Re: [PATCH v4 19/21] uio: replace deprecated mmap hook with mmap_prepare in uio_info

[Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>]

On Mar 20, 2026 / 22:39, Lorenzo Stoakes (Oracle) wrote:
> The f_op->mmap interface is deprecated, so update uio_info to use its
> successor, mmap_prepare.
> 
> Therefore, replace the uio_info->mmap hook with a new
> uio_info->mmap_prepare hook, and update its one user, target_core_user,
> to both specify this new mmap_prepare hook and also to use the new
> vm_ops->mapped() hook to continue to maintain a correct udev->kref
> refcount.
> 
> Then update uio_mmap() to utilise the mmap_prepare compatibility layer to
> invoke this callback from the uio mmap invocation.
> 
> Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>

Hello Lorenzo, since two weeks ago, I observe a failure during my kernel test
set targeting Linux for-next branch. On failure, kernel reported a WARN at
__vma_check_mmap_hook [1]. I bisected and found that this patch is the trigger.
Here I share my observations of the failure. Actions or advices for fix will be
appreciated.


The failure happens when TCMU device is set up with targetcli. When tcmu-runner
is running, the command lines below should successfully create a backstore for a
TCMU device, but it fails.

  $ sudo targetcli
  targetcli shell version 3.0.1
  Copyright 2011-2013 by Datera, Inc and others.
  For help on commands, type 'help'.
  
  /> cd /backstores/user:zbc
  /backstores/user:zbc> create name=test size=1M cfgstring=@/tmp/tmp.img
  UserBackedStorageObject creation failed.

On failure, tcmu-runner reports mmap failures:

  2026-04-13 12:23:49.271 1103 [CRIT] main:1302: Starting...
  2026-04-13 12:23:49.461 1103 [INFO] load_our_module:575: Inserted module 'target_core_user'
  2026-04-13 12:23:49.480 1103 [INFO] tcmur_register_handler:92: Handler fbo is registered
  2026-04-13 12:23:49.486 1103 [INFO] tcmur_register_handler:92: Handler zbc is registered
  2026-04-13 12:23:51.202 1103 [INFO] tcmur_register_handler:92: Handler rbd is registered
  2026-04-13 12:27:24.522 1103 [ERROR] device_open_shm:523: could not mmap /dev/uio0
  2026-04-13 12:27:24.550 1103 [ERROR] device_open_shm:523: could not mmap /dev/uio0

The failure was found with user:zbc handler. I confirmed that the failure is
recreated with fbo handler also. Then, this failure looks common for all TCMU
users.

At the failrue, kernel reported the WARN at __vma_check_mmap_hook [1]. The line
1287 in mm/util.c reported the WARN:

  1284 int __vma_check_mmap_hook(struct vm_area_struct *vma)
  1285 {
  1286         /* vm_ops->mapped is not valid if mmap() is specified. */
  1287         if (vma->vm_ops && WARN_ON_ONCE(vma->vm_ops->mapped))
  1288                 return -EINVAL;
  1289
  1290         return 0;
  1291 }
  1292 EXPORT_SYMBOL(__vma_check_mmap_hook);

When I reverted the commit from the kernel tag next-20260409, the failrue
disappeared.

If other information is required for fix, please let me know. Thanks in advance.


[1] dmesg

WARNING: mm/util.c:1287 at __vma_check_mmap_hook+0x61/0x90, CPU#0: tcmu-runner/1332
Modules linked in: target_core_pscsi target_core_file target_core_iblock xfs target_core_user target_core_mod rfkill nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject 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 nf_tables ip6table_filter ip6_tables iptable_filter ip_tables qrtr irdma intel_rapl_msr intel_rapl_common ice intel_uncore_frequency intel_uncore_frequency_common skx_edac skx_edac_common libie_fwlog nfit sunrpc gnss idpf libnvdimm x86_pkg_temp_thermal libeth_xdp intel_powerclamp libeth ib_core spi_nor mtd coretemp kvm_intel kvm i40e iTCO_wdt irqbypass intel_pmc_bxt rapl ses vfat intel_cstate libie fat intel_uncore libie_adminq enclosure i2c_i801 spi_intel_pci i2c_smbus spi_intel lpc_ich wmi joydev mei_me ioatdma acpi_power_meter acpi_pad mei intel_pch_thermal dca fuse loop dm_multipath nfnetlink zram
 lz4hc_compress lz4_compress zstd_compress ast drm_client_lib i2c_algo_bit drm_shmem_helper drm_kms_helper nvme drm mpi3mr nvme_core scsi_transport_sas nvme_keyring nvme_auth scsi_dh_rdac scsi_dh_emc scsi_dh_alua pkcs8_key_parser i2c_dev [last unloaded: null_blk]
CPU: 0 UID: 0 PID: 1332 Comm: tcmu-runner Not tainted 7.0.0-rc6-next-20260401-kts #1 PREEMPT(lazy) 
Hardware name: Supermicro Super Server/X11SPi-TF, BIOS 3.5 05/18/2021
RIP: 0010:__vma_check_mmap_hook+0x61/0x90
Code: 00 00 00 00 fc ff df 48 8d 78 10 48 89 f9 48 c1 e9 03 80 3c 11 00 75 2a 48 83 78 10 00 75 0b 31 c0 48 83 c4 08 c3 cc cc cc cc <0f> 0b b8 ea ff ff ff eb ee 48 89 04 24 e8 6d 4c 1f 00 48 8b 04 24
RSP: 0018:ffff8881391f7488 EFLAGS: 00010282
RAX: ffffffffc2abca40 RBX: 0000000000000000 RCX: 1ffffffff855794a
RDX: dffffc0000000000 RSI: 0000000000000000 RDI: ffffffffc2abca50
RBP: ffff8881391f76a0 R08: ffffffffa10016e9 R09: ffffed102723ee44
R10: ffffed102723ee45 R11: 0000000000000000 R12: ffff8881391f78e0
R13: ffff8881391f78f0 R14: ffff88810d1ec780 R15: ffff8881391f7a78
FS:  00007f154f1a9840(0000) GS:ffff888e9b440000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f5efd40fe88 CR3: 000000010cfbf005 CR4: 00000000007726f0
PKRU: 55555554
Call Trace:
 <TASK>
 __mmap_new_vma+0x116e/0x18d0
 ? __pfx___mmap_new_vma+0x10/0x10
 ? vma_merge_new_range+0x495/0xa00
 ? __pfx_vma_merge_new_range+0x10/0x10
 ? lock_acquire+0x126/0x140
 __mmap_region+0x651/0xa00
 ? __pfx_process_measurement+0x10/0x10
 ? __pfx___mmap_region+0x10/0x10
 ? __lock_acquire+0x55d/0xbd0
 ? __lock_acquire+0x55d/0xbd0
 ? lock_is_held_type+0x9a/0x110
 ? mas_find+0xc9/0x690
 ? arch_get_unmapped_area_topdown+0x2a7/0x890
 mmap_region+0x3c2/0x4c0
 ? __pfx_mmap_region+0x10/0x10
 ? security_mmap_addr+0x54/0xd0
 ? __get_unmapped_area+0x18c/0x300
 ? __pfx_uio_mmap+0x10/0x10
 do_mmap+0xa26/0x10f0
 ? lock_acquire+0x126/0x140
 ? __pfx_do_mmap+0x10/0x10
 ? __pfx_down_write_killable+0x10/0x10
 ? __lock_acquire+0x55d/0xbd0
 vm_mmap_pgoff+0x218/0x3a0
 ? __pfx_vm_mmap_pgoff+0x10/0x10
 ? __fget_files+0x1b4/0x2f0
 ksys_mmap_pgoff+0x229/0x570
 ? clockevents_program_event+0x144/0x370
 do_syscall_64+0xf4/0x1560
 ? do_syscall_64+0x1d7/0x1560
 ? __lock_release.isra.0+0x59/0x170
 ? do_syscall_64+0x34/0x1560
 ? lockdep_hardirqs_on_prepare.part.0+0x9b/0x140
 ? do_syscall_64+0x34/0x1560
 ? trace_hardirqs_on+0x19/0x1a0
 ? do_syscall_64+0xab/0x1560
 ? clear_bhb_loop+0x30/0x80
 entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7f154f5728dc
Code: 1e fa 41 f7 c1 ff 0f 00 00 75 33 55 48 89 e5 41 54 41 89 cc 53 48 89 fb 48 85 ff 74 41 45 89 e2 48 89 df b8 09 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 7c 5b 41 5c 5d c3 0f 1f 80 00 00 00 00 48 8b
RSP: 002b:00007ffeb6ac04f0 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f154f5728dc
RDX: 0000000000000003 RSI: 0000000040800000 RDI: 0000000000000000
RBP: 00007ffeb6ac0500 R08: 000000000000000c R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000001
R13: 000000001ddac980 R14: 00007f154fa629c0 R15: 00007f154fa62940
 </TASK>
irq event stamp: 62665
hardirqs last  enabled at (62679): [<ffffffff9e1cd23e>] __up_console_sem+0x5e/0x70
hardirqs last disabled at (62698): [<ffffffff9e1cd223>] __up_console_sem+0x43/0x70
softirqs last  enabled at (62692): [<ffffffff9dfc5d01>] handle_softirqs+0x5c1/0x8b0
softirqs last disabled at (62721): [<ffffffff9dfc6152>] __irq_exit_rcu+0x152/0x280
---[ end trace 0000000000000000 ]---
scsi host74: TCM_Loopback