Re: mm, slab/slub: Ensure kmem_cache_alloc_bulk() is available early

[Thomas Gleixner <tglx@linutronix.de>]

On Thu, Feb 09 2023 at 20:28, Matthew Wilcox wrote:
> On Wed, Feb 08, 2023 at 09:46:30PM +0100, Thomas Gleixner wrote:
>> The issue is that there might be maple_tree users which depend on
>> GFP_ATOMIC, but call in from interrupt enabled context, which is
>> legitimate today.
>> 
>> Willy might have some insight on that.
>
> Not today, but eventually.  There are XArray users which modify the tree
> in interrupt context or under some other spinlock that we can't drop
> for them in order to do an allocation.  And I want to replace the radix
> tree underpinnings of the XArray with the maple tree.  In my copious
> spare time.

If any usage which you described, i.e. interrupt context or with a
spinlock held, where interrupts were disabled on acquisition of the
lock, ends up calling into kmem_cache_alloc_bulk() today, then that's
broken because kmem_cache_alloc_bulk() reenables interrupts
unconditionally.

So either such code does not exist as of today or it just gets lucky to
not run into the code path leading up to kmem_cache_alloc_bulk().

We have to clarify what the valid calling convention of
kmem_cache_alloc_bulk() is in the regular kernel context, i.e. outside
of early boot.

Thanks,

        tglx