Re: [PATCH] mm/vmalloc: do not warn on -ENOMEM from va_clip() in pcpu_get_vm_areas()

[Uladzislau Rezki]

On Fri, Sep 25, 2026 at 03:15:00PM -0700, Andrew Morton wrote:
> On Fri, 25 Sep 2026 21:54:49 +0100 Palla Raghunath <raghunathpalla.0209@xxxxxxxxx> wrote:
> 
> > When pcpu_get_vm_areas() has to split a free vmap_area in the middle
> > (NE_FIT_TYPE), va_clip() needs an extra vmap_area object. It takes the
> > per-cpu ne_fit_preload_node if one is there, and otherwise falls back
> > to kmem_cache_alloc(GFP_NOWAIT), which may fail and return -ENOMEM.
> > pcpu_get_vm_areas() never preloads, and a single call can do more than
> > one such split: on a NUMA system it places one area per node group, so
> > the first split consumes the preloaded object and the next one depends
> > on the GFP_NOWAIT allocation.
> > 
> > That failure is expected and already handled: the recovery path returns
> > the areas clipped so far to the free tree, purges lazily freed areas and
> > retries. But the error is checked with WARN_ON_ONCE(), so a transient
> > allocation failure under memory pressure or fault injection triggers a
> > kernel warning, and a panic with panic_on_warn. syzbot hit this on a
> > two-node VM while creating a per-cpu BPF array map.
> > 
> > Keep the WARN_ON_ONCE() for errors other than -ENOMEM, which do indicate
> > a bug, and take the recovery path either way. This matches what commit
> > b9183788a2de ("mm/vmalloc: do not warn on -ENOMEM from va_alloc()") did
> > for the other va_clip() caller.
> > 
> > Fixes: 1b23ff80b399 ("mm/vmalloc: invoke classify_va_fit_type() in adjust_va_to_fit_type()")
> > Reported-by: syzbot+442828bb356b10813a47@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Closes: https://syzkaller.appspot.com/bug?extid=442828bb356b10813a47
> 
> I assume sysbot hit this via fault injection.    The report doesn't make this
> info easily available.  Or maybe it wasn't fault injection.
> 
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -5107,9 +5107,14 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
> >  
> >  		ret = va_clip(&free_vmap_area_root,
> >  			&free_vmap_area_list, va, start, size);
> > -		if (WARN_ON_ONCE(unlikely(ret)))
> > -			/* It is a BUG(), but trigger recovery instead. */
> > +		if (unlikely(ret)) {
> > +			/*
> > +			 * -ENOMEM from the GFP_NOWAIT fallback is expected.
> > +			 * Anything else is a BUG(), but trigger recovery instead.
> > +			 */
> > +			WARN_ON_ONCE(ret != -ENOMEM);
> 
> Look good.
> 
> The WARN_ON_ONCE() is potentially redundant.  We could make va_clip()
> remove __GFP_NOWARN from its kmem_cache_alloc() and let the page
> allocator do the warn for us.  Doesn't matter.
> 
The patch looks good to me also:

Reviewed-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>

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Uladzislau Rezki