Re: [PATCH v1] page_alloc: assert IRQs are enabled in heap alloc/free

[David Vrabel <dvrabel@xxxxxxxxxx>]

On 20/04/2022 07:26, Jan Beulich wrote:
> On 19.04.2022 17:01, David Vrabel wrote:
> > From: David Vrabel <dvrabel@xxxxxxxxxxxx>
> >
> > Heap pages can only be safely allocated and freed with interuupts
> > enabled as they may require a TLB flush which will send IPIs.
> >
> > Enhance the assertions in alloc_xenheap_pages() and
> > alloc_domheap_pages() to check interrupts are enabled. For consistency
> > the same asserts are used when freeing heap pages.
> >
> > As an exception, during early boot when only 1 PCPU is online,
> > allocations are permitted with interrupts disabled.
> This exception is tightly coupled with spin lock checking, i.e. the
> point in time when spin_debug_enable() is called. I think this wants
> making explicit at least in the code comment, but as a result I also
> wonder in how far the extended assertions are really worthwhile: Any
> violation would be detected in check_lock() anyway. Thoughts?
I was caught out by stop_machine_run() disabling both interrupts and 
spin lock debugging when running the action function, so check_lock() 
didn't help in this (admittedly) narrow use case.
> Furthermore I'm concerned of Arm not using either SYS_STATE_smp_boot
> or spin_debug_enable().
David