linux-kernel - Re: [PATCH] kasan: Don't call find_vm

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Message-ID: <CAPAsAGzk4h3B-LNQdedrk=2aRbPoOJeVv_tQF2QPgzwwUvirEw@mail.gmail.com>
Date: Wed, 12 Feb 2025 12:59:01 +0100
From: Andrey Ryabinin <ryabinin.a.a@...il.com>
To: Waiman Long <longman@...hat.com>
Cc: Alexander Potapenko <glider@...gle.com>, Andrey Konovalov <andreyknvl@...il.com>, 
	Dmitry Vyukov <dvyukov@...gle.com>, Vincenzo Frascino <vincenzo.frascino@....com>, 
	Andrew Morton <akpm@...ux-foundation.org>, 
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Clark Williams <clrkwllms@...nel.org>, 
	Steven Rostedt <rostedt@...dmis.org>, kasan-dev@...glegroups.com, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev, 
	Nico Pache <npache@...hat.com>
Subject: Re: [PATCH] kasan: Don't call find_vm_area() in RT kernel

On Tue, Feb 11, 2025 at 5:08 PM Waiman Long <longman@...hat.com> wrote:
> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> index 3fe77a360f1c..e1ee687966aa 100644
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -398,9 +398,20 @@ static void print_address_description(void *addr, u8 tag,
>                 pr_err("\n");
>         }
>
> -       if (is_vmalloc_addr(addr)) {
> -               struct vm_struct *va = find_vm_area(addr);
> +       if (!is_vmalloc_addr(addr))
> +               goto print_page;
>
> +       /*
> +        * RT kernel cannot call find_vm_area() in atomic context.
> +        * For !RT kernel, prevent spinlock_t inside raw_spinlock_t warning
> +        * by raising wait-type to WAIT_SLEEP.
> +        */
> +       if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
> +               static DEFINE_WAIT_OVERRIDE_MAP(vmalloc_map, LD_WAIT_SLEEP);
> +               struct vm_struct *va;
> +
> +               lock_map_acquire_try(&vmalloc_map);
> +               va = find_vm_area(addr);

Can we hide all this logic behind some function like
kasan_find_vm_area() which would return NULL for -rt?

>                 if (va) {
>                         pr_err("The buggy address belongs to the virtual mapping at\n"
>                                " [%px, %px) created by:\n"
> @@ -410,8 +421,13 @@ static void print_address_description(void *addr, u8 tag,
>
>                         page = vmalloc_to_page(addr);

Or does vmalloc_to_page() secretly take  some lock somewhere so we
need to guard it with this 'vmalloc_map' too?
So my suggestion above wouldn't be enough, if that's the case.

>                 }
> +               lock_map_release(&vmalloc_map);
> +       } else {
> +               pr_err("The buggy address %px belongs to a vmalloc virtual mapping\n",
> +                       addr);
>         }
>