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[23.128.96.18]) by mx.google.com with ESMTP id p13si12825793edt.516.2021.03.29.01.34.38; Mon, 29 Mar 2021 01:35:01 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@linuxfoundation.org header.s=korg header.b=LDLAbApJ; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=linuxfoundation.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232209AbhC2Idn (ORCPT + 99 others); Mon, 29 Mar 2021 04:33:43 -0400 Received: from mail.kernel.org ([198.145.29.99]:37864 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233440AbhC2IU5 (ORCPT ); Mon, 29 Mar 2021 04:20:57 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id DCF3A6197C; Mon, 29 Mar 2021 08:20:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1617006057; bh=MbL7AKpdxRzYn7bkW1NYv6bd4nhHz27ETGLC75e+OLY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=LDLAbApJo4qBKkHKLOlHQ1LbjOZu5YDgO49wnyhXj659WdgpM0j5v67MpoKGtCidd d4Q7Vg5o58lGLAuetGQOYnnpnlOQ5ImJtBfK1RknTwrtjbPFHX7HjYl1lMlr+QS6kD eiZoZ3BzcE3htoR1g8HkvIgYPmfEv7rtF1BlbnYg= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Thomas Hebb , Vitaly Wool , Jongseok Kim , Snild Dolkow , Andrew Morton , Linus Torvalds Subject: [PATCH 5.10 068/221] z3fold: prevent reclaim/free race for headless pages Date: Mon, 29 Mar 2021 09:56:39 +0200 Message-Id: <20210329075631.445196329@linuxfoundation.org> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210329075629.172032742@linuxfoundation.org> References: <20210329075629.172032742@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Thomas Hebb commit 6d679578fe9c762c8fbc3d796a067cbba84a7884 upstream. 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 dcf5aedb24f8 ("z3fold: stricter locking and more careful reclaim") appears to have unintentionally broken this behavior by moving 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:0000000000000000 index:0x0 pfn:0x165316 flags: 0x2ffff0000000000() raw: 02ffff0000000000 ffffea0004535f48 ffff8881d553a170 0000000000000000 raw: 0000000000000000 0000000000000011 00000000ffffffff 0000000000000000 page dumped because: VM_BUG_ON_PAGE(page_ref_count(page) == 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:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f7c8c3654d8 CR3: 0000000103f42004 CR4: 00000000001706e0 Call Trace: z3fold_zpool_shrink+0x9b6/0x1240 shrink_worker+0x35/0x90 process_one_work+0x70c/0x1210 worker_thread+0x539/0x1200 kthread+0x330/0x400 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_skcipher cmac bnep md4 algif_hash af_alg vfat fat intel_rapl_msr intel_rapl_common x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel iwlmvm hid_logitech_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 irqbypass iwlwifi soundwire_generic_allocation rapl soundwire_cadence intel_cstate snd_hda_codec intel_uncore btusb joydev mousedev snd_usb_audio pcspkr btrtl uvcvideo nouveau btbcm i2c_i801 btintel snd_hda_core videobuf2_vmalloc 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_generic 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 pkcs8_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_core usbhid dm_mod crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel aesni_intel crypto_simd cryptd glue_helper xhci_pci xhci_pci_renesas i915 video intel_gtt i2c_algo_bit drm_kms_helper syscopyarea sysfillrect sysimgblt 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. Link: https://lkml.kernel.org/r/c8106dbe6d8390b290cd1d7f873a2942e805349e.1615452048.git.tommyhebb@gmail.com Fixes: dcf5aedb24f8 ("z3fold: stricter locking and more careful reclaim") Signed-off-by: Thomas Hebb Reviewed-by: Vitaly Wool Cc: Jongseok Kim Cc: Snild Dolkow Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/z3fold.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) --- a/mm/z3fold.c +++ b/mm/z3fold.c @@ -1350,8 +1350,22 @@ static int z3fold_reclaim_page(struct z3 page = list_entry(pos, struct page, lru); zhdr = page_address(page); - if (test_bit(PAGE_HEADLESS, &page->private)) + if (test_bit(PAGE_HEADLESS, &page->private)) { + /* + * For non-headless pages, we wait to do this + * until we have the page lock to avoid racing + * with __z3fold_alloc(). Headless pages don't + * have a lock (and __z3fold_alloc() will never + * see them), but we still need to test and set + * PAGE_CLAIMED to avoid racing with + * z3fold_free(), so just do it now before + * leaving the loop. + */ + if (test_and_set_bit(PAGE_CLAIMED, &page->private)) + continue; + break; + } if (kref_get_unless_zero(&zhdr->refcount) == 0) { zhdr = NULL;