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

[Uladzislau Rezki <urezki@gmail.com>]

On Tue, Oct 27, 2026 at 10:25:23AM +0000, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
> - [High] mm/vmalloc: ABBA deadlock when calling vmalloc() with BH or IRQs disabled
> - [Medium] mm/vmalloc: __get_vm_area_node() irq bailout triggers warnings and retry
> --
> 
> commit 9fea18279139941aa247a1a577dd5e101116871a
> Author: Uladzislau Rezki (Sony) <urezki@gmail.com>
> 
> mm/vmalloc: Bail out if in softirq context
> 
> This commit restores a softirq check in __get_vm_area_node() using
> in_serving_softirq() so that vmalloc() bails out when invoked from softirq
> context while still permitting callers with disabled bottom halves. It also
> replaces BUG_ON(in_nmi() || in_hardirq()) with a WARN_ON_ONCE() check that
> returns NULL.
> 
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index 44e0eb32708f1..5a949525b9db8 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -3271,7 +3271,13 @@ 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;
> 
> [Severity: High]
> Can allowing vmalloc() in task context with bottom halves or interrupts
> disabled still cause a multi-CPU ABBA deadlock on vmalloc's internal locks?
> 
CPU_0           CPU_1
 vmalloc()       lock(B)
  lock(A)         vmalloc()
   soft-irq        lock(A)
    lock(B)

Such callers have to be fixed at their call sites. __get_vm_area_node()
cannot detect ABBA deadlock which involves a lock held by a task-context
caller.

--
Uladzislau Rezki