Re: [PATCH v2] kasan: remove kasan_find_vm_area() to prevent possible deadlock

[Uladzislau Rezki]

On Mon, Jul 14, 2025 at 08:27:40AM +0900, Byungchul Park wrote:
> On Sat, Jul 12, 2025 at 03:46:10PM +0000, Yeo Reum Yun wrote:
> > Hi ByungChul,
> > 
> > [...]
> > > I checked the critical section by &vn->busy.lock in find_vm_area().  The
> > > time complextity looks O(log N).  I don't think an irq disabled section
> > > of O(log N) is harmful.  I still think using
> > > spin_lock_irqsave(&vn->busy.lock) can resolve this issue with no worry
> > > of significant irq delay.  Am I missing something?
> > 
> > I don't agree for this.
> > since in PREEMPT_RT case, it has the same problem.
> > 
> > In case of PREEMPT_RT, spin_lock_irqsave() becomes rt_spin_lock() which is sleepable.
> > But, KASAN calls "rt_spin_lock()" holding raw_spin_lock_irqsave() which is definitely wrong.
> 
> It's another issue than irq handling latency, but it's about lock usage
> correctness.  You are right.
> 
There is vmalloc_dump_obj() function which should be used IMO:

<snip>
pr_err("The buggy address %px belongs to a vmalloc virtual mapping, dump it...\n", addr);
vmalloc_dump_obj(addr);
<snip>

we use trylock there to eliminate an issue if invoked from the IRQ
context.

--
Uladzislau Rezki