Re: [PATCH] kasan: don't call find_vm_area() in in_interrupt() for possible deadlock

[Andrey Ryabinin <ryabinin.a.a@gmail.com>]

On 7/1/25 10:35 PM, Yeoreum Yun wrote:

FYI some of email addresses in CC look corrupted, e.g. "kpm@linux-foundation.org", "nd@arm.com"

> In below senario, kasan causes deadlock while reporting vm area informaion:
> 
> CPU0                                CPU1
> vmalloc();
>  alloc_vmap_area();
>   spin_lock(&vn->busy.lock)
>                                     spin_lock_bh(&some_lock);
>    <interrupt occurs>
>    <in softirq>
>    spin_lock(&some_lock);
>                                     <access invalid address>
>                                     kasan_report();
>                                      print_report();
>                                       print_address_description();
>                                        kasan_find_vm_area();
>                                         find_vm_area();
>                                          spin_lock(&vn->busy.lock) // deadlock!
> 
...

> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> index 8357e1a33699..61c590e8005e 100644
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -387,7 +387,7 @@ static inline struct vm_struct *kasan_find_vm_area(void *addr)
>  	static DEFINE_WAIT_OVERRIDE_MAP(vmalloc_map, LD_WAIT_SLEEP);
>  	struct vm_struct *va;
> 
> -	if (IS_ENABLED(CONFIG_PREEMPT_RT))
> +	if (IS_ENABLED(CONFIG_PREEMPT_RT) || in_interrupt())

in_interrupt() returns true if BH disabled, so this indeed should avoid the deadlock.
However, it seems we have similar problem with 'spin_lock_irq[save](&some_lock)' case and
in_interrupt() check doesn't fix it.

And adding irqs_disabled() check wouldn't make sense because print_report() always
 runs with irqs disabled.

I see no obvious way to fix this rather than remove find_vm_area() call completely and just
print less info.