Re: Panic/lockup in z3fold_zpool_free

[Brian Foster]

On Thu, Sep 22, 2022 at 08:53:09AM +0200, Oleksandr Natalenko wrote:
> Hello.
> 
> Since 5.19 series, zswap went unstable for me under memory pressure, and
> occasionally I get the following:
> 
> ```
> watchdog: BUG: soft lockup - CPU#0 stuck for 10195s! [mariadbd:478]
> Modules linked in: netconsole joydev mousedev intel_agp psmouse pcspkr
> intel_gtt cfg80211 cirrus i2c_piix4 tun rfkill mac_hid nft_ct tcp_bbr2
> nft_chain_nat nf_tables nfnetlink nf_nat nf_conntrack nf_defrag_ipv6
> nf_defrag_ipv4 fuse qemu_fw_cfg ip_tables x_tables xfs libcrc32c
> crc32c_generic dm_crypt cbc encrypted_keys trusted asn1_encoder tee tpm
> rng_core dm_mod crct10dif_pclmul crc32_pclmul crc32c_intel
> ghash_clmulni_intel virtio_net aesni_intel serio_raw net_failover
> ata_generic virtio_balloon failover pata_acpi crypto_simd virtio_blk atkbd
> libps2 vivaldi_fmap virtio_pci cryptd virtio_pci_legacy_dev ata_piix
> virtio_pci_modern_dev i8042 floppy serio usbhid
> Unloaded tainted modules: intel_cstate():1 intel_uncore():1 pcc_cpufreq():1
> acpi_cpufreq():1
> CPU: 0 PID: 478 Comm: mariadbd Tainted: G             L    5.19.0-pf5 #1
> 12baccda8e49539e158b9dd97cbda6c7317d73af
> Hardware name: Red Hat KVM, BIOS 1.11.0-2.el7 04/01/2014
> RIP: 0010:z3fold_zpool_free+0x4c/0x5e0
> Code: 7c 24 08 48 89 04 24 0f 85 e0 00 00 00 48 89 f5 41 bd 00 00 00 80 48
> 83 e5 c0 48 83 c5 28 eb 0a 48 89 df e8 b6 8d 9f 00 f3 90 <48> 89 ef e8 bc 8b
> 9f 00 4d 8b 34 24 49 81 e6 00 f0 ff ff 49 8d 5e
> RSP: 0000:ffffbeadc0e87b68 EFLAGS: 00000202
> RAX: 0000000000000030 RBX: ffff99ac73d2c010 RCX: ffff99ac4e4ba380
> RDX: 0000665340000000 RSI: ffffe3b540000000 RDI: ffff99ac73d2c010
> RBP: ffff99ac55ef3a68 R08: ffff99ac422f0bf0 R09: 000000000000c60b
> R10: ffffffffffffffc0 R11: 0000000000000000 R12: ffff99ac55ef3a50
> R13: 0000000080000000 R14: ffff99ac73d2c000 R15: ffff99acf3d2c000
> FS:  00007f587fcd66c0(0000) GS:ffff99ac7ec00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f587ce8bec8 CR3: 0000000005b48006 CR4: 00000000000206f0
> Call Trace:
>  <TASK>
>  zswap_free_entry+0xb5/0x110
>  zswap_frontswap_invalidate_page+0x72/0xa0
>  __frontswap_invalidate_page+0x3a/0x60
>  swap_range_free+0xb5/0xd0
>  swapcache_free_entries+0x16e/0x2e0
>  free_swap_slot+0xb4/0xc0
>  put_swap_page+0x259/0x420
>  delete_from_swap_cache+0x63/0xb0
>  try_to_free_swap+0x1b5/0x2a0
>  do_swap_page+0x24c/0xb80
>  __handle_mm_fault+0xa59/0xf70
>  handle_mm_fault+0x100/0x2f0
>  do_user_addr_fault+0x1c7/0x6a0
>  exc_page_fault+0x74/0x170
>  asm_exc_page_fault+0x26/0x30
> RIP: 0033:0x556e96280428
> Code: a0 03 00 00 67 e8 28 64 ff ff 48 8b 83 b0 00 00 00 48 8b 0d da 18 72
> 00 48 8b 10 66 48 0f 6e c1 48 85 d2 74 27 0f 1f 44 00 00 <48> c7 82 98 00 00
> 00 00 00 00 00 48 8b 10 48 83 c0 08 f2 0f 11 82
> RSP: 002b:00007f587fcd3980 EFLAGS: 00010206
> RAX: 00007f587d028468 RBX: 00007f587cb1a818 RCX: 3ff0000000000000
> RDX: 00007f587ce8be30 RSI: 0000000000000000 RDI: 00007f587cedd030
> RBP: 00007f587fcd39c0 R08: 0000000000000016 R09: 0000000000000000
> R10: 0000000000000008 R11: 0000556e970961a0 R12: 00007f587d1f17b8
> R13: 00007f5883595598 R14: 00007f587d1f17a8 R15: 00007f587cb1a928
>  </TASK>
> ```
> 
> This happens on the latest v5.19.10 kernel as well.
> 
> Sometimes it's not a soft lockup but GPF, although the stack trace is the
> same. So, to me it looks like a memory corruption, UAF, double free or
> something like that.
> 
> Have you got any idea regarding what's going on?
> 

It might be unrelated, but this looks somewhat similar to a problem I
hit recently that is caused by swap entry data stored in page->private
being clobbered when splitting a huge page. That problem was introduced
in v5.19, so that potentially lines up as well.

More details in the links below. [1] includes a VM_BUG_ON() splat with
DEBUG_VM enabled, but the problem originally manifested as a soft lockup
without the debug checks enabled. [2] includes a properly formatted
patch. Any chance you could give that a try?

Brian

[1] https://lore.kernel.org/linux-mm/YxDyZLfBdFHK1Y1P@bfoster/
[2] https://lore.kernel.org/linux-mm/20220906190602.1626037-1-bfoster@xxxxxxxxxx/

> Thanks.
> 
> -- 
>   Oleksandr Natalenko (post-factum)
>