Re: [PATCH -v2] rmap: make anon_vma_prepare link in all the anon_vmasof a mergeable VMA

[Linus Torvalds]

On Wed, 7 Apr 2010, Rik van Riel wrote:
>
>  - fix the locking issues spotted by Kosaki Motohiro

No, they're broken.

And Rik, please explain the locking rather than make even more of these 
kinds of random ad-hoc locking rules.

I've said this now _three_ times, but let me repeat once more:

 - the locking rules for that anon_vma_chain are very unclear. I _think_ 
   you mean for them to be "mmap_sem held for writing, _or_ mmap_sem held 
   for reading and page_table_lock held", but nowhere is that actually 
   documented.

Why is it so hard for you to just admit that? Especially after you 
yourself got it wrong.

> +		merge_vma = find_mergeable_anon_vma(vma);
> +		if (merge_vma) {
> +			int ret;
> +			spin_lock(&mm->page_table_lock);
> +			ret = anon_vma_clone(vma, merge_vma);
> +			if (!ret)
> +				vma->anon_vma = merge_vma->anon_vma;
> +			spin_unlock(&mm->page_table_lock);
> +			return ret;
> +		}

Rik, the above is obviously total crap.

anon_vma_clone() needs to allocate memory, and it does so with GFP_KERNEL. 
You can't do that with a spinlock held.

		Linus
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/