Re: [PATCH] mm/vmalloc: Bail out if in softirq context

[Andrew Morton]

On Mon, 26 Oct 2026 11:25:03 +0100 "Uladzislau Rezki (Sony)" <urezki@xxxxxxxxx> wrote:

> vmalloc() is not allowed to be invoked from the NMI,
> hard-irq and softirq contexts because doing so may
> deadlock on internal locks.
> 
> Commit 04aa71da5f35 ("mm/vmalloc: do not trigger BUG()
> on BH disabled context") replaced the deprecated in_interrupt()
> macro with explicit in_nmi() and in_hardirq() checks, but
> unintentionally dropped the softirq context check.
> 
> Example:
> 
> <snip>
> vzalloc() in a task
>  spin_lock(&vn->busy.lock)
>   <------ Hard irq
>    irq_exit()
>     process softirq on the same CPU
>      vmalloc()
>       spin_lock(&vn->busy.lock)
>        spins forever
> <snip>
> 
> Restore the check by checking the caller's context with
> the in_serving_softirq() helper. Note that, it is still
> allowed to invoke vmalloc() with disabled bottom halves.
> 
> Replace BUG_ON() with WARN_ON_ONCE() for in_nmi() and
> in_hardirq() case.
> 
> Cc: David Hildenbrand (Arm) <david@xxxxxxxxxx>
> Fixes: 04aa71da5f35 ("mm/vmalloc: do not trigger BUG() on BH disabled context")

Sounds like a cc:stable is needed?

> Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
> ---
>  mm/vmalloc.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 7521b9b3bfd2..36e6e3be6ba4 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -3252,7 +3252,13 @@ struct vm_struct *__get_vm_area_node(unsigned long size,
>  	struct vm_struct *area;
>  	unsigned long requested_size = size;
>  
> -	BUG_ON(in_nmi() || in_hardirq());
> +	/* IRQ re-entrancy -> irq_exit() -> process softirq. */
> +	if (in_serving_softirq())
> +		return NULL;
> +
> +	if (WARN_ON_ONCE(in_nmi() || in_hardirq()))
> +		return NULL;

WARN does a lot of stuff and I rather doubt that it's all nmi-safe.  I
don't think this matters much - it'll probably work out and as long as
*something* gets printed, it did its job.

>  	size = ALIGN(size, 1ul << shift);
>  	if (unlikely(!size))
>  		return NULL;
> -- 
> 2.47.3