Re: WARNING at asm/kfence.h:44 kfence_protect_page

[Chris Murphy <lists@colorremedies.com>]

On Mon, Jun 14, 2021 at 11:50 AM Filipe Manana <fdmanana@gmail.com> wrote:
>
> On Mon, Jun 14, 2021 at 6:05 PM Chris Murphy <lists@colorremedies.com> wrote:
> >
> > 5.12.9-300.fc34.x86_64
> >
> > File system is btrfs, 16G RAM, 8G /dev/zram0 is used for swap, and the
> > workload is:
> > * bees doing dedup
> > * btrfs send
> > * digikam scanning files and writing image metadata to a sqlite database
> > * chrome doing some webby things
> >
> > And then kaboom.
> >
> > Call trace (easy to read, expires in 7 days):
> > https://pastebin.com/x5KRU23V
> >
> > Same call trace (MUA mangled, for the archive):
> > [60015.902283] kernel: WARNING: CPU: 3 PID: 58159 at
> > arch/x86/include/asm/kfence.h:44 kfence_protect_page+0x21/0x80
> > [60015.902292] kernel: Modules linked in: uinput rfcomm snd_seq_dummy
> > snd_hrtimer xt_CHECKSUM xt_MASQUERADE xt_conntrack ipt_REJECT
> > nf_nat_tftp nf_conntrack_tftp nft_objref nf_conntrack_netbios_ns
> > nf_conntrack_broadcast nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib
> > 8021q garp mrp nft_reject_inet nf_reject_ipv4 nf_reject_ipv6
> > nft_reject bridge stp llc nft_ct nft_chain_nat ip6table_nat
> > ip6table_mangle ip6table_raw ip6table_security iptable_nat nf_nat
> > nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 iptable_mangle iptable_raw
> > iptable_security ip_set nf_tables nfnetlink ip6table_filter ip6_tables
> > iptable_filter cmac bnep sunrpc vfat fat iwldvm mac80211 btusb btrtl
> > edac_mce_amd libarc4 btbcm snd_hda_codec_realtek iwlwifi
> > snd_hda_codec_generic ledtrig_audio btintel snd_hda_codec_hdmi
> > snd_hda_intel bluetooth kvm_amd snd_intel_dspcfg cfg80211
> > snd_intel_sdw_acpi ccp snd_hda_codec snd_hda_core kvm snd_hwdep
> > snd_seq joydev irqbypass snd_seq_device snd_pcm ecdh_generic ecc
> > k10temp rfkill i2c_piix4 fam15h_power
> > [60015.902361] kernel:  pcspkr snd_timer snd r8169 soundcore
> > acpi_cpufreq zram ip_tables amdgpu iommu_v2 gpu_sched crct10dif_pclmul
> > crc32_pclmul crc32c_intel radeon ghash_clmulni_intel sp5100_tco
> > i2c_algo_bit drm_ttm_helper ttm drm_kms_helper cec drm video fuse
> > [60015.902384] kernel: CPU: 3 PID: 58159 Comm: btrfs Not tainted
> > 5.12.9-300.fc34.x86_64 #1
> > [60015.902387] kernel: Hardware name: Gigabyte Technology Co., Ltd. To
> > be filled by O.E.M./F2A88XN-WIFI, BIOS F6 12/24/2015
> > [60015.902389] kernel: RIP: 0010:kfence_protect_page+0x21/0x80
> > [60015.902393] kernel: Code: ff 0f 1f 84 00 00 00 00 00 55 48 89 fd 53
> > 89 f3 48 83 ec 08 48 8d 74 24 04 e8 cb e0 d7 ff 48 85 c0 74 07 83 7c
> > 24 04 01 74 0b <0f> 0b 48 83 c4 08 31 c0 5b 5d c3 48 8b 38 48 89 c2 84
> > db 75 36 48
> > [60015.902396] kernel: RSP: 0018:ffff9fb583453220 EFLAGS: 00010246
> > [60015.902399] kernel: RAX: 0000000000000000 RBX: 0000000000000000
> > RCX: ffff9fb583453224
> > [60015.902401] kernel: RDX: ffff9fb583453224 RSI: 0000000000000000
> > RDI: 0000000000000000
> > [60015.902402] kernel: RBP: 0000000000000000 R08: 0000000000000000
> > R09: 0000000000000000
> > [60015.902404] kernel: R10: 0000000000000000 R11: 0000000000000000
> > R12: 0000000000000002
> > [60015.902406] kernel: R13: ffff9fb583453348 R14: 0000000000000000
> > R15: 0000000000000001
> > [60015.902408] kernel: FS:  00007f158e62d8c0(0000)
> > GS:ffff93bd37580000(0000) knlGS:0000000000000000
> > [60015.902410] kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [60015.902412] kernel: CR2: 0000000000000039 CR3: 00000001256d2000
> > CR4: 00000000000506e0
> > [60015.902414] kernel: Call Trace:
> > [60015.902419] kernel:  kfence_unprotect+0x13/0x30
> > [60015.902423] kernel:  page_fault_oops+0x89/0x270
> > [60015.902427] kernel:  ? search_module_extables+0xf/0x40
> > [60015.902431] kernel:  ? search_bpf_extables+0x57/0x70
> > [60015.902435] kernel:  kernelmode_fixup_or_oops+0xd6/0xf0
> > [60015.902437] kernel:  __bad_area_nosemaphore+0x142/0x180
> > [60015.902440] kernel:  exc_page_fault+0x67/0x150
> > [60015.902445] kernel:  asm_exc_page_fault+0x1e/0x30
> > [60015.902450] kernel: RIP: 0010:start_transaction+0x71/0x580
> > [60015.902454] kernel: Code: d3 0f 84 92 00 00 00 80 e7 06 0f 85 63 04
> > 00 00 65 48 8b 04 25 c0 7b 01 00 4c 8b a0 70 0c 00 00 b8 01 00 00 00
> > 49 8d 7c 24 38 <f0> 41 0f c1 44 24 38 85 c0 0f 84 41 04 00 00 8d 50 01
> > 09 c2 0f 88
> > [60015.902456] kernel: RSP: 0018:ffff9fb5834533f8 EFLAGS: 00010246
> > [60015.902458] kernel: RAX: 0000000000000001 RBX: 0000000000000001
> > RCX: 0000000000000000
> > [60015.902460] kernel: RDX: 0000000000000801 RSI: 0000000000000000
> > RDI: 0000000000000039
> > [60015.902462] kernel: RBP: ffff93bc0a7eb800 R08: 0000000000000001
> > R09: 0000000000000000
> > [60015.902463] kernel: R10: 0000000000098a00 R11: 0000000000000001
> > R12: 0000000000000001
> > [60015.902464] kernel: R13: 0000000000000000 R14: ffff93bc0c92b000
> > R15: ffff93bc0c92b000
> > [60015.902468] kernel:  btrfs_commit_inode_delayed_inode+0x5d/0x120
> > [60015.902473] kernel:  btrfs_evict_inode+0x2c5/0x3f0
> > [60015.902476] kernel:  evict+0xd1/0x180
> > [60015.902480] kernel:  inode_lru_isolate+0xe7/0x180
> > [60015.902483] kernel:  __list_lru_walk_one+0x77/0x150
> > [60015.902487] kernel:  ? iput+0x1a0/0x1a0
> > [60015.902489] kernel:  ? iput+0x1a0/0x1a0
> > [60015.902491] kernel:  list_lru_walk_one+0x47/0x70
> > [60015.902495] kernel:  prune_icache_sb+0x39/0x50
> > [60015.902497] kernel:  super_cache_scan+0x161/0x1f0
> > [60015.902501] kernel:  do_shrink_slab+0x142/0x240
> > [60015.902505] kernel:  shrink_slab+0x164/0x280
> > [60015.902509] kernel:  shrink_node+0x2c8/0x6e0
> > [60015.902512] kernel:  do_try_to_free_pages+0xcb/0x4b0
> > [60015.902514] kernel:  try_to_free_pages+0xda/0x190
> > [60015.902516] kernel:  __alloc_pages_slowpath.constprop.0+0x373/0xcc0
> > [60015.902521] kernel:  ? __memcg_kmem_charge_page+0xc2/0x1e0
> > [60015.902525] kernel:  __alloc_pages_nodemask+0x30a/0x340
> > [60015.902528] kernel:  pipe_write+0x30b/0x5c0
> > [60015.902531] kernel:  ? set_next_entity+0xad/0x1e0
> > [60015.902534] kernel:  ? switch_mm_irqs_off+0x58/0x440
> > [60015.902538] kernel:  __kernel_write+0x13a/0x2b0
> > [60015.902541] kernel:  kernel_write+0x73/0x150
> > [60015.902543] kernel:  send_cmd+0x7b/0xd0
> > [60015.902545] kernel:  send_extent_data+0x5a3/0x6b0
> > [60015.902549] kernel:  process_extent+0x19b/0xed0
> > [60015.902551] kernel:  btrfs_ioctl_send+0x1434/0x17e0
> > [60015.902554] kernel:  ? _btrfs_ioctl_send+0xe1/0x100
> > [60015.902557] kernel:  _btrfs_ioctl_send+0xbf/0x100
> > [60015.902559] kernel:  ? enqueue_entity+0x18c/0x7b0
> > [60015.902562] kernel:  btrfs_ioctl+0x185f/0x2f80
> > [60015.902564] kernel:  ? psi_task_change+0x84/0xc0
> > [60015.902569] kernel:  ? _flat_send_IPI_mask+0x21/0x40
> > [60015.902572] kernel:  ? check_preempt_curr+0x2f/0x70
> > [60015.902576] kernel:  ? selinux_file_ioctl+0x137/0x1e0
> > [60015.902579] kernel:  ? expand_files+0x1cb/0x1d0
> > [60015.902582] kernel:  ? __x64_sys_ioctl+0x82/0xb0
> > [60015.902585] kernel:  __x64_sys_ioctl+0x82/0xb0
> > [60015.902588] kernel:  do_syscall_64+0x33/0x40
> > [60015.902591] kernel:  entry_SYSCALL_64_after_hwframe+0x44/0xae
> > [60015.902595] kernel: RIP: 0033:0x7f158e38f0ab
>
> The problem is we end up trying to start a transaction while in a send
> context, which is unexpected. But it does happen if memory allocation
> triggers inode eviction due to memory pressure.
>
> You don't have CONFIG_BTRFS_ASSERT=y in your kernel config right?

No, but Fedora debug kernels do have it enabled so I can ask the
reporter to use 5.12.10-debug or 5.13-rc6. Any preference?


> That would trigger an assertion right away:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/fs/btrfs/transaction.c?h=v5.12.10#n584
>
> With assertions disabled, we just cast current->journal_info into a
> transaction handle and dereference it, which is obviously wrong since
> ->jornal_info has a value that is not a pointer to a transaction
> handle, resulting in the crash.
>
> How easy is it to reproduce for you?

I'm not sure.

Do you think following this splat we could have somehow been IO
limited or stalled without any other kernel messages appearing? That
would then cause reclaim activity, and high memory and swap usage? I'm
wondering if it's likely or unlikely, because at the moment I think
it's unlikely since /var/log/journal was successfully recording
systemd-journald journals for the 81 minutes between this call trace
and when systemd-oomd started killing things. I'm trying to separate
out what's causing what.

> Can you try the following patch and see if everything works as expected?

I'll ask the reporter. I don't have a setup even remotely approximate
to this one for testing.

Thanks!

-- 
Chris Murphy