OOM)
return -1;
+ spin_lock(&mm->page_table_lock);
++mm->rss;
+ spin_unlock(&mm->page_table_lock);
/*
* This silly early PAGE_DIRTY setting removes a race
* due to the bad i386 page protection. But it's valid
diff -urN --exclude-from=/home/davej/.exclude linux/mm/mmap.c linux.dj/mm/mmap.c
--- linux/mm/mmap.c Tue Aug 29 20:41:12 2000
+++ linux.dj/mm/mmap.c Wed Oct 11 23:48:30 2000
@@ -844,7 +844,9 @@
vmlist_modify_lock(mm);
mm->mmap = mm->mmap_avl = mm->mmap_cache = NULL;
vmlist_modify_unlock(mm);
+ spin_lock (&mm->page_table_lock);
mm->rss = 0;
+ spin_unlock (&mm->page_table_lock);
mm->total_vm = 0;
mm->locked_vm = 0;
while (mpnt) {
diff -urN --exclude-from=/home/davej/.exclude linux/mm/vmscan.c linux.dj/mm/vmscan.c
--- linux/mm/vmscan.c Mon Oct 2 20:02:20 2000
+++ linux.dj/mm/vmscan.c Wed Oct 11 23:46:01 2000
@@ -102,7 +102,9 @@
set_pte(page_table, swp_entry_to_pte(entry));
drop_pte:
UnlockPage(page);
+ spin_lock (&mm->page_table_lock);
mm->rss--;
+ spin_unlock (&mm->page_table_lock);
flush_tlb_page(vma, address);
deactivate_page(page);
page_cache_release(page);
@@ -170,7 +172,9 @@
struct file *file = vma->vm_file;
if (file) get_file(file);
pte_clear(page_table);
+ spin_lock (&mm->page_table_lock);
mm->rss--;
+ spin_unlock (&mm->page_table_lock);
flush_tlb_page(vma, address);
vmlist_access_unlock(mm);
error = swapout(page, file);
@@ -202,7 +206,9 @@
add_to_swap_cache(page, entry);

/* Put the swap entry into the pte after the page is in swapcache */
+ spin_lock (&mm->page_table_lock);
mm->rss--;
+ spin_unlock (&mm->page_table_lock);
set_pte(page_table, swp_entry_to_pte(entry));
flush_tlb_page(vma, address);
vmlist_access_unlock(mm);