Re: BUG: kernel NULL pointer dereference, address: 00 - ida_free+0x76/0x140

[Naresh Kamboju]

> > > I did already let Greg know when he emailed us on backporting the
> > > patch to stable, and he acked saying he removed them. So as long as
> > > these are not in the queue for 5.6 (it is not in Linus' tree yet), we
> > > should be good.
> >
> > The reported bug is still noticed on Linux mainline master branch
> > The Kernel BUG noticed on x86_64 and i386 running selftest on Linux
> > mainline kernel 5.6.0.
>
> Oh sorry, I thought that this patch was dropped from the maintainer's
> for-next branch.
>
> Heikki, what do you think about my suggestion of having kobject
> deallocate its children?
>
> In the meantime, are people cool with the patch that Heikki proposed
> as a temporary mitigation? I think my solution might be a bit more
> involved. If I don't hear anything back, I will send out Heikki's
> suggestion as a patch.

This reported problem still noticed on 5.7.0-rc1

Test crash log:
-------------------
[  281.822463] BUG: kernel NULL pointer dereference, address: 00000000
[  281.829543] #PF: supervisor read access in kernel mode
[  281.834680] #PF: error_code(0x0000) - not-present page
[  281.839820] *pde = 00000000
[  281.842706] Oops: 0000 [#1] SMP
[  281.845852] CPU: 1 PID: 3998 Comm: modprobe Tainted: G        W
    5.7.0-rc1 #1
[  281.853590] Hardware name: Supermicro SYS-5019S-ML/X11SSH-F, BIOS
2.0b 07/27/2017
[  281.861063] EIP: ida_free+0x61/0x130
[  281.864641] Code: 00 c7 45 e8 00 00 00 00 c7 45 ec 00 00 00 00 0f
88 c4 00 00 00 89 d3 e8 0d 8e 87 00 89 c7 8d 45 d8 e8 93 1e 01 00 a8
01 75 3f <0f> a3 30 72 72 8b 45 d8 89 fa e8 e0 8f 87 00 53 68 08 ab fd
de e8
[  281.883395] EAX: 00000000 EBX: 00000000 ECX: e422d8c0 EDX: 00000000
[  281.889672] ESI: 00000000 EDI: 00000246 EBP: e5d63cdc ESP: e5d63cb0
[  281.895935] DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068 EFLAGS: 00010046
[  281.902720] CR0: 80050033 CR2: 00000000 CR3: 1db85000 CR4: 003406d0
[  281.908978] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
[  281.915243] DR6: fffe0ff0 DR7: 00000400
[  281.919073] Call Trace:
[  281.921521]  software_node_release+0x21/0x80
[  281.925792]  kobject_put+0xa8/0x1c0
[  281.929284]  kobject_del+0x40/0x60
[  281.932680]  kobject_put+0x92/0x1c0
[  281.936165]  fwnode_remove_software_node+0x30/0x50
[  281.940957]  software_node_unregister_nodes+0x2b/0x50
[  281.946002]  test_printf_init+0xe00/0x1d29 [test_printf]
[  281.951320]  ? fs_reclaim_acquire.part.121+0x5/0x30
[  281.956202]  ? test_hashed+0x54/0x54 [test_printf]
[  281.960985]  ? test_hashed+0x54/0x54 [test_printf]
[  281.965770]  do_one_initcall+0x54/0x2e0
[  281.969639]  ? rcu_read_lock_sched_held+0x47/0x70
[  281.974366]  ? kmem_cache_alloc_trace+0x285/0x2b0
[  281.979063]  ? do_init_module+0x21/0x1f7
[  281.982982]  ? do_init_module+0x21/0x1f7
[  281.986899]  do_init_module+0x50/0x1f7
[  281.990659]  load_module+0x1e32/0x2540
[  281.994410]  __ia32_sys_finit_module+0x8f/0xe0
[  281.998854]  do_fast_syscall_32+0x7f/0x330
[  282.002949]  entry_SYSENTER_32+0xaa/0x102
[  282.006952] EIP: 0xb7f07ce1
[  282.009742] Code: 5e 5d c3 8d b6 00 00 00 00 b8 40 42 0f 00 eb c1
8b 04 24 c3 8b 1c 24 c3 8b 34 24 c3 8b 3c 24 c3 90 51 52 55 89 e5 0f
34 cd 80 <5d> 5a 59 c3 90 90 90 90 8d 76 00 58 b8 77 00 00 00 cd 80 90
8d 76
[  282.028480] EAX: ffffffda EBX: 00000005 ECX: 0806233a EDX: 00000000
[  282.034739] ESI: 099fe840 EDI: 099fe570 EBP: 099fe700 ESP: bf97146c
[  282.040994] DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 007b EFLAGS: 00000292
[  282.047776] Modules linked in: test_printf(+) cls_bpf sch_fq 8021q
sch_ingress veth algif_hash x86_pkg_temp_thermal fuse [last unloaded:
gpio_mockup]
[  282.061155] CR2: 0000000000000000
[  282.064472] ---[ end trace 09f43fd7981266c9 ]---
[  282.069084] EIP: ida_free+0x61/0x130

https://lkft.validation.linaro.org/scheduler/job/1362555#L7962

- Naresh