Subject: Re: [BUG] [powerpc] [next-20260216/17] nfsd: use-after-free in cache_check_rcu() triggered by sosreport on ppc64le

From: Jeff Layton <[email-masked]>
Date: Fri, 01 May 2026 08:06:22 +0100

On Fri, 2026-05-01 at 02:15 +0530, Misbah Anjum N wrote:
> Hi,
> 
> Following up on my bug report, I have completed a git bisect and have 
> critical new findings to report.
> Ref: 
> https://lore.kernel.org/linux-next/[email-masked]/T/#u
> 
> Current Status: Bug Has Propagated from linux-next to Mainline.
> First Bad commit identified: da6b5aae84beb0917ecb0c9fbc71169d145397ff
> 
> The use-after-free bug in cache_check_rcu() that I originally reported 
> in linux-next (6.19.0-next-20260216/17) has now propagated into mainline 
> and is confirmed present in:
> - mainline (Tested on Latest kernel as of 2026-04-30 - commit 
> 08d0d3466664)
> - linux-next (Tested on Latest kernel as of 2026-04-30)
> 
> This bug is causing failures on ppc64le systems:
> 1. Kernel panics: 100% reproducible crashes when sosreport runs
> 2. CI/Testing failures: All automated Avocado-vt KVM testing on ppc64le 
> is failing
> 3. Use-after-free corruption: Memory corruption with corrupted pointers 
> containing
>     ASCII strings ("libz.so.", "export_cap") or poison patterns 
> (0xcccccccccccccccc)
> 

Thanks for the bug report. I must have missed your earlier email.

The commit you landed on is a merge commit and is not likely to be the
cause, particularly since that merge was for x86 drivers and you're
seeing this on PPC. Is this reproducible on other architectures?

What might be best is to run this test with KASAN enabled. That might
give us a clearer picture of what object is being freed and when.

> Test Environment:
> Architecture: ppc64le (IBM Power11 and IBM Power10)
> Hypervisor: phyp (PowerVM)
> Distribution: Fedora 42 (Server Edition Prerelease)
> Reproducible: 100%
> 
> Reproduction Steps:
> On ppc64le system with latest kernel:
> 1. Run: modprobe nfsd
> 2. Run: sosreport
> System crashes (typically within 30-60 seconds)
> 
> First bad commit:
> commit da6b5aae84beb0917ecb0c9fbc71169d145397ff
> Merge: b69e478512080 344bf523d441d
> Author: Linus Torvalds <[email-masked]>
> Date:   Mon Apr 20 10:15:32 2026 -0700
>      Merge tag 'platform-drivers-x86-v7.1-1' of
>      
> git://git.kernel.org/pub/scm/linux/kernel/git/pdx86/platform-drivers-x86
>      Pull x86 platform driver updates from Ilpo Järvinen:
>       "asus-wmi:
>         - Retain battery charge threshold during boot which avoids
>           unsolicited change to 100%. Return -ENODATA when the limit
>           is not yet known
>         - Improve screenpad power/brightness handling consistency
>         - Fix screenpad brightness range
>        barco-p50-gpio:
>         - Normalize gpio_get return values
>        bitland-mifs-wmi:
>         - Add driver for Bitland laptops (supports platform profile,
>           hwmon, kbd backlight, gpu mode, hotkeys, and fan boost)
>        dell_rbu:
>         - Fix using uninitialized value in sysfs write function
>        dell-wmi-sysman:
>         - Respect destination length when constructing enum strings
>        hp-wmi:
>         - Propagate fan setting apply failures and log an error
>         - Fix sysfs write vs work handler cancel_delayed_work_sync() 
> deadlock
>         - Correct keepalive schedule_delayed_work() to mod_delayed_work()
>         - Fix u8 underflows in GPU delta calculation
>         - Use mutex to protect fan pwm/mode
>         - Ignore kbd backlight and FnLock key events that are handled by 
> FW
>         - Fix fan table parsing (use correct field)
>         - Add support for Omen 14-fb0xxx, 16-n0xxx, 16-wf1xxx, and
>           Omen MAX 16-ak0xxxx
>        input: trackpoint & thinkpad_acpi:
>         - Enable doubletap by default and add sysfs enable/disable
>        int3472:
>         - Add support for GPIO type 0x02 (IR flood LED)
>        intel-speed-select: (updated to v1.26)
>         - Avoid using current base frequency as maximum
>         - Fix CPU extended family ID decoding
>         - Fix exit code
>         - Improve error reporting
>        intel/vsec:
>         - Refactor to support ACPI-enumerated PMT endpoints.
>        pcengines-apuv2:
>         - Attach software node to the gpiochip
>        uniwill:
>         - Refactor hwmon to smaller parts to accomodate HW diversity
>         - Support USB-C power/performance priority switch through sysfs
>         - Add another XMG Fusion 15 (L19) DMI vendor
>         - Enable fine-grained features to device lineup mapping
>        wmi:
>         - Perform output size check within WMI core to allow simpler WMI
>           drivers
>        misc:
>         - acpi_driver -> platform driver conversions (a large number of
>           changes from Rafael J. Wysocki)
>         - cleanups / refactoring / improvements"
>      * tag 'platform-drivers-x86-v7.1-1' of 
> git://git.kernel.org/pub/scm/linux/kernel/git/pdx86/platform-drivers-x86: 
> (106 commits)
>        platform/x86: hp-wmi: Add support for Omen 16-wf1xxx (8C77)
>        platform/x86: hp-wmi: Add support for Omen 16-n0xxx (8A44)
>        platform/x86: hp-wmi: Add support for OMEN MAX 16-ak0xxx (8D87)
>        platform/x86: hp-wmi: fix fan table parsing
>        platform/x86: hp-wmi: add Omen 14-fb0xxx (board 8C58) support
>        platform/wmi: Replace .no_notify_data with .min_event_size
>        platform/wmi: Extend wmidev_query_block() to reject undersized 
> data
>        platform/wmi: Extend wmidev_invoke_method() to reject undersized 
> data
>        platform/wmi: Prepare to reject undersized unmarshalling results
>        platform/wmi: Convert drivers to use wmidev_invoke_procedure()
>        platform/wmi: Add wmidev_invoke_procedure()
>        platform/x86: int3472: Add support for GPIO type 0x02 (IR flood 
> LED)
>        platform/x86: int3472: Parameterize LED con_id in registration
>        platform/x86: int3472: Rename pled to led in LED registration code
>        platform/x86: int3472: Use local variable for LED struct access
>        platform/x86: thinkpad_acpi: remove obsolete TODO comment
>        platform/x86: dell-wmi-sysman: bound enumeration string 
> aggregation
>        platform/x86: hp-wmi: Ignore backlight and FnLock events
>        platform/x86: uniwill-laptop: Fix signedness bug
>        platform/x86: dell_rbu: avoid uninit value usage in 
> packet_size_write()
>        ...
>   .../sysfs-driver-uniwill-laptop       |  27 +
>   .../laptops/thinkpad-acpi.rst         |  21 +
>   .../laptops/uniwill-laptop.rst        |  12 +
>   .../wmi/devices/bitland-mifs-wmi.rst  | 207 +++
>   .../wmi/driver-development-guide.rst  |  11 +-
>   drivers/gpu/drm/xe/xe_debugfs.c       |   2 +-
>   drivers/gpu/drm/xe/xe_hwmon.c         |   2 +-
>   drivers/gpu/drm/xe/xe_vsec.c          |   7 +-
>   drivers/gpu/drm/xe/xe_vsec.h          |   4 +-
>   drivers/input/mouse/trackpoint.c      |  46 +
>   drivers/input/mouse/trackpoint.h      |   5 +
>   .../platform/mellanox/nvsw-sn2201.c   |   1 -
>   .../surface/surface_hotplug.c         |   2 +-
>   .../surface/surfacepro3_button.c      |  71 +-
>   drivers/platform/wmi/core.c           |  89 +-
>   drivers/platform/wmi/internal.h       |   3 +-
>   drivers/platform/wmi/marshalling.c    |   6 +-
>   .../wmi/tests/marshalling_kunit.c     |  24 +-
>   drivers/platform/x86/Kconfig          |  18 +
>   drivers/platform/x86/Makefile         |   1 +
>   drivers/platform/x86/acer-wireless.c  |  48 +-
>   drivers/platform/x86/asus-laptop.c    |  44 +-
>   drivers/platform/x86/asus-wireless.c  |  55 +-
>   drivers/platform/x86/asus-wmi.c       |  77 +-
>   drivers/platform/x86/barco-p50-gpio.c |  23 +-
>   .../platform/x86/bitland-mifs-wmi.c   | 837 +++++++++++++
>   drivers/platform/x86/dell/dell-rbtn.c | 142 ++-
>   .../platform/x86/dell/dell-wmi-base.c |   1 +
>   .../dell-wmi-sysman/dell-wmi-sysman.h |   4 +-
>   .../dell-wmi-sysman/enum-attributes.c |  34 +-
>   .../x86/dell/dell-wmi-sysman/sysman.c |  68 +-
>   drivers/platform/x86/dell/dell_rbu.c  |   6 +-
>   drivers/platform/x86/eeepc-laptop.c   |  45 +-
>   drivers/platform/x86/fujitsu-laptop.c | 489 ++++----
>   drivers/platform/x86/fujitsu-tablet.c |  30 +-
>   drivers/platform/x86/hp/hp-wmi.c      | 125 +-
>   .../x86/intel/int3472/discrete.c      |  13 +-
>   .../platform/x86/intel/int3472/led.c  |  55 +-
>   drivers/platform/x86/intel/pmc/core.c |   4 +-
>   .../x86/intel/pmc/ssram_telemetry.c   |   2 +-
>   .../platform/x86/intel/pmt/class.c    |   8 +-
>   .../platform/x86/intel/pmt/class.h    |   5 +-
>   .../x86/intel/pmt/discovery.c         |   4 +-
>   .../x86/intel/pmt/telemetry.c         |  13 +-
>   .../x86/intel/pmt/telemetry.h         |  12 +-
>   drivers/platform/x86/intel/rst.c      |  23 +-
>   drivers/platform/x86/intel/sdsi.c     |   5 +-
>   .../platform/x86/intel/smartconnect.c |  23 +-
>   drivers/platform/x86/intel/vsec.c     | 121 +-
>   .../platform/x86/intel/vsec_tpmi.c    |  12 +-
>   .../x86/intel/wmi/sbl-fw-update.c     |   7 +-
>   .../x86/intel/wmi/thunderbolt.c       |   2 +-
>   .../x86/lenovo/ideapad-laptop.c       |   1 +
>   .../x86/lenovo/thinkpad_acpi.c        | 193 ++-
>   .../platform/x86/lenovo/wmi-camera.c  |   1 +
>   .../platform/x86/lenovo/wmi-events.c  |   1 +
>   drivers/platform/x86/lenovo/ymc.c     |   1 +
>   .../platform/x86/lenovo/yogabook.c    |   2 +-
>   drivers/platform/x86/lg-laptop.c      |  51 +-
>   drivers/platform/x86/mxm-wmi.c        |  12 -
>   .../platform/x86/panasonic-laptop.c   |  79 +-
>   .../platform/x86/pcengines-apuv2.c    |   3 +-
>   drivers/platform/x86/redmi-wmi.c      |   1 +
>   drivers/platform/x86/sony-laptop.c    | 122 +-
>   drivers/platform/x86/system76_acpi.c  |  63 +-
>   drivers/platform/x86/topstar-laptop.c |  43 +-
>   drivers/platform/x86/toshiba_acpi.c   | 182 +--
>   .../platform/x86/toshiba_bluetooth.c  |  74 +-
>   drivers/platform/x86/toshiba_haps.c   |  57 +-
>   .../x86/uniwill/uniwill-acpi.c        | 440 +++++--
>   .../x86/uniwill/uniwill-wmi.c         |   1 +
>   .../platform/x86/wireless-hotkey.c    |  49 +-
>   drivers/platform/x86/wmi-bmof.c       |   2 +-
>   drivers/platform/x86/xiaomi-wmi.c     |   1 +
>   include/linux/intel_vsec.h            |  39 +-
>   .../linux/platform_data/x86/int3472.h |  12 +-
>   include/linux/wmi.h                   |  15 +-
>   .../intel-speed-select/isst-config.c  |  41 +-
>   78 files changed, 3073 insertions(+), 1309 deletions(-)
>   create mode 100644 Documentation/wmi/devices/bitland-mifs-wmi.rst
>   create mode 100644 drivers/platform/x86/bitland-mifs-wmi.c
> 
> Complete Bisect Log:
> git bisect start
> # good: [eb0d6d97c27c29cd7392c8fd74f46edf7dff7ec2] Merge tag 'bpf-fixes'
> git bisect good eb0d6d97c27c29cd7392c8fd74f46edf7dff7ec2
> # bad: [d46dd0d88341e45f8e0226fdef5462f5270898fc] Merge tag 
> 'f2fs-for-7.1-rc1'
> git bisect bad d46dd0d88341e45f8e0226fdef5462f5270898fc
> # good: [99ef60d119f3b2621067dd5fc1ea4a37360709e4] Merge tag 
> 'usb-7.1-rc1'
> git bisect good 99ef60d119f3b2621067dd5fc1ea4a37360709e4
> # good: [b69e478512080f9bb03ed3e812b759bb73e2837b] Merge tag 
> 'backlight-next-7.1'
> git bisect good b69e478512080f9bb03ed3e812b759bb73e2837b
> # bad: [a85d6ff99411eb21536a750ad02205e8a97894c6] Merge tag 'scsi-misc'
> git bisect bad a85d6ff99411eb21536a750ad02205e8a97894c6
> # bad: [ce9e93383ad71da468dafb9944a539808bf91c06] Merge tag 
> 'sh-for-v7.1-tag1'
> git bisect bad ce9e93383ad71da468dafb9944a539808bf91c06
> # good: [378500dc1313e2c06a2f675bb00ab5d7880433ba] platform/x86: 
> asus-laptop: Register ACPI notify handler directly
> git bisect good 378500dc1313e2c06a2f675bb00ab5d7880433ba
> # good: [9d317a54e46d3b6420567dc5b63e9d7ff5c064a3] platform/x86: hp-wmi: 
> fix fan table parsing
> git bisect good 9d317a54e46d3b6420567dc5b63e9d7ff5c064a3
> # bad: [b66cb4f156fe47f52065e70eb1b2f12ccd0c2884] Merge tag 
> 'printk-for-7.1'
> git bisect bad b66cb4f156fe47f52065e70eb1b2f12ccd0c2884
> # good: [add9d911be9b141706ccf41d17b4043ed1bc12a1] Merge branch 
> 'rework/prb-fixes' into for-linus
> git bisect good add9d911be9b141706ccf41d17b4043ed1bc12a1
> # bad: [da6b5aae84beb0917ecb0c9fbc71169d145397ff] Merge tag 
> 'platform-drivers-x86-v7.1-1'
> git bisect bad da6b5aae84beb0917ecb0c9fbc71169d145397ff
> # good: [899225257e78585e2e10b0f7ba472b3c212a8d16] platform/x86: hp-wmi: 
> Add support for Omen 16-n0xxx (8A44)
> git bisect good 899225257e78585e2e10b0f7ba472b3c212a8d16
> # good: [344bf523d441d44c75c429ea6cdcfa8f12efde4d] platform/x86: hp-wmi: 
> Add support for Omen 16-wf1xxx (8C77)
> git bisect good 344bf523d441d44c75c429ea6cdcfa8f12efde4d
> # first bad commit: [da6b5aae84beb0917ecb0c9fbc71169d145397ff] Merge tag 
> 'platform-drivers-x86-v7.1-1'
> 
> Crash Log Call Trace:
> [ 1721.304746] BUG: Unable to handle kernel data access on read at 
> 0x50000004e
> [ 1721.304751] Faulting instruction address: 0xc008000015b11d9c
> [ 1721.304756] Oops: Kernel access of bad area, sig: 11 [#1]
> [ 1721.304760] LE PAGE_SIZE=64K MMU=Radix  SMP NR_CPUS=2048 NUMA pSeries
> [ 1721.304767] Modules linked in: nft_masq nft_ct nft_reject_ipv4 
> nf_reject_ipv4 nft_reject act_csum cls_u32 sch_htb nft_chain_nat nf_nat 
> nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nf_tables bridge stp llc 
> binfmt_misc rpcrdma rdma_cm iw_cm ib_cm kvm_hv ib_core kvm bonding 
> rfkill pseries_rng vmx_crypto nfsd auth_rpcgss nfs_acl drm lockd grace 
> loop drm_panel_orientation_quirks nfnetlink vsock_loopback 
> vmw_vsock_virtio_transport_common vsock zram xfs dm_service_time sd_mod 
> ibmvscsi ibmveth scsi_transport_srp ipr btrfs xor libblake2b raid6_pq 
> zstd_compress sunrpc dm_mirror dm_region_hash dm_log be2iscsi bnx2i cnic 
> uio cxgb4i cxgb4 tls libcxgbi libcxgb qla4xxx iscsi_boot_sysfs iscsi_tcp 
> libiscsi_tcp libiscsi scsi_transport_iscsi dm_multipath fuse dm_mod
> [ 1721.304844] CPU: 32 UID: 0 PID: 7187 Comm: sosreport Not tainted 
> 7.0.0-12182-gda6b5aae84be #17 PREEMPTLAZY
> [ 1721.304849] Hardware name: IBM,9080-HEX POWER10 (architected) 
> 0x800200 0xf000006 of:IBM,FW1060.70 (NH1060_166) hv:phyp pSeries
> [ 1721.304854] NIP:  c008000015b11d9c LR: c008000015b121a0 CTR: 
> c008000015b12138
> [ 1721.304858] REGS: c0000010bfef7750 TRAP: 0300   Not tainted  
> (7.0.0-12182-gda6b5aae84be)
> [ 1721.304862] MSR:  8000000000009033 <SF,EE,ME,IR,DR,RI,LE>  CR: 
> 28044402  XER: 00000000
> [ 1721.304871] CFAR: c008000015b1219c DAR: 000000050000004e DSISR: 
> 40000000 IRQMASK: 0
> [ 1721.304871] GPR00: c008000015b121a0 c0000010bfef79f0 c008000014737a00 
> c00000002091f400
> [ 1721.304871] GPR04: 0000000500000026 0000000000000000 0000000000000000 
> c0000000a66ce800
> [ 1721.304871] GPR08: c00000002091f400 0000000000000000 0000000000400cc0 
> 0000000000000000
> [ 1721.304871] GPR12: c008000015b12138 c000001bfffff300 0000000000000000 
> 0000000000000000
> [ 1721.304871] GPR16: 0000000000000000 0000000000000000 0000000000000000 
> 0000000000000000
> [ 1721.304871] GPR20: 0000000000000000 0000000000000000 c00000101bb29f08 
> c00000101bb29ef8
> [ 1721.304871] GPR24: 000000007fff0000 0000000000000000 fffffffffffff000 
> 0000000000000000
> [ 1721.304871] GPR28: c00000002091f400 0000000000000000 c00000101bb29ed0 
> 0000000500000026
> [ 1721.304911] NIP [c008000015b11d9c] cache_check_rcu+0x44/0x2c0 
> [sunrpc]
> [ 1721.304950] LR [c008000015b121a0] c_show+0x68/0x1c0 [sunrpc]
> [ 1721.304984] Call Trace:
> [ 1721.304986] [c0000010bfef79f0] [c0000010bfef7a30] 0xc0000010bfef7a30 
> (unreliable)
> [ 1721.304992] [c0000010bfef7aa0] [c008000015b121a0] c_show+0x68/0x1c0 
> [sunrpc]
> [ 1721.305027] [c0000010bfef7b50] [c0000000007b9b28] 
> seq_read_iter+0x1a8/0x680
> [ 1721.305034] [c0000010bfef7c20] [c0000000007ba104] 
> seq_read+0x104/0x150
> [ 1721.305038] [c0000010bfef7cc0] [c000000000863920] 
> proc_reg_read+0xf0/0x160
> [ 1721.305043] [c0000010bfef7cf0] [c000000000768b00] vfs_read+0xe0/0x3d0
> [ 1721.305049] [c0000010bfef7db0] [c000000000769a08] 
> ksys_read+0x78/0x140
> [ 1721.305054] [c0000010bfef7e00] [c000000000034908] 
> system_call_exception+0x128/0x360
> [ 1721.305061] [c0000010bfef7e50] [c00000000000d6a0] 
> system_call_common+0x160/0x2e4
> [ 1721.305066] ---- interrupt: c00 at 0x7fffba6b9fc8
> [ 1721.305069] NIP:  00007fffba6b9fc8 LR: 00007fffba6a8438 CTR: 
> 0000000000000000
> [ 1721.305072] REGS: c0000010bfef7e80 TRAP: 0c00   Not tainted  
> (7.0.0-12182-gda6b5aae84be)
> [ 1721.305075] MSR:  800000000280f033 
> <SF,VEC,VSX,EE,PR,FP,ME,IR,DR,RI,LE>  CR: 28044404  XER: 00000000
> [ 1721.305085] IRQMASK: 0
> [ 1721.305085] GPR00: 0000000000000003 00007fffa77ed9b0 00007fffba847c00 
> 0000000000000007
> [ 1721.305085] GPR04: 00007fff940230f0 0000000000010000 0000000000000000 
> 0000000000000000
> [ 1721.305085] GPR08: 0000000000000000 0000000000000000 0000000000000000 
> 0000000000000000
> [ 1721.305085] GPR12: 0000000000000000 00007fffa77f6880 0000000000000000 
> 0000000000000000
> [ 1721.305085] GPR16: 0000000000000000 0000000000000000 00007fffb87f0828 
> 00007fffa77edf68
> [ 1721.305085] GPR20: 00007fffb87f0830 00007fffbaded480 00007fffb87f0838 
> 00007fffbae0d480
> [ 1721.305085] GPR24: 00007fffbaf8e0f0 00007fff940230f0 0000000000000007 
> 00007fffac001290
> [ 1721.305085] GPR28: 0000000000000000 00007fffa77ef8b0 00007fffa4590b40 
> 0000000000010000
> [ 1721.305120] NIP [00007fffba6b9fc8] 0x7fffba6b9fc8
> [ 1721.305122] LR [00007fffba6a8438] 0x7fffba6a8438
> [ 1721.305125] ---- interrupt: c00
> [ 1721.305127] Code: fba1ffe8 fbe1fff8 fb61ffd8 fbc1fff0 7c9f2378 
> 7c7c1b78 7cbd2b78 f8010010 f821ff51 e92d0c78 f9210078 39200000 
> <e9240028> 71290001 418201cc fb410080
> [ 1721.305141] ---[ end trace 0000000000000000 ]---
> [ 1721.307464] pstore: backend (nvram) writing error (-1)
> [ 1721.307468]
> [ 1722.307472] Kernel panic - not syncing: Fatal exception
> [ 1722.321570] Rebooting in 10 seconds..
> 
> Thanks,
> Misbah Anjum N <[email-masked]>
> 
> 
> On 2026-02-19 18:57, Misbah Anjum N wrote:
> > Hi,
> > 
> > I'm reporting a critical use-after-free bug in linux-next NFS server
> > code that causes kernel crashes when sosreport reads /proc/fs/nfsd/*
> > files. This appears to be a recent regression affecting ppc64le
> > systems.
> > The bug is 100% reproducible and shows corrupted pointers containing
> > ASCII strings (library names, export cache names) instead of valid
> > kernel addresses, indicating freed memory has been reallocated.
> > 
> > Thanks,
> > Misbah Anjum N
> > 
> > Bug Description:
> > The kernel crashes with use-after-free in cache_check_rcu() [sunrpc]
> > when sosreport reads NFS export information from /proc. The bug is
> > highly reproducible and consistently shows corrupted pointers
> > containing ASCII strings (library names, export cache names,
> > filesystem paths) instead of valid kernel addresses.
> > This is a critical regression in linux-next that needs to be fixed
> > before reaching mainline.
> > 
> > System Information:
> > Kernel: 6.19.0-next-20260216 and 6.19.0-next-20260217
> > Architecture: ppc64le (IBM Power11, 9080-HEX)
> > Hardware: IBM,9080-HEX Power11 (architected) 0x820200 0xf000007
> > Firmware: IBM,FW1110.11 (NH1110_102)
> > Hypervisor: phyp (PowerVM)
> > Distribution: Fedora 42 (Server Edition Prerelease)
> > Reproducible: 100%
> > 
> > Reproduction Steps:
> > On ppc64le system with kernel 6.19.0-next-20260216/17:
> > 1. Run: modprobe nfsd
> > 2. Run: sosreport
> > System crashes (typically within 30-60 seconds)
> > 
> > Important notes:
> > 1. Direct cat /proc/fs/nfsd/exports does NOT trigger the crash
> > 2. The crash is triggered by sosreport's specific access pattern to
> > /proc/fs/nfsd/* files
> > 3. No NFS exports or active NFS server configuration needed
> > 4. Reproducible 100% of the time with sosreport
> > 
> > Kernel Configuration:
> > Relevant NFS configuration options:
> > CONFIG_NFSD=m
> > CONFIG_NFSD_V3_ACL=y
> > CONFIG_NFSD_V4=y
> > CONFIG_NFSD_PNFS=y
> > CONFIG_NFSD_SCSILAYOUT=y
> > CONFIG_NFSD_V4_2_INTER_SSC=y
> > CONFIG_NFSD_V4_SECURITY_LABEL=y
> > CONFIG_NFS_FS=m
> > CONFIG_NFS_V3=m
> > CONFIG_NFS_V3_ACL=y
> > CONFIG_NFS_V4=m
> > CONFIG_NFS_V4_1=y
> > CONFIG_NFS_V4_2=y
> > CONFIG_NFS_V4_SECURITY_LABEL=y
> > CONFIG_NFS_FSCACHE=y
> > CONFIG_NFS_DEBUG=y
> > CONFIG_NFS_DISABLE_UDP_SUPPORT=y
> > CONFIG_NFS_ACL_SUPPORT=m
> > CONFIG_NFS_COMMON=y
> > CONFIG_SUNRPC=m
> > CONFIG_SUNRPC_DEBUG=y
> > 
> > Detailed Crash Traces:
> > Crash #1 - cache_check_rcu() with "export_cap" pointer 
> > (6.19.0-next-20260216)
> > [ 3162.071511] BUG: Unable to handle kernel data access at 
> > 0x657079745f70618b
> > [ 3162.071529] Faulting instruction address: 0xc0080000083322bc
> > [ 3162.071534] Oops: Kernel access of bad area, sig: 11 [#1]
> > [ 3162.071537] LE PAGE_SIZE=64K MMU=Radix  SMP NR_CPUS=2048 NUMA 
> > pSeries
> > [ 3162.071542] Modules linked in: binfmt_misc vhost_net vhost
> > vhost_iotlb tap tun nft_masq nft_ct nft_reject_ipv4 nf_reject_ipv4
> > nft_reject act_csum cls_u32 sch_htb nft_chain_nat nf_nat nf_conntrack
> > nf_defrag_ipv6 nf_defrag_ipv4 nf_tables bridge stp llc rpcrdma rdma_cm
> > iw_cm kvm_hv ib_cm ib_core kvm bonding rfkill nfsd auth_rpcgss nfs_acl
> > lockd grace pseries_rng vmx_crypto drm loop
> > drm_panel_orientation_quirks nfnetlink vsock_loopback
> > vmw_vsock_virtio_transport_common vsock zram xfs dm_service_time
> > sd_mod ibmvscsi ibmveth scsi_transport_srp tg3 ipr btrfs xor
> > libblake2b raid6_pq zstd_compress sunrpc dm_mirror dm_region_hash
> > dm_log be2iscsi bnx2i cnic uio cxgb4i cxgb4 tls libcxgbi libcxgb
> > qla4xxx iscsi_boot_sysfs iscsi_tcp libiscsi_tcp libiscsi
> > scsi_transport_iscsi dm_multipath fuse dm_mod
> > [ 3162.071618] CPU: 51 UID: 0 PID: 52936 Comm: sosreport Kdump: loaded
> > Not tainted 6.19.0-next-20260216 #1 PREEMPTLAZY
> > [ 3162.071623] Hardware name: IBM,9080-HEX Power11 (architected)
> > 0x820200 0xf000007 of:IBM,FW1110.11 (NH1110_102) hv:phyp pSeries
> > [ 3162.071627] NIP:  c0080000083322bc LR: c0080000115f6b48 CTR: 
> > c008000008332278
> > [ 3162.071631] REGS: c0000000b353f7c0 TRAP: 0380   Not tainted
> > (6.19.0-next-20260216)
> > [ 3162.071635] MSR:  8000000000009033 <SF,EE,ME,IR,DR,RI,LE>  CR:
> > 48044402  XER: 00000000
> > [ 3162.071643] CFAR: c00800001164e15c IRQMASK: 0
> > [ 3162.071643] GPR00: c0080000115f6b48 c0000000b353fa60
> > c008000008397600 c00000012a758700
> > [ 3162.071643] GPR04: 657079745f706163 0000000000000000
> > 0000000000000000 c000000144b4d000
> > [ 3162.071643] GPR08: c00000012a758700 0000000000000000
> > 0000000000400cc0 c00800001164e148
> > [ 3162.071643] GPR12: c008000008332278 c0000027fde49f00
> > 0000000000000000 0000000000000000
> > [ 3162.071643] GPR16: 0000000000000000 0000000000000000
> > 0000000000000000 0000000000000000
> > [ 3162.071643] GPR20: 0000000000000000 0000000000000000
> > c000000145433788 c000000145433778
> > [ 3162.071643] GPR24: 000000007fff0000 0000000000000000
> > fffffffffffff000 0000000000000000
> > [ 3162.071643] GPR28: c00000012a758700 0000000000000000
> > c00000012a758700 657079745f706163
> > [ 3162.071682] NIP [c0080000083322bc] cache_check_rcu+0x44/0x2c0 
> > [sunrpc]
> > [ 3162.071716] LR [c0080000115f6b48] e_show+0x40/0x260 [nfsd]
> > [ 3162.071747] Call Trace:
> > [ 3162.071749] [c0000000b353fa60] [c0000000b353fb50]
> > 0xc0000000b353fb50 (unreliable)
> > [ 3162.071754] [c0000000b353fb10] [c0080000115f6b48] e_show+0x40/0x260 
> > [nfsd]
> > [ 3162.071780] [c0000000b353fb50] [c0000000007a7468] 
> > seq_read_iter+0x1a8/0x680
> > [ 3162.071787] [c0000000b353fc20] [c0000000007a7a44] 
> > seq_read+0x104/0x150
> > [ 3162.071791] [c0000000b353fcc0] [c00000000084ecb0] 
> > proc_reg_read+0xf0/0x160
> > [ 3162.071796] [c0000000b353fcf0] [c000000000756b00] 
> > vfs_read+0xe0/0x3d0
> > [ 3162.071800] [c0000000b353fdb0] [c000000000757a08] 
> > ksys_read+0x78/0x140
> > [ 3162.071804] [c0000000b353fe00] [c0000000000348c8]
> > system_call_exception+0x128/0x350
> > [ 3162.071809] [c0000000b353fe50] [c00000000000d6a0]
> > system_call_common+0x160/0x2e4
> > [ 3162.071815] ---- interrupt: c00 at 0x7fff7ecb9fc8
> > [ 3162.071818] NIP:  00007fff7ecb9fc8 LR: 00007fff7eca8438 CTR: 
> > 0000000000000000
> > [ 3162.071821] REGS: c0000000b353fe80 TRAP: 0c00   Not tainted
> > (6.19.0-next-20260216)
> > [ 3162.071824] MSR:  800000000280f033
> > <SF,VEC,VSX,EE,PR,FP,ME,IR,DR,RI,LE>  CR: 28044404  XER: 00000000
> > [ 3162.071834] IRQMASK: 0
> > [ 3162.071834] GPR00: 0000000000000003 00007fff6afdd9d0
> > 00007fff7ee47c00 0000000000000005
> > [ 3162.071834] GPR04: 00007fff5c0223c0 0000000000010000
> > 0000000000000000 0000000000000000
> > [ 3162.071834] GPR08: 0000000000000000 0000000000000000
> > 0000000000000000 0000000000000000
> > [ 3162.071834] GPR12: 0000000000000000 00007fff6afe68a0
> > 0000000000000000 0000000000000000
> > [ 3162.071834] GPR16: 0000000000000000 0000000000000000
> > 00007fff7d800828 00007fff6afddf88
> > [ 3162.071834] GPR20: 00007fff7d800830 00007fff7f3ed480
> > 00007fff7d800838 00007fff7f40d480
> > [ 3162.071834] GPR24: 00007fff7f58e0f0 00007fff5c0223c0
> > 0000000000000005 00007fff6c001290
> > [ 3162.071834] GPR28: 0000000000000000 00007fff6afdf8d0
> > 00007fff79db3140 0000000000010000
> > [ 3162.071870] NIP [00007fff7ecb9fc8] 0x7fff7ecb9fc8
> > [ 3162.071872] LR [00007fff7eca8438] 0x7fff7eca8438
> > [ 3162.071875] ---- interrupt: c00
> > [ 3162.071877] Code: fba1ffe8 fbe1fff8 fb61ffd8 fbc1fff0 7c9f2378
> > 7c7c1b78 7cbd2b78 f8010010 f821ff51 e92d0c78 f9210078 39200000
> > <e9240028> 71290001 418201cc fb410080
> > [ 3162.071890] ---[ end trace 0000000000000000 ]---
> > 
> > Crash #2 - d_path() NULL pointer dereference (6.19.0-next-20260217)
> > [ 5489.374563] Kernel attempted to read user page (60) - exploit
> > attempt? (uid: 0)
> > [ 5489.374582] BUG: Kernel NULL pointer dereference on read at 
> > 0x00000060
> > [ 5489.374586] Faulting instruction address: 0xc0000000007cb354
> > [ 5489.374590] Oops: Kernel access of bad area, sig: 11 [#1]
> > [ 5489.374593] LE PAGE_SIZE=64K MMU=Radix  SMP NR_CPUS=2048 NUMA 
> > pSeries
> > [ 5489.374598] Modules linked in: binfmt_misc vhost_net vhost
> > vhost_iotlb tap tun nft_masq nft_ct nft_reject_ipv4 nf_reject_ipv4
> > nft_reject act_csum cls_u32 sch_htb nft_chain_nat nf_nat nf_conntrack
> > nf_defrag_ipv6 nf_defrag_ipv4 nf_tables bridge stp llc rpcrdma rdma_cm
> > iw_cm kvm_hv ib_cm kvm ib_core bonding rfkill nfsd auth_rpcgss nfs_acl
> > lockd grace pseries_rng vmx_crypto drm loop
> > drm_panel_orientation_quirks nfnetlink vsock_loopback
> > vmw_vsock_virtio_transport_common vsock zram xfs dm_service_time
> > sd_mod ibmvscsi tg3 ibmveth scsi_transport_srp ipr btrfs xor
> > libblake2b raid6_pq zstd_compress sunrpc dm_mirror dm_region_hash
> > dm_log be2iscsi bnx2i cnic uio cxgb4i cxgb4 tls libcxgbi libcxgb
> > qla4xxx iscsi_boot_sysfs iscsi_tcp libiscsi_tcp libiscsi
> > scsi_transport_iscsi dm_multipath fuse dm_mod
> > [ 5489.374671] CPU: 2 UID: 0 PID: 45718 Comm: sosreport Kdump: loaded
> > Not tainted 6.19.0-next-20260217 #1 PREEMPTLAZY
> > [ 5489.374676] Hardware name: IBM,9080-HEX Power11 (architected)
> > 0x820200 0xf000007 of:IBM,FW1110.11 (NH1110_102) hv:phyp pSeries
> > [ 5489.374680] NIP:  c0000000007cb354 LR: c0000000007a7ed0 CTR: 
> > c0000000007a7e60
> > [ 5489.374683] REGS: c00000026f2676b0 TRAP: 0300   Not tainted
> > (6.19.0-next-20260217)
> > [ 5489.374688] MSR:  8000000000009033 <SF,EE,ME,IR,DR,RI,LE>  CR:
> > 88044408  XER: 00000000
> > [ 5489.374696] CFAR: c0000000007a7ecc DAR: 0000000000000060 DSISR:
> > 40000000 IRQMASK: 0
> > [ 5489.374696] GPR00: c0000000007a7ed0 c00000026f267950
> > c000000001868100 0000000000000000
> > [ 5489.374696] GPR04: c0000012e1350002 000000000000fffe
> > c00800000ee360f0 c0000012e1350002
> > [ 5489.374696] GPR08: 000000000000fffe c000000146400840
> > c0000012e1360000 0000000000000000
> > [ 5489.374696] GPR12: c0000000007a7e60 c0000027ffffdf00
> > 0000000000000000 0000000000000000
> > [ 5489.374696] GPR16: 0000000000000000 0000000000000000
> > 0000000000000000 0000000000000000
> > [ 5489.374696] GPR20: 0000000000000000 0000000000000000
> > c0000000bbca06c8 c0000000bbca06b8
> > [ 5489.374696] GPR24: 000000007fff0000 0000000000000000
> > fffffffffffff000 0000000000000000
> > [ 5489.374696] GPR28: c00000026f267c50 c000000140db5800
> > c000000146400800 c0000012e1350002
> > [ 5489.374736] NIP [c0000000007cb354] d_path+0x44/0x210
> > [ 5489.374742] LR [c0000000007a7ed0] seq_path+0x70/0x160
> > [ 5489.374747] Call Trace:
> > [ 5489.374749] [c00000026f267950] [0000000000000006] 0x6 (unreliable)
> > [ 5489.374755] [c00000026f2679b0] [c0000000007a7ed0] 
> > seq_path+0x70/0x160
> > [ 5489.374759] [c00000026f2679f0] [c00800001144673c]
> > svc_export_show+0x1d4/0x5a0 [nfsd]
> > [ 5489.374789] [c00000026f267aa0] [c008000004a126fc] c_show+0xa4/0x1c0 
> > [sunrpc]
> > [ 5489.374819] [c00000026f267b50] [c0000000007a7468] 
> > seq_read_iter+0x1a8/0x680
> > [ 5489.374824] [c00000026f267c20] [c0000000007a7a44] 
> > seq_read+0x104/0x150
> > [ 5489.374829] [c00000026f267cc0] [c00000000084ecb0] 
> > proc_reg_read+0xf0/0x160
> > [ 5489.374833] [c00000026f267cf0] [c000000000756af0] 
> > vfs_read+0xe0/0x3d0
> > [ 5489.374837] [c00000026f267db0] [c0000000007579f8] 
> > ksys_read+0x78/0x140
> > [ 5489.374841] [c00000026f267e00] [c0000000000348c8]
> > system_call_exception+0x128/0x350
> > [ 5489.374846] [c00000026f267e50] [c00000000000d6a0]
> > system_call_common+0x160/0x2e4
> > [ 5489.374852] ---- interrupt: c00 at 0x7fff866b9fc8
> > [ 5489.374855] NIP:  00007fff866b9fc8 LR: 00007fff866a8438 CTR: 
> > 0000000000000000
> > [ 5489.374858] REGS: c00000026f267e80 TRAP: 0c00   Not tainted
> > (6.19.0-next-20260217)
> > [ 5489.374861] MSR:  800000000280f033
> > <SF,VEC,VSX,EE,PR,FP,ME,IR,DR,RI,LE>  CR: 28044404  XER: 00000000
> > [ 5489.374871] IRQMASK: 0
> > [ 5489.374871] GPR00: 0000000000000003 00007fff71fbd9d0
> > 00007fff86847c00 0000000000000008
> > [ 5489.374871] GPR04: 00007fff600228e0 0000000000010000
> > 0000000000000000 0000000000000000
> > [ 5489.374871] GPR08: 0000000000000000 0000000000000000
> > 0000000000000000 0000000000000000
> > [ 5489.374871] GPR12: 0000000000000000 00007fff71fc68a0
> > 0000000000000000 0000000000000000
> > [ 5489.374871] GPR16: 0000000000000000 0000000000000000
> > 00007fff847f0828 00007fff71fbdf88
> > [ 5489.374871] GPR20: 00007fff847f0830 00007fff86ded480
> > 00007fff847f0838 00007fff86e0d480
> > [ 5489.374871] GPR24: 00007fff86f8e0f0 00007fff600228e0
> > 0000000000000008 00007fff6c0016a0
> > [ 5489.374871] GPR28: 0000000000000000 00007fff71fbf8d0
> > 00007fff80548c40 0000000000010000
> > [ 5489.374906] NIP [00007fff866b9fc8] 0x7fff866b9fc8
> > [ 5489.374909] LR [00007fff866a8438] 0x7fff866a8438
> > [ 5489.374912] ---- interrupt: c00
> > [ 5489.374914] Code: f8010010 f821ffa1 f8410018 e92d0c78 f9210058
> > 39200000 91410044 7c691b78 7d442a14 f9410038 e8630008 90a10040
> > <e9430060> 2c2a0000 41820064 e98a0048
> > [ 5489.374927] ---[ end trace 0000000000000000 ]---
> > 
> > Crash #3 - cache_check_rcu() with "libz.so." pointer 
> > (6.19.0-next-20260217)
> > [   63.748591] BUG: Unable to handle kernel data access at 
> > 0x2e6f732e7a626994
> > [   63.748601] Faulting instruction address: 0xc008000009de22bc
> > [   63.748606] Oops: Kernel access of bad area, sig: 11 [#1]
> > [   63.748609] LE PAGE_SIZE=64K MMU=Radix  SMP NR_CPUS=2048 NUMA 
> > pSeries
> > [   63.748614] Modules linked in: nft_masq nft_ct nft_reject_ipv4
> > nf_reject_ipv4 nft_reject act_csum cls_u32 sch_htb nft_chain_nat
> > nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nf_tables bridge stp
> > llc binfmt_misc rpcrdma rdma_cm iw_cm kvm_hv ib_cm kvm ib_core bonding
> > rfkill nfsd auth_rpcgss nfs_acl lockd grace pseries_rng vmx_crypto drm
> > loop drm_panel_orientation_quirks nfnetlink vsock_loopback
> > vmw_vsock_virtio_transport_common vsock zram xfs dm_service_time
> > sd_mod tg3 ibmvscsi ibmveth scsi_transport_srp ipr btrfs xor
> > libblake2b raid6_pq zstd_compress sunrpc dm_mirror dm_region_hash
> > dm_log be2iscsi bnx2i cnic uio cxgb4i cxgb4 tls libcxgbi libcxgb
> > qla4xxx iscsi_boot_sysfs iscsi_tcp libiscsi_tcp libiscsi
> > scsi_transport_iscsi dm_multipath fuse dm_mod
> > [   63.748680] CPU: 58 UID: 0 PID: 5675 Comm: sosreport Kdump: loaded
> > Not tainted 6.19.0-next-20260217 #1 PREEMPTLAZY
> > [   63.748686] Hardware name: IBM,9080-HEX Power11 (architected)
> > 0x820200 0xf000007 of:IBM,FW1110.11 (NH1110_102) hv:phyp pSeries
> > [   63.748690] NIP:  c008000009de22bc LR: c00800000f086b48 CTR: 
> > c008000009de2278
> > [   63.748693] REGS: c0000000a3a4f7c0 TRAP: 0380   Not tainted
> > (6.19.0-next-20260217)
> > [   63.748697] MSR:  8000000000009033 <SF,EE,ME,IR,DR,RI,LE>  CR:
> > 48044402  XER: 00000000
> > [   63.748706] CFAR: c00800000f0de15c IRQMASK: 0
> > [   63.748706] GPR00: c00800000f086b48 c0000000a3a4fa60
> > c008000006f47600 c0000000b70f9b00
> > [   63.748706] GPR04: 2e6f732e7a62696c 0000000000000000
> > 0000000000000000 c000000152f70800
> > [   63.748706] GPR08: c0000000b70f9b00 0000000000000000
> > 0000000000400cc0 c00800000f0de148
> > [   63.748706] GPR12: c008000009de2278 c0000027fde40700
> > 0000000000000000 0000000000000000
> > [   63.748706] GPR16: 0000000000000000 0000000000000000
> > 0000000000000000 0000000000000000
> > [   63.748706] GPR20: 0000000000000000 0000000000000000
> > c0000000e2e17b08 c0000000e2e17af8
> > [   63.748706] GPR24: 000000007fff0000 0000000000000000
> > fffffffffffff000 0000000000000000
> > [   63.748706] GPR28: c0000000b70f9b00 0000000000000000
> > c0000000b70f9b00 2e6f732e7a62696c
> > [   63.748744] NIP [c008000009de22bc] cache_check_rcu+0x44/0x2c0 
> > [sunrpc]
> > [   63.748776] LR [c00800000f086b48] e_show+0x40/0x260 [nfsd]
> > [   63.748805] Call Trace:
> > [   63.748807] [c0000000a3a4fa60] [c0000000a3a4fb50]
> > 0xc0000000a3a4fb50 (unreliable)
> > [   63.748812] [c0000000a3a4fb10] [c00800000f086b48] e_show+0x40/0x260 
> > [nfsd]
> > [   63.748839] [c0000000a3a4fb50] [c0000000007a7468] 
> > seq_read_iter+0x1a8/0x680
> > [   63.748845] [c0000000a3a4fc20] [c0000000007a7a44] 
> > seq_read+0x104/0x150
> > [   63.748850] [c0000000a3a4fcc0] [c00000000084ecb0] 
> > proc_reg_read+0xf0/0x160
> > [   63.748855] [c0000000a3a4fcf0] [c000000000756af0] 
> > vfs_read+0xe0/0x3d0
> > [   63.748859] [c0000000a3a4fdb0] [c0000000007579f8] 
> > ksys_read+0x78/0x140
> > [   63.748862] [c0000000a3a4fe00] [c0000000000348c8]
> > system_call_exception+0x128/0x350
> > [   63.748868] [c0000000a3a4fe50] [c00000000000d6a0]
> > system_call_common+0x160/0x2e4
> > [   63.748873] ---- interrupt: c00 at 0x7fffa74b9fc8
> > [   63.748876] NIP:  00007fffa74b9fc8 LR: 00007fffa74a8438 CTR: 
> > 0000000000000000
> > [   63.748879] REGS: c0000000a3a4fe80 TRAP: 0c00   Not tainted
> > (6.19.0-next-20260217)
> > [   63.748882] MSR:  800000000280f033
> > <SF,VEC,VSX,EE,PR,FP,ME,IR,DR,RI,LE>  CR: 28044404  XER: 00000000
> > [   63.748892] IRQMASK: 0
> > [   63.748892] GPR00: 0000000000000003 00007fff8b7ed9d0
> > 00007fffa7647c00 0000000000000008
> > [   63.748892] GPR04: 00007fff7c021af0 0000000000010000
> > 0000000000000000 0000000000000000
> > [   63.748892] GPR08: 0000000000000000 0000000000000000
> > 0000000000000000 0000000000000000
> > [   63.748892] GPR12: 0000000000000000 00007fff8b7f68a0
> > 0000000000000000 0000000000000000
> > [   63.748892] GPR16: 0000000000000000 0000000000000000
> > 00007fffa55f0828 00007fff8b7edf88
> > [   63.748892] GPR20: 00007fffa55f0830 00007fffa7bed480
> > 00007fffa55f0838 00007fffa7c0d480
> > [   63.748892] GPR24: 00007fffa7d8e0f0 00007fff7c021af0
> > 0000000000000008 00007fff94001290
> > [   63.748892] GPR28: 0000000000000000 00007fff8b7ef8d0
> > 00007fffa062be00 0000000000010000
> > [   63.748927] NIP [00007fffa74b9fc8] 0x7fffa74b9fc8
> > [   63.748930] LR [00007fffa74a8438] 0x7fffa74a8438
> > [   63.748933] ---- interrupt: c00
> > [   63.748935] Code: fba1ffe8 fbe1fff8 fb61ffd8 fbc1fff0 7c9f2378
> > 7c7c1b78 7cbd2b78 f8010010 f821ff51 e92d0c78 f9210078 39200000
> > <e9240028> 71290001 418201cc fb410080
> > [   63.748948] ---[ end trace 0000000000000000 ]---
> > 
> > Next Steps:
> > I have vmcore dumps from multiple crashes and am working on:
> > 1. Crash utility analysis to examine the corrupted cache structures
> > 2. Git bisect to identify the problematic commit

-- 
Jeff Layton <[email-masked]>