RE: [PATCH 1/1] arm: get task_stack reference before dump_backtrace

[Maninder Singh]

Hi,

> On Thu, Mar 05, 2026 at 12:35:27PM +0530, Maninder Singh wrote:
>> With Support of THREAD_INFO_IN_TASK, stack of task can be
>> freed earlier than task (even if task's reference is taken),
>> and it needs separate reference with try_get_task_stack()
>> before using the stack.
>> Otherwise if someone calls show_stack() for task, it can oops
>> the kernel like below: (Tried with normal race of show_stack when
>> task still exists, but its stack is freed)
> 
> Looking at x86, it also has THREAD_INFO_IN_TASK, but I see nothing like
> this in show_stack(). How come x86 isn't similarly buggy?
> 

Thanks for your inputs.

I sent patch for x86 also to report same issue, but no replies :)

https://lkml.org/lkml/2026/3/11/317

So I guess we will never know if it is buggy or not.
and why ARM64 has done the checkings and there is no need for x86 and ARM.

 
>> 8<--- cut here ---
>> Unable to handle kernel paging request at virtual address f8aebec4 when read
>> [f8aebec4] *pgd=83c2c811, *pte=00000000, *ppte=00000000
>> Internal error: Oops: 7 [#1] SMP ARM
>> ..
>> CPU: 0 UID: 0 PID: 70 Comm: cat Not tainted 7.0.0-rc2-next-20260302+ #26 VOLUNTARY
>> ..
>> PC is at __read_once_word_nocheck+0x0/0x8
>> LR is at unwind_frame+0x6b0/0xa90
>> ...
>> Call trace:
>>  __read_once_word_nocheck from unwind_frame+0x6b0/0xa90
>>  unwind_frame from unwind_backtrace+0x178/0x1e0
>>  unwind_backtrace from show_stack+0x10/0x14
>> ...
>>
>> ARM64 also takes care of it in dump_backtrace(), so same logic
>> is added for ARM also.
>>
>> Fixes: 18ed1c01a7dd ("ARM: smp: Enable THREAD_INFO_IN_TASK")
>> Signed-off-by: Maninder Singh <maninder1.s@xxxxxxxxxxx>


Thanks,
Maninder Singh