Re: [PATCH RFC] m68k: skip kernel premption if interrupts were disabled

[Michael Schmitz <schmitzmic@gmail.com>]

Hi Finn,

thanks - that should suffice.

Tests on the slower ARAnyM instance also passed OK. Leaves test on 030 - 
I'll see whether I can find an earlier kernel version with a smaller 
memory footprint to test these patches on.

Now none of this has got us any closer to a solution for the spinlock 
recursion bug...

Cheers,

	Michael

Am 27.03.2024 um 16:50 schrieb Finn Thain:
>
> On Wed, 27 Mar 2024, Michael Schmitz wrote:
>
>> it might be easier for Geert to merge the two patches (or a single one)
>> on top of his preempt branch if they come in the usual git format.
>
> I suppose that would be easier, assuming it doesn't need a lot of rework.
> Anyway, here's the diff.
>
> diff --git a/arch/m68k/mm/motorola.c b/arch/m68k/mm/motorola.c
> index c1761d309fc6..d0092a3127c0 100644
> --- a/arch/m68k/mm/motorola.c
> +++ b/arch/m68k/mm/motorola.c
> @@ -15,6 +15,7 @@
>  #include <linux/mm.h>
>  #include <linux/swap.h>
>  #include <linux/kernel.h>
> +#include <linux/preempt.h>
>  #include <linux/string.h>
>  #include <linux/types.h>
>  #include <linux/init.h>
> @@ -139,10 +140,14 @@ void __init init_pointer_table(void *table, int type)
>
>  void *get_pointer_table(int type)
>  {
> -	ptable_desc *dp = ptable_list[type].next;
> -	unsigned int mask = list_empty(&ptable_list[type]) ? 0 : PD_MARKBITS(dp);
> +	ptable_desc *dp;
> +	unsigned int mask;
>  	unsigned int tmp, off;
>
> +	preempt_disable();
> +
> +	dp = ptable_list[type].next;
> +	mask = list_empty(&ptable_list[type]) ? 0 : PD_MARKBITS(dp);
>  	/*
>  	 * For a pointer table for a user process address space, a
>  	 * table is taken from a page allocated for the purpose.  Each
> @@ -153,9 +158,13 @@ void *get_pointer_table(int type)
>  		void *page;
>  		ptable_desc *new;
>
> +		sched_preempt_enable_no_resched();
> +
>  		if (!(page = (void *)get_zeroed_page(GFP_KERNEL)))
>  			return NULL;
>
> +		preempt_disable();
> +
>  		if (type == TABLE_PTE) {
>  			/*
>  			 * m68k doesn't have SPLIT_PTE_PTLOCKS for not having
> @@ -170,6 +179,7 @@ void *get_pointer_table(int type)
>  		PD_MARKBITS(new) = ptable_mask(type) - 1;
>  		list_add_tail(new, dp);
>
> +		sched_preempt_enable_no_resched();
>  		return (pmd_t *)page;
>  	}
>
> @@ -180,6 +190,7 @@ void *get_pointer_table(int type)
>  		/* move to end of list */
>  		list_move_tail(dp, &ptable_list[type]);
>  	}
> +	sched_preempt_enable_no_resched();
>  	return page_address(PD_PAGE(dp)) + off;
>  }
>
> @@ -190,6 +201,8 @@ int free_pointer_table(void *table, int type)
>  	unsigned long page = ptable & PAGE_MASK;
>  	unsigned int mask = 1U << ((ptable - page)/ptable_size(type));
>
> +	preempt_disable();
> +
>  	dp = PD_PTABLE(page);
>  	if (PD_MARKBITS (dp) & mask)
>  		panic ("table already free!");
> @@ -203,6 +216,7 @@ int free_pointer_table(void *table, int type)
>  		if (type == TABLE_PTE)
>  			pagetable_pte_dtor(virt_to_ptdesc((void *)page));
>  		free_page (page);
> +		sched_preempt_enable_no_resched();
>  		return 1;
>  	} else if (ptable_list[type].next != dp) {
>  		/*
> @@ -211,6 +225,7 @@ int free_pointer_table(void *table, int type)
>  		 */
>  		list_move(dp, &ptable_list[type]);
>  	}
> +	sched_preempt_enable_no_resched();
>  	return 0;
>  }
>
>