linux-kernel - Re: [PATCH v2] kasan: remove kasan_find_vm

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Message-ID: <CA+fCnZfq570HfXpS1LLUVm0sHXW+rpkSOMLVzafZ2q_ogha47g@mail.gmail.com>
Date: Thu, 3 Jul 2025 21:05:20 +0200
From: Andrey Konovalov <andreyknvl@...il.com>
To: Yeoreum Yun <yeoreum.yun@....com>
Cc: glider@...gle.com, dvyukov@...gle.com, vincenzo.frascino@....com, 
	akpm@...ux-foundation.org, bigeasy@...utronix.de, clrkwllms@...nel.org, 
	rostedt@...dmis.org, byungchul@...com, max.byungchul.park@...il.com, 
	ysk@...lloc.com, kasan-dev@...glegroups.com, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev, 
	Andrey Ryabinin <ryabinin.a.a@...il.com>
Subject: Re: [PATCH v2] kasan: remove kasan_find_vm_area() to prevent possible deadlock

On Thu, Jul 3, 2025 at 8:55 PM Yeoreum Yun <yeoreum.yun@....com> wrote:
>
> Hi Andrey,
>
> > >
> > > find_vm_area() couldn't be called in atomic_context.
> > > If find_vm_area() is called to reports vm area information,
> > > kasan can trigger deadlock like:
> > >
> > > 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!
> > >
> > > To prevent possible deadlock while kasan reports, remove kasan_find_vm_area().
> >
> > Can we keep it for when we are in_task()?
>
> We couldn't do. since when kasan_find_vm_area() is called,
> the report_lock is grabbed with irq disabled.
>
> Please check discuss with Andrey Ryabinin:
>   https://lore.kernel.org/all/4599f645-f79c-4cce-b686-494428bb9e2a@gmail.com/

That was about checking for !in_interrupt(), but I believe checking
for in_task() is different? But I'm not an expert on these checks.