From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f50.google.com (mail-pa0-f50.google.com [209.85.220.50]) by kanga.kvack.org (Postfix) with ESMTP id 0983F6B0031 for ; Sun, 13 Oct 2013 17:12:49 -0400 (EDT) Received: by mail-pa0-f50.google.com with SMTP id fb1so6730740pad.37 for ; Sun, 13 Oct 2013 14:12:49 -0700 (PDT) Received: by mail-oa0-f46.google.com with SMTP id o1so501161oag.19 for ; Sun, 13 Oct 2013 14:12:47 -0700 (PDT) MIME-Version: 1.0 Date: Mon, 14 Oct 2013 01:12:47 +0400 Message-ID: Subject: CONFIG_SLUB/USE_SPLIT_PTLOCKS compatibility From: Max Filippov Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: LKML , "linux-mm@kvack.org" , Christoph Lameter , Pekka Enberg , Matt Mackall Hello, I'm reliably getting kernel crash on xtensa when CONFIG_SLUB is selected and USE_SPLIT_PTLOCKS appears to be true (SMP=y, NR_CPUS=4, DEBUG_SPINLOCK=n, DEBUG_LOCK_ALLOC=n). This happens because spinlock_t ptl and struct page *first_page overlap in the struct page. The following call chain makes allocation of order 3 and initializes first_page pointer in its 7 tail pages: do_page_fault handle_mm_fault __pte_alloc kmem_cache_alloc __slab_alloc new_slab __alloc_pages_nodemask get_page_from_freelist prep_compound_page Later pte_offset_map_lock is called with one of these tail pages overwriting its first_page pointer: do_fork copy_process dup_mm copy_page_range copy_pte_range pte_alloc_map_lock pte_offset_map_lock Finally kmem_cache_free is called for that tail page, which calls slab_free(s, virt_to_head_page(x),... but virt_to_head_page here returns NULL, because the page's first_page pointer was overwritten earlier: exit_mmap free_pgtables free_pgd_range free_pud_range free_pmd_range free_pte_range pte_free kmem_cache_free slab_free __slab_free __slab_free touches NULL struct page, that's it. Changing allocator to SLAB or enabling DEBUG_SPINLOCK fixes that crash. My question is, is CONFIG_SLUB supposed to work with USE_SPLIT_PTLOCKS (and if yes what's wrong in my case)? -- Thanks. -- Max -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org