Re: [PATCH 0/3] kasan: memorize and print call_rcu stack

[Qian Cai]

> On May 6, 2020, at 1:19 AM, Walter Wu <walter-zh.wu@xxxxxxxxxxxx> wrote:
> 
> This patchset improves KASAN reports by making them to have
> call_rcu() call stack information. It is helpful for programmers
> to solve use-after-free or double-free memory issue.
> 
> The KASAN report was as follows(cleaned up slightly):
> 
> BUG: KASAN: use-after-free in kasan_rcu_reclaim+0x58/0x60
> 
> Freed by task 0:
> save_stack+0x24/0x50
> __kasan_slab_free+0x110/0x178
> kasan_slab_free+0x10/0x18
> kfree+0x98/0x270
> kasan_rcu_reclaim+0x1c/0x60
> rcu_core+0x8b4/0x10f8
> rcu_core_si+0xc/0x18
> efi_header_end+0x238/0xa6c
> 
> First call_rcu() call stack:
> save_stack+0x24/0x50
> kasan_record_callrcu+0xc8/0xd8
> call_rcu+0x190/0x580
> kasan_rcu_uaf+0x1d8/0x278
> 
> Last call_rcu() call stack:
> (stack is not available)
> 
> 
> Add new CONFIG option to record first and last call_rcu() call stack
> and KASAN report prints two call_rcu() call stack.
> 
> This option doesn't increase the cost of memory consumption. It is
> only suitable for generic KASAN.

I donât understand why this needs to be a Kconfig option at all. If call_rcu() stacks are useful in general, then just always gather those information. How do developers judge if they need to select this option or not?