Re: [PATCH v2 1/2] maple_tree: Disable mas_wr_append() when other readers are possible

[Christophe Leroy]

Le 12/09/2023 à 19:02, Christophe Leroy a écrit :
> 
> 
> Le 12/09/2023 à 18:49, Paul E. McKenney a écrit :
>> On Tue, Sep 12, 2023 at 11:44:23AM -0400, Liam R. Howlett wrote:
>>>> So my question is why is it useful to setup interrupts that early, given
>>>> that interrupts cannot possibly happen until the boot CPU enables them?
>>>
>>> I don't know for sure, but there are 'preallocated IRQs' which end up
>>> grouped 0-15, then I see another one added at 55 after the mpic console
>>> output.  I suspect it's so that they can be added as they are discovered
>>> during early boot?
>>
>> Christophe argues that the interrupt stacks must be allocated early
>> on, and that this acquires a mutex.
>>
> 
> Well, we can probably allocate them later than it is today.
> 
> In commit 547db12fd8a0 ("powerpc/32: Use vmapped stacks for interrupts")
> I already pushed the allocation at a later stage than it initialy was.
> 
> We can probably do it later if it helps, however it definitely needs to
> be done before enabling IRQs for obvious reasons, so it is a problem
> that alloc_vm_stack() calling __vmalloc_node() enables IRQs.

For FWIW, looks like arm32 is doing similar so the problem is likely to 
happen for them too. For that both CONFIG_IRQSTACKS and 
CONFIG_VMAP_STACK must be set it seems.

Christophe