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author | Thomas Hebb <tommyhebb@gmail.com> | 2021-03-25 07:37:29 +0300 |
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committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-03-30 15:31:54 +0300 |
commit | 1d215fcbc4ef305614871bbb2399f7b4670cb266 (patch) | |
tree | 4e365c17dee1ea61c19e4e3e5c676f0a92513a33 /mm | |
parent | e4642090734e63017f02e14dfbdd41164b9e4783 (diff) | |
download | linux-1d215fcbc4ef305614871bbb2399f7b4670cb266.tar.xz |
z3fold: prevent reclaim/free race for headless pages
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 <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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'mm')
-rw-r--r-- | mm/z3fold.c | 16 |
1 files changed, 15 insertions, 1 deletions
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 = 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; |