Message-ID: <aYpp_ShERlNvt4T_@aschofie-mobl2.lan>
Date: Mon, 9 Feb 2026 15:13:01 -0800
From: Alison Schofield <alison.schofield@...el.com>
To: John Groves <john@...alactic.com>
CC: John Groves <John@...ves.net>, Miklos Szeredi <miklos@...redi.hu>, "Dan
 Williams" <dan.j.williams@...el.com>, Bernd Schubert <bschubert@....com>,
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Subject: Re: [PATCH V4 0/2] ndctl: Add daxctl support for the new "famfs"
 mode of devdax

On Sun, Jan 18, 2026 at 10:36:02PM +0000, John Groves wrote:
> From: John Groves <john@...ves.net>
> 
> No change since V2 - re-sending due to technical challenges.
> 
> No change since V1 - reposting as V2 to keep this with the related
> kernel (dax and fuse) patches and libfuse patches.
> 
> This short series adds support and tests to daxctl for famfs[1]. The
> famfs kernel patch series, under the same "compound cover" as this
> series, adds a new 'fsdev_dax' driver for devdax. When that driver
> is bound (instead of device_dax), the device is in 'famfs' mode rather
> than 'devdax' mode.
> 

Hi John, 

I fired this all up and ran it. It got through all but it's last test
case before failing.

Three things appended:
1) the diff I applied to daxctl-famfs.sh to run the test
2) testlog.txt output of the test
3) RIP: 0010:is_free_buddy_page+0x39/0x60 kernel log


1) Diff I applied to execute the test:

diff --git a/test/daxctl-famfs.sh b/test/daxctl-famfs.sh
index 12fbfefa3144..a4e8d87b9762 100755
--- a/test/daxctl-famfs.sh
+++ b/test/daxctl-famfs.sh
@@ -9,6 +9,17 @@ rc=77
 
 trap 'cleanup $LINENO' ERR
 
+# Use cxl-test module to get the DAX device of the CXL auto region,
+# which also makes this test NON destructive.
+#
+# The $CXL list below is a delay because find_daxdev() was not
+# finding the DAX region without it.
+#
+modprobe -r cxl-test
+modprobe cxl-test
+$CXL list
+
+
 daxdev=""
 original_mode=""

2) Log of Meson test suite run on 2026-02-09T14:52:40.498801

1/1 ndctl:dax / daxctl-famfs.sh INTERRUPT      230.60s   killed by signal 15 SIGTERM
22:52:40 MALLOC_PERTURB_=233 LC_ALL=C TEST_PATH=/root/ndctl/build/test NDCTL=/root/ndctl/build/ndctl/ndctl DAXCTL=/root/ndctl/build/daxctl/daxctl DATA_PATH=/root/ndctl/test CXL=/root/ndctl/build/cxl/cxl /root/ndctl/test/daxctl-famfs.sh
----------------------------------- output -----------------------------------
stdout:

Found dax device: dax6.0 (current mode: system-ram)

=== Testing famfs mode transitions ===
Device is in system-ram mode, attempting to convert to devdax...
[
  {
    "chardev":"dax6.0",
    "size":536870912,
    "target_node":0,
    "align":2097152,
    "mode":"devdax"
  }
]
Initial mode: devdax - OK
Testing devdax -> famfs... [
  {
    "chardev":"dax6.0",
    "size":536870912,
    "target_node":0,
    "align":2097152,
    "mode":"famfs"
  }
]
OK
Testing famfs -> famfs (re-enable)... [
  {
    "chardev":"dax6.0",
    "size":536870912,
    "target_node":0,
    "align":2097152,
    "mode":"famfs"
  }
]
OK
Testing famfs -> devdax... [
  {
    "chardev":"dax6.0",
    "size":536870912,
    "target_node":0,
    "align":2097152,
    "mode":"devdax"
  }
]
OK
Testing devdax -> devdax (re-enable)... [
  {
    "chardev":"dax6.0",
    "size":536870912,
    "target_node":0,
    "align":2097152,
    "mode":"devdax"
  }
]
OK

=== Testing JSON output for mode field ===
Testing JSON output for devdax mode... OK
[
  {
    "chardev":"dax6.0",
    "size":536870912,
    "target_node":0,
    "align":2097152,
    "mode":"famfs"
  }
]
Testing JSON output for famfs mode... OK
[
  {
    "chardev":"dax6.0",
    "size":536870912,
    "target_node":0,
    "align":2097152,
    "mode":"devdax"
  }
]

=== Testing error handling ===
[
  {
    "chardev":"dax6.0",
    "size":536870912,
    "target_node":0,
    "align":2097152,
    "mode":"famfs"
  }
]
Testing invalid mode rejection... OK (correctly rejected)
[
  {
    "chardev":"dax6.0",
    "size":536870912,
    "target_node":0,
    "align":2097152,
    "mode":"devdax"
  }
]

=== Testing system-ram transitions with famfs ===
Testing devdax -> system-ram... [
  {
    "chardev":"dax6.0",
    "size":536870912,
    "target_node":0,
    "align":2097152,
    "mode":"system-ram",
    "online_memblocks":0,
    "total_memblocks":4
  }
]
OK
Testing system-ram -> famfs (should fail)... OK (correctly rejected)
Testing system-ram -> devdax -> famfs... [
  {
    "chardev":"dax6.0",
    "size":536870912,
    "target_node":0,
    "align":2097152,
    "mode":"devdax"
  }
]
[
  {
    "chardev":"dax6.0",
    "size":536870912,
    "target_node":0,
    "align":2097152,
    "mode":"famfs"
  }
]
OK
[
  {
    "chardev":"dax6.0",
    "size":536870912,
    "target_node":0,
    "align":2097152,
    "mode":"devdax"
  }
]

Restoring device to original mode: system-ram
Error at line 255
stderr:
+ rc=77
++ dirname /root/ndctl/test/daxctl-famfs.sh
+ . /root/ndctl/test/common
+++ basename /root/ndctl/test/daxctl-famfs.sh
++ test_basename=daxctl-famfs.sh
++ '[' -z /root/ndctl/build/ndctl/ndctl ']'
++ '[' -z /root/ndctl/build/daxctl/daxctl ']'
++ '[' -z /root/ndctl/build/cxl/cxl ']'
++ '[' -z /root/ndctl/build/test ']'
++ NFIT_TEST_BUS0=nfit_test.0
++ NFIT_TEST_BUS1=nfit_test.1
++ CXL_TEST_BUS=cxl_test
++ ACPI_BUS=ACPI.NFIT
++ E820_BUS=e820
++ CXL_TEST_QOS_CLASS=42
+ trap 'cleanup $LINENO' ERR
+ modprobe -r cxl-test
+ modprobe cxl-test
+ /root/ndctl/build/cxl/cxl list
+ daxdev=
+ original_mode=
+ main
+ check_fsdev_dax
+ modinfo fsdev_dax
+ return 0
+ find_daxdev
++ /root/ndctl/build/daxctl/daxctl list
++ jq -er '.[0].chardev // empty'
+ daxdev=dax6.0
+ [[ ! -n dax6.0 ]]
++ /root/ndctl/build/daxctl/daxctl list -d dax6.0
++ jq -er '.[].mode'
+ original_mode=system-ram
+ printf 'Found dax device: %s (current mode: %s)\n' dax6.0 system-ram
+ rc=1
+ test_famfs_mode_transitions
+ printf '\n=== Testing famfs mode transitions ===\n'
+ ensure_devdax_mode
+ local mode
++ daxctl_get_mode dax6.0
++ /root/ndctl/build/daxctl/daxctl list -d dax6.0
++ jq -er '.[].mode'
+ mode=system-ram
+ [[ system-ram == \d\e\v\d\a\x ]]
+ [[ system-ram == \s\y\s\t\e\m\-\r\a\m ]]
+ printf 'Device is in system-ram mode, attempting to convert to devdax...\n'
+ /root/ndctl/build/daxctl/daxctl reconfigure-device -f -m devdax dax6.0
dax6.0: all memory sections (4) already offline
reconfigured 1 device
++ daxctl_get_mode dax6.0
++ /root/ndctl/build/daxctl/daxctl list -d dax6.0
++ jq -er '.[].mode'
+ [[ devdax == \d\e\v\d\a\x ]]
++ daxctl_get_mode dax6.0
++ /root/ndctl/build/daxctl/daxctl list -d dax6.0
++ jq -er '.[].mode'
+ [[ devdax == \d\e\v\d\a\x ]]
+ printf 'Initial mode: devdax - OK\n'
+ printf 'Testing devdax -> famfs... '
+ /root/ndctl/build/daxctl/daxctl reconfigure-device -m famfs dax6.0
reconfigured 1 device
++ daxctl_get_mode dax6.0
++ /root/ndctl/build/daxctl/daxctl list -d dax6.0
++ jq -er '.[].mode'
+ [[ famfs == \f\a\m\f\s ]]
+ printf 'OK\n'
+ printf 'Testing famfs -> famfs (re-enable)... '
+ /root/ndctl/build/daxctl/daxctl reconfigure-device -m famfs dax6.0
reconfigured 1 device
++ daxctl_get_mode dax6.0
++ /root/ndctl/build/daxctl/daxctl list -d dax6.0
++ jq -er '.[].mode'
+ [[ famfs == \f\a\m\f\s ]]
+ printf 'OK\n'
+ printf 'Testing famfs -> devdax... '
+ /root/ndctl/build/daxctl/daxctl reconfigure-device -m devdax dax6.0
reconfigured 1 device
++ daxctl_get_mode dax6.0
++ /root/ndctl/build/daxctl/daxctl list -d dax6.0
++ jq -er '.[].mode'
+ [[ devdax == \d\e\v\d\a\x ]]
+ printf 'OK\n'
+ printf 'Testing devdax -> devdax (re-enable)... '
+ /root/ndctl/build/daxctl/daxctl reconfigure-device -m devdax dax6.0
reconfigured 1 device
++ daxctl_get_mode dax6.0
++ /root/ndctl/build/daxctl/daxctl list -d dax6.0
++ jq -er '.[].mode'
+ [[ devdax == \d\e\v\d\a\x ]]
+ printf 'OK\n'
+ test_json_output
+ printf '\n=== Testing JSON output for mode field ===\n'
+ ensure_devdax_mode
+ local mode
++ daxctl_get_mode dax6.0
++ /root/ndctl/build/daxctl/daxctl list -d dax6.0
++ jq -er '.[].mode'
+ mode=devdax
+ [[ devdax == \d\e\v\d\a\x ]]
+ return 0
+ printf 'Testing JSON output for devdax mode... '
++ /root/ndctl/build/daxctl/daxctl list -d dax6.0
++ jq -er '.[].mode'
+ mode=devdax
+ [[ devdax == \d\e\v\d\a\x ]]
+ printf 'OK\n'
+ /root/ndctl/build/daxctl/daxctl reconfigure-device -m famfs dax6.0
reconfigured 1 device
+ printf 'Testing JSON output for famfs mode... '
++ /root/ndctl/build/daxctl/daxctl list -d dax6.0
++ jq -er '.[].mode'
+ mode=famfs
+ [[ famfs == \f\a\m\f\s ]]
+ printf 'OK\n'
+ /root/ndctl/build/daxctl/daxctl reconfigure-device -m devdax dax6.0
reconfigured 1 device
+ test_error_handling
+ printf '\n=== Testing error handling ===\n'
+ /root/ndctl/build/daxctl/daxctl reconfigure-device -m famfs dax6.0
reconfigured 1 device
+ printf 'Testing invalid mode rejection... '
+ /root/ndctl/build/daxctl/daxctl reconfigure-device -m invalidmode dax6.0
+ printf 'OK (correctly rejected)\n'
+ /root/ndctl/build/daxctl/daxctl reconfigure-device -m devdax dax6.0
reconfigured 1 device
+ check_kmem
+ modinfo kmem
+ return 0
++ cat /sys/devices/system/memory/auto_online_blocks
+ saved_policy=offline
+ echo offline
+ test_system_ram_transitions
+ printf '\n=== Testing system-ram transitions with famfs ===\n'
+ ensure_devdax_mode
+ local mode
++ daxctl_get_mode dax6.0
++ /root/ndctl/build/daxctl/daxctl list -d dax6.0
++ jq -er '.[].mode'
+ mode=devdax
+ [[ devdax == \d\e\v\d\a\x ]]
+ return 0
++ daxctl_get_mode dax6.0
++ /root/ndctl/build/daxctl/daxctl list -d dax6.0
++ jq -er '.[].mode'
+ [[ devdax == \d\e\v\d\a\x ]]
+ printf 'Testing devdax -> system-ram... '
+ /root/ndctl/build/daxctl/daxctl reconfigure-device -N -m system-ram dax6.0
reconfigured 1 device
++ daxctl_get_mode dax6.0
++ /root/ndctl/build/daxctl/daxctl list -d dax6.0
++ jq -er '.[].mode'
+ [[ system-ram == \s\y\s\t\e\m\-\r\a\m ]]
+ printf 'OK\n'
+ printf 'Testing system-ram -> famfs (should fail)... '
+ /root/ndctl/build/daxctl/daxctl reconfigure-device -m famfs dax6.0
+ printf 'OK (correctly rejected)\n'
+ printf 'Testing system-ram -> devdax -> famfs... '
+ /root/ndctl/build/daxctl/daxctl reconfigure-device -f -m devdax dax6.0
dax6.0: all memory sections (4) already offline
reconfigured 1 device
++ daxctl_get_mode dax6.0
++ /root/ndctl/build/daxctl/daxctl list -d dax6.0
++ jq -er '.[].mode'
+ [[ devdax == \d\e\v\d\a\x ]]
+ /root/ndctl/build/daxctl/daxctl reconfigure-device -m famfs dax6.0
reconfigured 1 device
++ daxctl_get_mode dax6.0
++ /root/ndctl/build/daxctl/daxctl list -d dax6.0
++ jq -er '.[].mode'
+ [[ famfs == \f\a\m\f\s ]]
+ printf 'OK\n'
+ /root/ndctl/build/daxctl/daxctl reconfigure-device -m devdax dax6.0
reconfigured 1 device
+ echo offline
+ printf '\nRestoring device to original mode: %s\n' system-ram
+ /root/ndctl/build/daxctl/daxctl reconfigure-device -f -m system-ram dax6.0
/root/ndctl/test/daxctl-famfs.sh: line 231:  1266 Killed                  "$DAXCTL" reconfigure-device -f -m "$original_mode" "$daxdev"
++ cleanup 255
++ printf 'Error at line %d\n' 255
++ [[ -n dax6.0 ]]
++ [[ -n system-ram ]]
++ /root/ndctl/build/daxctl/daxctl reconfigure-device -f -m system-ram dax6.0
------------------------------------------------------------------------------

Summary of Failures:

1/1 ndctl:dax / daxctl-famfs.sh INTERRUPT      230.60s   killed by signal 15 SIGTERM

Ok:                 0   
Expected Fail:      0   
Fail:               1   
Unexpected Pass:    0   
Skipped:            0   
Timeout:            0   

3) BUG: unable to handle page fault for address: ffffc9000f508033
[  343.806681] #PF: supervisor read access in kernel mode
[  343.808158] #PF: error_code(0x0000) - not-present page
[  343.809635] PGD 80a067 P4D 80a067 PUD 1936067 PMD 12eeb9067 PTE 0
[  343.811357] Oops: Oops: 0000 [#1] SMP NOPTI
[  343.812634] CPU: 4 UID: 0 PID: 1266 Comm: daxctl Tainted: G           O        6.19.0-rc5+ #106 PREEMPT(voluntary) 
[  343.815263] Tainted: [O]=OOT_MODULE
[  343.816423] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
[  343.818507] RIP: 0010:is_free_buddy_page+0x39/0x60
[  343.819466] Code: 00 00 00 48 c1 fe 06 eb 0a 48 83 c1 01 48 83 f9 0b 74 30 44 89 c0 48 89 fa d3 e0 83 e8 01 48 98 48 21 f0 48 c1 e0 06 48 29 c2 <80> 7a 33 f0 75 d9 48 8b 42 28 48 39 c8 72 d0 b8 01 00 00 00 c3 cc
[  343.822668] RSP: 0018:ffffc9000f50f828 EFLAGS: 00010286
[  343.823719] RAX: 0000000000007a80 RBX: ffffc9000f50f8a0 RCX: 0000000000000009
[  343.825021] RDX: ffffc9000f508000 RSI: ffffff7c003d43ea RDI: ffffc9000f50fa80
[  343.826343] RBP: ffffc9000f50f838 R08: 0000000000000001 R09: 00000000ffefffff
[  343.827651] R10: ffffc9000f50fa38 R11: ffff888376ffe000 R12: ffffc9000f50fa80
[  343.828834] R13: ffffc9000f50f9a0 R14: 0000000000000006 R15: 0000000000000001
[  343.829725] FS:  00007f0f83e087c0(0000) GS:ffff8881fa8f8000(0000) knlGS:0000000000000000
[  343.830765] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  343.831581] CR2: ffffc9000f508033 CR3: 000000012dec6003 CR4: 0000000000370ef0
[  343.832517] Call Trace:
[  343.832964]  <TASK>
[  343.833385]  ? set_ps_flags.constprop.0+0x3c/0x70
[  343.834099]  snapshot_page+0x2ca/0x330
[  343.834679]  __dump_page+0x2e/0x380
[  343.835260]  ? up+0x5a/0x90
[  343.835757]  dump_page+0x16/0x50
[  343.836324]  ? dump_page+0x16/0x50
[  343.836861]  __get_pfnblock_flags_mask+0x6f/0xd0
[  343.837520]  get_pfnblock_migratetype+0xe/0x30
[  343.838192]  __dump_page+0x15b/0x380
[  343.838692]  dump_page+0x16/0x50
[  343.839111]  ? dump_page+0x16/0x50
[  343.839504]  __set_pfnblock_flags_mask.constprop.0+0x6f/0xf0
[  343.840093]  init_pageblock_migratetype+0x39/0x60
[  343.840589]  memmap_init_range+0x165/0x290
[  343.841069]  move_pfn_range_to_zone+0xed/0x200
[  343.841548]  mhp_init_memmap_on_memory+0x23/0xb0
[  343.842062]  memory_subsys_online+0x127/0x1a0
[  343.842542]  device_online+0x4d/0x90
[  343.842986]  state_store+0x96/0xa0
[  343.843393]  dev_attr_store+0x12/0x30
[  343.843809]  sysfs_kf_write+0x48/0x70
[  343.844231]  kernfs_fop_write_iter+0x160/0x210
[  343.844714]  vfs_write+0x261/0x500
[  343.845185]  ksys_write+0x5c/0xf0
[  343.845584]  __x64_sys_write+0x14/0x20
[  343.846040]  x64_sys_call+0x1fbc/0x1ff0
[  343.846480]  do_syscall_64+0x67/0x370
[  343.846905]  entry_SYSCALL_64_after_hwframe+0x71/0x79
[  343.847432] RIP: 0033:0x7f0f83d01c37
[  343.847838] Code: 0f 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 48 89 54 24 18 48 89 74 24
[  343.849536] RSP: 002b:00007ffe63e1f148 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[  343.850282] RAX: ffffffffffffffda RBX: 00007ffe63e1f708 RCX: 00007f0f83d01c37
[  343.850997] RDX: 000000000000000f RSI: 00007f0f83ef543e RDI: 0000000000000004
[  343.851692] RBP: 00007ffe63e1f180 R08: 0000000000000000 R09: 0000000000000073
[  343.852405] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
[  343.853112] R13: 00007ffe63e1f740 R14: 0000000000414da0 R15: 00007f0f83f3b000
[  343.853789]  </TASK>
[  343.854109] Modules linked in: cxl_test(O) cxl_mem(O) cxl_pmem(O) cxl_acpi(O) cxl_port(O) cxl_mock(O) device_dax(O) fsdev_dax kmem dax_cxl cxl_mock_mem(O) cxl_core(O) dax_pmem(O) nd_pmem(O) nd_btt(O) nfit(O) nd_e820(O) libnvdimm(O) nfit_test_iomap(O) [last unloaded: cxl_mock(O)]
[  343.856252] CR2: ffffc9000f508033
[  343.856656] ---[ end trace 0000000000000000 ]---
[  343.857172] RIP: 0010:is_free_buddy_page+0x39/0x60
[  343.857678] Code: 00 00 00 48 c1 fe 06 eb 0a 48 83 c1 01 48 83 f9 0b 74 30 44 89 c0 48 89 fa d3 e0 83 e8 01 48 98 48 21 f0 48 c1 e0 06 48 29 c2 <80> 7a 33 f0 75 d9 48 8b 42 28 48 39 c8 72 d0 b8 01 00 00 00 c3 cc
[  343.859395] RSP: 0018:ffffc9000f50f828 EFLAGS: 00010286
[  343.859929] RAX: 0000000000007a80 RBX: ffffc9000f50f8a0 RCX: 0000000000000009
[  343.860614] RDX: ffffc9000f508000 RSI: ffffff7c003d43ea RDI: ffffc9000f50fa80
[  343.861333] RBP: ffffc9000f50f838 R08: 0000000000000001 R09: 00000000ffefffff
[  343.862076] R10: ffffc9000f50fa38 R11: ffff888376ffe000 R12: ffffc9000f50fa80
[  343.862753] R13: ffffc9000f50f9a0 R14: 0000000000000006 R15: 0000000000000001
[  343.863477] FS:  00007f0f83e087c0(0000) GS:ffff8881fa8f8000(0000) knlGS:0000000000000000
[  343.864268] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  343.864855] CR2: ffffc9000f508033 CR3: 000000012dec6003 CR4: 0000000000370ef0
[  343.865542] note: daxctl[1266] exited with irqs disabled

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