From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f173.google.com (mail-pf0-f173.google.com [209.85.192.173]) by kanga.kvack.org (Postfix) with ESMTP id EC0BC6B0005 for ; Mon, 18 Jan 2016 01:12:32 -0500 (EST) Received: by mail-pf0-f173.google.com with SMTP id n128so152223132pfn.3 for ; Sun, 17 Jan 2016 22:12:32 -0800 (PST) Received: from mail-pf0-x244.google.com (mail-pf0-x244.google.com. [2607:f8b0:400e:c00::244]) by mx.google.com with ESMTPS id 11si29475559pfn.64.2016.01.17.22.12.32 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 17 Jan 2016 22:12:32 -0800 (PST) Received: by mail-pf0-x244.google.com with SMTP id 65so11308991pfd.1 for ; Sun, 17 Jan 2016 22:12:32 -0800 (PST) Date: Mon, 18 Jan 2016 15:13:43 +0900 From: Sergey Senozhatsky Subject: Re: [PATCH v3] zsmalloc: fix migrate_zspage-zs_free race condition Message-ID: <20160118061343.GA459@swordfish> References: <1453095596-44055-1-git-send-email-junil0814.lee@lge.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1453095596-44055-1-git-send-email-junil0814.lee@lge.com> Sender: owner-linux-mm@kvack.org List-ID: To: Junil Lee Cc: minchan@kernel.org, ngupta@vflare.org, sergey.senozhatsky.work@gmail.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, vbabka@suse.cz On (01/18/16 14:39), Junil Lee wrote: > record_obj() in migrate_zspage() does not preserve handle's > HANDLE_PIN_BIT, set by find_aloced_obj()->trypin_tag(), and implicitly > (accidentally) un-pins the handle, while migrate_zspage() still performs > an explicit unpin_tag() on the that handle. > This additional explicit unpin_tag() introduces a race condition with > zs_free(), which can pin that handle by this time, so the handle becomes > un-pinned. > > Schematically, it goes like this: > > CPU0 CPU1 > migrate_zspage > find_alloced_obj > trypin_tag > set HANDLE_PIN_BIT zs_free() > pin_tag() > obj_malloc() -- new object, no tag > record_obj() -- remove HANDLE_PIN_BIT set HANDLE_PIN_BIT > unpin_tag() -- remove zs_free's HANDLE_PIN_BIT > > The race condition may result in a NULL pointer dereference: > 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 > > Fix the race by removing explicit unpin_tag() from migrate_zspage(). > > Signed-off-by: Junil Lee Suggested-by: Vlastimil Babka Acked-by: Sergey Senozhatsky Cc: [4.1+] migrate_zspage() was introduced in 4.1 https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/mm/zsmalloc.c?id=refs/tags/v4.1 thank you. -ss > --- > 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