From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DC76DC433E0 for ; Tue, 16 Feb 2021 10:14:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8B6FD64DCF for ; Tue, 16 Feb 2021 10:14:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229954AbhBPKOP (ORCPT ); Tue, 16 Feb 2021 05:14:15 -0500 Received: from mail.kernel.org ([198.145.29.99]:55912 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229916AbhBPKOJ (ORCPT ); Tue, 16 Feb 2021 05:14:09 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 94C6464D9E; Tue, 16 Feb 2021 10:13:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1613470407; bh=Vaq2d2GeS1UR7VX8wZLz66q1a0W5YZnKnzsmvxYNvlw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=XFkcLkW0Rd9c6FSgAQx8ECPrQQzBiJHUDePykPhGZz3vsRMmI4s+ieFqfaFdS6HLY kf9uxTvPKbo1vdFBfN81rmlldu6gqCFiHee3S1+ZfLnd7N50NBYwEz/Ecq3ySfdSwO hGTNB6hQd3dwoQy056AEwsn/kh0ycl8I8wS3Lrgs= Date: Tue, 16 Feb 2021 11:13:24 +0100 From: Greg Kroah-Hartman To: Tom Hebb Cc: linux-kernel@vger.kernel.org, Andrew Morton , Vitaly Wool , linux-mm@kvack.org Subject: Re: [RFC PATCH] z3fold: prevent reclaim/free race for headless pages Message-ID: References: <8c4f1cb7c51b03d2b2cd451a6404db8e269d94b7.1613465062.git.tommyhebb@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 16, 2021 at 02:04:20AM -0800, Tom Hebb wrote: > On Tue, Feb 16, 2021 at 1:21 AM Greg Kroah-Hartman > wrote: > > > > On Tue, Feb 16, 2021 at 12:44:40AM -0800, Thomas Hebb wrote: > > > commit ca0246bb97c2 ("z3fold: fix possible reclaim races") introduced > > > the PAGE_CLAIMED flag "to avoid racing on a z3fold 'headless' page > > > release." By atomically testing and setting the bit in each of > > > z3fold_free() and z3fold_reclaim_page(), a double-free was avoided. > > > > > > However, commit 746d179b0e66 ("z3fold: stricter locking and more care= ful > > > reclaim") appears to have unintentionally broken this behavior by mov= ing > > > the PAGE_CLAIMED check in z3fold_reclaim_page() to after the page lock > > > gets taken, which only happens for non-headless pages. For headless > > > pages, the check is now skipped entirely and races can occur again. > > > > > > I have observed such a race on my system: > > > > > > page:00000000ffbd76b7 refcount:0 mapcount:0 mapping:0000000000000= 000 index:0x0 pfn:0x165316 > > > flags: 0x2ffff0000000000() > > > raw: 02ffff0000000000 ffffea0004535f48 ffff8881d553a170 000000000= 0000000 > > > raw: 0000000000000000 0000000000000011 00000000ffffffff 000000000= 0000000 > > > page dumped because: VM_BUG_ON_PAGE(page_ref_count(page) =3D=3D 0) > > > ------------[ cut here ]------------ > > > kernel BUG at include/linux/mm.h:707! > > > invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI > > > CPU: 2 PID: 291928 Comm: kworker/2:0 Tainted: G B = 5.10.7-arch1-1-kasan #1 > > > Hardware name: Gigabyte Technology Co., Ltd. H97N-WIFI/H97N-WIFI,= BIOS F9b 03/03/2016 > > > Workqueue: zswap-shrink shrink_worker > > > RIP: 0010:__free_pages+0x10a/0x130 > > > Code: c1 e7 06 48 01 ef 45 85 e4 74 d1 44 89 e6 31 d2 41 83 ec 01= e8 e7 b0 ff ff eb da 48 c7 c6 e0 32 91 88 48 89 ef e8 a6 89 f8 ff <0f> 0b = 4c 89 e7 e8 fc 79 07 00 e9 33 ff ff ff 48 89 ef e8 ff 79 07 > > > RSP: 0000:ffff88819a2ffb98 EFLAGS: 00010296 > > > RAX: 0000000000000000 RBX: ffffea000594c5a8 RCX: 0000000000000000 > > > RDX: 1ffffd4000b298b7 RSI: 0000000000000000 RDI: ffffea000594c5b8 > > > RBP: ffffea000594c580 R08: 000000000000003e R09: ffff8881d5520bbb > > > R10: ffffed103aaa4177 R11: 0000000000000001 R12: ffffea000594c5b4 > > > R13: 0000000000000000 R14: ffff888165316000 R15: ffffea000594c588 > > > FS: 0000000000000000(0000) GS:ffff8881d5500000(0000) knlGS:00000= 00000000000 > > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > > CR2: 00007f7c8c3654d8 CR3: 0000000103f42004 CR4: 00000000001706e0 > > > Call Trace: > > > z3fold_zpool_shrink+0x9b6/0x1240 > > > ? sugov_update_single+0x357/0x990 > > > ? sched_clock+0x5/0x10 > > > ? sched_clock_cpu+0x18/0x180 > > > ? z3fold_zpool_map+0x490/0x490 > > > ? _raw_spin_lock_irq+0x88/0xe0 > > > shrink_worker+0x35/0x90 > > > process_one_work+0x70c/0x1210 > > > ? pwq_dec_nr_in_flight+0x15b/0x2a0 > > > worker_thread+0x539/0x1200 > > > ? __kthread_parkme+0x73/0x120 > > > ? rescuer_thread+0x1000/0x1000 > > > kthread+0x330/0x400 > > > ? __kthread_bind_mask+0x90/0x90 > > > ret_from_fork+0x22/0x30 > > > Modules linked in: rfcomm ebtable_filter ebtables ip6table_filter= ip6_tables iptable_filter ccm algif_aead des_generic libdes ecb algif_skci= pher cmac bnep md4 algif_hash af_alg vfat fat intel_rapl_msr intel_rapl_com= mon x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel iwlmvm hid_log= itech_hidpp kvm at24 mac80211 snd_hda_codec_realtek iTCO_wdt snd_hda_codec_= generic intel_pmc_bxt snd_hda_codec_hdmi ledtrig_audio iTCO_vendor_support = mei_wdt mei_hdcp snd_hda_intel snd_intel_dspcfg libarc4 soundwire_intel irq= bypass iwlwifi soundwire_generic_allocation rapl soundwire_cadence intel_cs= tate snd_hda_codec intel_uncore btusb joydev mousedev snd_usb_audio pcspkr = btrtl uvcvideo nouveau btbcm i2c_i801 btintel snd_hda_core videobuf2_vmallo= c i2c_smbus snd_usbmidi_lib videobuf2_memops bluetooth snd_hwdep soundwire_= bus snd_soc_rt5640 videobuf2_v4l2 cfg80211 snd_soc_rl6231 videobuf2_common = snd_rawmidi lpc_ich alx videodev mdio snd_seq_device snd_soc_core mc ecdh_g= eneric mxm_wmi mei_me > > > hid_logitech_dj wmi snd_compress e1000e ac97_bus mei ttm rfkill = snd_pcm_dmaengine ecc snd_pcm snd_timer snd soundcore mac_hid acpi_pad pkcs= 8_key_parser it87 hwmon_vid crypto_user fuse ip_tables x_tables ext4 crc32c= _generic crc16 mbcache jbd2 dm_crypt cbc encrypted_keys trusted tpm rng_cor= e usbhid dm_mod crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_in= tel aesni_intel crypto_simd cryptd glue_helper xhci_pci xhci_pci_renesas i9= 15 video intel_gtt i2c_algo_bit drm_kms_helper syscopyarea sysfillrect sysi= mgblt fb_sys_fops cec drm agpgart > > > ---[ end trace 126d646fc3dc0ad8 ]--- > > > > > > To fix the issue, re-add the earlier test and set in the case where we > > > have a headless page. > > > > > > Fixes: 746d179b0e66 ("z3fold: stricter locking and more careful recla= im") > > > > This commit id is not in Linus's tree :( >=20 > Oops, I was building from a 5.10 stable tree and accidentally grabbed > the ID of the pick there. This is the correct line, will fix in v1: >=20 > Fixes: dcf5aedb24f8 ("z3fold: stricter locking and more careful reclaim") Great. Also can you add a "cc: stable@vger.kernel.org" line as well to the signed-off-by area so that the patch automatically will get backported to the proper stable kernels that are affected? thanks, greg k-h