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

[Uladzislau Rezki <urezki@gmail.com>]

On Mon, Oct 26, 2026 at 09:04:21AM -0700, Andrew Morton wrote:
> On Mon, 26 Oct 2026 11:25:03 +0100 "Uladzislau Rezki (Sony)" <urezki@gmail.com> 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@kernel.org>
> > Fixes: 04aa71da5f35 ("mm/vmalloc: do not trigger BUG() on BH disabled context")
> 
> Sounds like a cc:stable is needed?
> 
Yes. Should i resend and put cc:stable?

> > Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> > ---
> >  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.
> 
Yep. I checked before the kernel sources and saw that people use it
with WARN. I thought switching from BUG() to WARN() is better.

--
Uladzislau Rezki