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authorThomas Hebb <tommyhebb@gmail.com>2021-03-24 21:37:29 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2021-03-25 09:22:55 -0700
commit6d679578fe9c762c8fbc3d796a067cbba84a7884 (patch)
tree2291a44f1058b6a27c4e5935836cb1ce8a714437 /mm
parent19ec368cbc7ee1915e78c120b7a49c7f14734192 (diff)
z3fold: prevent reclaim/free race for headless pages
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 <tommyhebb@gmail.com> Reviewed-by: Vitaly Wool <vitaly.wool@konsulko.com> Cc: Jongseok Kim <ks77sj@gmail.com> Cc: Snild Dolkow <snild@sony.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/z3fold.c16
1 files changed, 15 insertions, 1 deletions
diff --git a/mm/z3fold.c b/mm/z3fold.c
index b5dafa7e44e4..9d889ad2bb86 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -1346,8 +1346,22 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
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;