Messages in this thread Patch in this message |  | | Date | Fri, 3 Nov 2000 06:39:22 -0500 | Subject | BUG FIX?: mm->rss is modified in some places without holding the page_table_lock | From | tytso@mit ... |
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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);
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