Kernel oops with 6.14 when enabling TLS

[Hannes Reinecke]

On 3/4/25 20:44, Vlastimil Babka wrote:
> On 3/4/25 20:39, Hannes Reinecke wrote:
>> On 3/4/25 19:05, Matthew Wilcox wrote:
>>> On Tue, Mar 04, 2025 at 04:53:09PM +0000, Matthew Wilcox wrote:
>>>> Right, that's what happened in the block layer.  We mark the bio with
>>>> BIO_PAGE_PINNED if the pincount needs to be dropped.  As a transitional
>>>> period, we had BIO_PAGE_REFFED which indicated that the page refcount
>>>> needed to be dropped.  Perhaps there's something similar that network
>>>> could be doing.
>>>
>>> Until that time ... how does this look as a quick hack to avoid
>>> reverting the slab change?
>>>
>>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>>> index d6fed25243c3..ca08a923ac6d 100644
>>> --- a/include/linux/mm.h
>>> +++ b/include/linux/mm.h
>>> @@ -1520,7 +1520,10 @@ static inline void folio_get(struct folio *folio)
>>>    
>>>    static inline void get_page(struct page *page)
>>>    {
>>> -	folio_get(page_folio(page));
>>> +	struct folio *folio = page_folio(page);
>>> +	if (WARN_ON_ONCE(folio_test_slab(folio)))
>>> +		return;
>>> +	folio_get(folio);
>>>    }
>>>    
>>>    static inline __must_check bool try_get_page(struct page *page)
>>> @@ -1614,6 +1617,8 @@ static inline void put_page(struct page *page)
>>>    {
>>>    	struct folio *folio = page_folio(page);
>>>    
>>> +	if (folio_test_slab(folio))
>>> +		return;
>>>    	folio_put(folio);
>>>    }
>>>    
>>> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
>>> index 65f550cb5081..8c7fdb7d8c8f 100644
>>> --- a/lib/iov_iter.c
>>> +++ b/lib/iov_iter.c
>>> @@ -1190,8 +1190,12 @@ static ssize_t __iov_iter_get_pages_alloc(struct iov_iter *i,
>>>    		if (!n)
>>>    			return -ENOMEM;
>>>    		p = *pages;
>>> -		for (int k = 0; k < n; k++)
>>> -			get_page(p[k] = page + k);
>>> +		for (int k = 0; k < n; k++) {
>>> +			struct folio *folio = page_folio(page);
>>> +			p[k] = page + k;
>>> +			if (!folio_test_slab(folio))
>>> +				folio_get(folio);
>>> +		}
>>>    		maxsize = min_t(size_t, maxsize, n * PAGE_SIZE - *start);
>>>    		i->count -= maxsize;
>>>    		i->iov_offset += maxsize;
>>>
>>
>> Good news and bad news ...
>> Good news: TLS works again!
>> Bad news: no errors.
> 
> Wait, did you add a WARN_ON_ONCE() to the put_page() as I suggested? If yes
> and there was no error, it would have to be leaking the page. Or the path
> uses folio_put() and we'd need to put the warning there.
> 
Oh, no, I didn't. Just added the WARN_ON to get_page().
Let me try ...

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare at suse.de                                +49 911 74053 688
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