From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f181.google.com (mail-io0-f181.google.com [209.85.223.181]) by kanga.kvack.org (Postfix) with ESMTP id 1915F6B0005 for ; Sun, 17 Jan 2016 20:15:44 -0500 (EST) Received: by mail-io0-f181.google.com with SMTP id g73so342718248ioe.3 for ; Sun, 17 Jan 2016 17:15:44 -0800 (PST) Received: from lgeamrelo12.lge.com (LGEAMRELO12.lge.com. [156.147.23.52]) by mx.google.com with ESMTPS id pi9si22674019igb.76.2016.01.17.17.15.42 for (version=TLS1 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Sun, 17 Jan 2016 17:15:43 -0800 (PST) From: Junil Lee Subject: [PATCH v3] zsmalloc: fix migrate_zspage-zs_free race condition Date: Mon, 18 Jan 2016 10:15:32 +0900 Message-ID: <1453079732-44198-1-git-send-email-junil0814.lee@lge.com> MIME-Version: 1.0 Content-Type: text/plain Sender: owner-linux-mm@kvack.org List-ID: To: minchan@kernel.org, ngupta@vflare.org Cc: sergey.senozhatsky.work@gmail.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Junil Lee To prevent unlock at the not correct situation, tagging the new obj to assure lock in migrate_zspage() before right unlock path. Two functions are in race condition by tag which set 1 on last bit of obj, however unlock succrently when update new obj to handle before call unpin_tag() which is right unlock path. summarize this problem by call flow as below: CPU0 CPU1 migrate_zspage find_alloced_obj() trypin_tag() -- obj |= HANDLE_PIN_BIT obj_malloc() -- new obj is not set zs_free record_obj() -- unlock and break sync pin_tag() -- get lock unpin_tag() Before code make crash as below: Unable to handle kernel NULL pointer dereference at virtual address 00000000 CPU: 0 PID: 19001 Comm: CookieMonsterCl Tainted: PC is at get_zspage_mapping+0x0/0x24 LR is at obj_free.isra.22+0x64/0x128 Call trace: [] get_zspage_mapping+0x0/0x24 [] zs_free+0x88/0x114 [] zram_free_page+0x64/0xcc [] zram_slot_free_notify+0x90/0x108 [] swap_entry_free+0x278/0x294 [] free_swap_and_cache+0x38/0x11c [] unmap_single_vma+0x480/0x5c8 [] unmap_vmas+0x44/0x60 [] exit_mmap+0x50/0x110 [] mmput+0x58/0xe0 [] do_exit+0x320/0x8dc [] do_group_exit+0x44/0xa8 [] get_signal+0x538/0x580 [] do_signal+0x98/0x4b8 [] do_notify_resume+0x14/0x5c and for test, print obj value after pin_tag() in zs_free(). Sometimes obj is even number means break synchronization. After patched, crash is not occurred and obj is only odd number in same situation. Signed-off-by: Junil Lee --- mm/zsmalloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index e7414ce..0acfa20 100644 --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -1635,8 +1635,8 @@ static int migrate_zspage(struct zs_pool *pool, struct size_class *class, free_obj = obj_malloc(d_page, class, handle); zs_object_copy(free_obj, used_obj, class); index++; + /* This also effectively unpins the handle */ record_obj(handle, free_obj); - unpin_tag(handle); obj_free(pool, class, used_obj); } -- 2.6.2 -- 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