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SubjectRe: [FIX] slub: Remove kmalloc under list_lock from list_slab_objects() V2
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On 2019/12/01 8:09, Andrew Morton wrote:
>> Perform the allocation in free_partial() before the list_lock is taken.
>
> No response here? It looks a lot simpler than the originally proposed
> patch?
>
>> --- linux.orig/mm/slub.c 2019-10-15 13:54:57.032655296 +0000
>> +++ linux/mm/slub.c 2019-11-11 15:52:11.616397853 +0000
>> @@ -3690,14 +3690,15 @@ error:
>> }
>>
>> static void list_slab_objects(struct kmem_cache *s, struct page *page,
>> - const char *text)
>> + const char *text, unsigned long *map)
>> {
>> #ifdef CONFIG_SLUB_DEBUG
>> void *addr = page_address(page);
>> void *p;
>> - unsigned long *map = bitmap_zalloc(page->objects, GFP_ATOMIC);

Changing from !(__GFP_IO | __GFP_FS) allocation to

>> +
>> if (!map)
>> return;
>> +
>> slab_err(s, page, text, s->name);
>> slab_lock(page);
>>
>> @@ -3723,6 +3723,11 @@ static void free_partial(struct kmem_cac
>> {
>> LIST_HEAD(discard);
>> struct page *page, *h;
>> + unsigned long *map = NULL;
>> +
>> +#ifdef CONFIG_SLUB_DEBUG
>> + map = bitmap_alloc(oo_objects(s->max), GFP_KERNEL);

__GFP_IO | __GFP_FS allocation.
How is this path guaranteed to be safe to perform __GFP_IO | __GFP_FS reclaim?

>> +#endif
>>
>> BUG_ON(irqs_disabled());
>> spin_lock_irq(&n->list_lock);

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