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([2601:647:6000:3e5b::a27]) by smtp.gmail.com with ESMTPSA id c22sm1585829pfl.169.2021.03.11.00.40.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 11 Mar 2021 00:40:57 -0800 (PST) From: Thomas Hebb To: linux-kernel@vger.kernel.org Cc: Thomas Hebb , stable@vger.kernel.org, Andrew Morton , Vitaly Wool , linux-mm@kvack.org Subject: [PATCH] z3fold: prevent reclaim/free race for headless pages Date: Thu, 11 Mar 2021 00:40:54 -0800 Message-Id: X-Mailer: git-send-email 2.30.0 MIME-Version: 1.0 X-Stat-Signature: ko6dw9jhh7bo5894j49e7u3xdho4snya X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 8E9D5407F8FE Received-SPF: none (gmail.com>: No applicable sender policy available) receiver=imf26; identity=mailfrom; envelope-from=""; helo=mail-pl1-f182.google.com; client-ip=209.85.214.182 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1615452056-330336 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 0000000000000= 000 raw: 0000000000000000 0000000000000011 00000000ffffffff 0000000000000= 000 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, BIO= S 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:000000000= 0000000 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_skciph= er 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_l= ogitech_hidpp kvm at24 mac80211 snd_hda_codec_realtek iTCO_wdt snd_hda_co= dec_generic intel_pmc_bxt snd_hda_codec_hdmi ledtrig_audio iTCO_vendor_su= pport mei_wdt mei_hdcp snd_hda_intel snd_intel_dspcfg libarc4 soundwire_i= ntel irqbypass iwlwifi soundwire_generic_allocation rapl soundwire_cadenc= e intel_cstate snd_hda_codec intel_uncore btusb joydev mousedev snd_usb_a= udio pcspkr btrtl uvcvideo nouveau btbcm i2c_i801 btintel snd_hda_core vi= deobuf2_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 sn= d_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_c= ore usbhid dm_mod crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmuln= i_intel aesni_intel crypto_simd cryptd glue_helper xhci_pci xhci_pci_rene= sas i915 video intel_gtt i2c_algo_bit drm_kms_helper syscopyarea sysfillr= ect 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. Fixes: dcf5aedb24f8 ("z3fold: stricter locking and more careful reclaim") Cc: stable@vger.kernel.org Signed-off-by: Thomas Hebb --- mm/z3fold.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/mm/z3fold.c b/mm/z3fold.c index 0152ad9931a8..8ae944eeb8e2 100644 --- a/mm/z3fold.c +++ b/mm/z3fold.c @@ -1350,8 +1350,22 @@ static int z3fold_reclaim_page(struct z3fold_pool = *pool, unsigned int retries) page =3D list_entry(pos, struct page, lru); =20 zhdr =3D 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; + } =20 if (kref_get_unless_zero(&zhdr->refcount) =3D=3D 0) { zhdr =3D NULL; --=20 2.30.0