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

From: Rasmus Andersen (rasmus@jaquet.dk)
Date: Sat Nov 04 2000 - 18:37:08 EST


On Fri, Nov 03, 2000 at 06:51:05AM -0800, David S. Miller wrote:
> Are you saying that the original bug report may not actually be a
> problem? Is ms->rss actually protected in _all_ of the right
> places, but people got confused because of the syntactic sugar?
>
> I don't know if all of them are ok, most are.
>

Would this do? This is a subset of Davej's patch. I also noted that
fs/{exec.c,binfmt_aout.c,binfmt_elf.c} modifies rss without holding
the lock. I think exec.c needs it, but am at a loss whether the
binfmt_* does too. The second patch below adds the lock to fs/exec.c.

Comments?

diff -ura linux-240-t10-clean/mm/memory.c linux/mm/memory.c
--- linux-240-t10-clean/mm/memory.c Sat Nov 4 23:27:17 2000
+++ linux/mm/memory.c Sun Nov 5 00:13:59 2000
@@ -369,7 +369,6 @@
                 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.
@@ -378,6 +377,7 @@
                 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 -ura linux-240-t10-clean/mm/mmap.c linux/mm/mmap.c
--- linux-240-t10-clean/mm/mmap.c Sat Nov 4 23:27:17 2000
+++ linux/mm/mmap.c Sat Nov 4 23:53:49 2000
@@ -843,8 +843,8 @@
         spin_lock(&mm->page_table_lock);
         mpnt = mm->mmap;
         mm->mmap = mm->mmap_avl = mm->mmap_cache = NULL;
- spin_unlock(&mm->page_table_lock);
         mm->rss = 0;
+ spin_unlock(&mm->page_table_lock);
         mm->total_vm = 0;
         mm->locked_vm = 0;
         while (mpnt) {
diff -ura linux-240-t10-clean/mm/swapfile.c linux/mm/swapfile.c
--- linux-240-t10-clean/mm/swapfile.c Sat Nov 4 23:27:17 2000
+++ linux/mm/swapfile.c Sun Nov 5 00:19:15 2000
@@ -231,7 +231,9 @@
         set_pte(dir, pte_mkdirty(mk_pte(page, vma->vm_page_prot)));
         swap_free(entry);
         get_page(page);
+ spin_lock(&vma->vm_mm->page_table_lock);
         ++vma->vm_mm->rss;
+ spin_unlock(&vma->vm_mm->page_table_lock);
 }
 
 static inline void unuse_pmd(struct vm_area_struct * vma, pmd_t *dir,
diff -ura linux-240-t10-clean/mm/vmscan.c linux/mm/vmscan.c
--- linux-240-t10-clean/mm/vmscan.c Sat Nov 4 23:27:17 2000
+++ linux/mm/vmscan.c Sun Nov 5 00:19:48 2000
@@ -95,7 +95,9 @@
                 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);

Second patch:

--- linux-240-t10-clean/fs/exec.c Sat Nov 4 23:27:14 2000
+++ linux/fs/exec.c Sat Nov 4 23:55:37 2000
@@ -324,7 +324,9 @@
                 struct page *page = bprm->page[i];
                 if (page) {
                         bprm->page[i] = NULL;
+ spin_lock(mm->page_table_lock);
                         current->mm->rss++;
+ spin_unlock(mm->page_table_lock);
                         put_dirty_page(current,page,stack_base);
                 }
                 stack_base += PAGE_SIZE;

-- 
Regards,
        Rasmus(rasmus@jaquet.dk)

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