Re: [BUG] WARNING in __alloc_frozen_pages_noprof

[Namhyung Kim <namhyung@kernel.org>]

Hello,

On Wed, Nov 26, 2025 at 12:19:21PM +0100, Peter Zijlstra wrote:
> On Wed, Nov 26, 2025 at 10:46:38AM +0100, Vlastimil Babka wrote:
> > +CC perf people as AFAIU the problem originates there. Should the limit
> > be lowered, or the allocations e.g. switched to kvmalloc, to avoid
> > requesting impossibly high order allocations?
> > 
> >         /*
> >          * There are several places where we assume that the order value is sane
> >          * so bail out early if the request is out of bound.
> >          */
> >         if (WARN_ON_ONCE_GFP(order > MAX_PAGE_ORDER, gfp))
> >                 return NULL;
> > 
> > 
> > 
> > On 11/19/25 10:07 AM, Xianying Wang wrote:
> > > Hi,
> > > 
> > > I hit the following warning in the page allocator when opening a perf
> > > event with callchain sampling after increasing
> > > kernel.perf_event_max_stack.This warning can be triggered by first
> > > writing a large value into kernel.perf_event_max_stack and then
> > > opening a perf event with callchain sampling enabled.
> > > 
> > > The reproducer does two things:
> > > 
> > > 1) It writes a large (but still accepted) value to the sysctl:
> > > 
> > > echo 0x40132 > /proc/sys/kernel/perf_event_max_stack
> > > 
> 
> Yeah, that is far too large. I suppose the actual max is somewhere near
> 8k, which would give 64k data for just the callchain -- given that a
> single perf buffer entry is limited to 64k (IIRC) and all that.

Right, we have u16 size in struct perf_event_header.

Thanks,
Namhyung