Re: [PATCH v2 3/5] mm: Add RCU-based VMA lookup helper that waits for writers

[Dave Hansen <dave.hansen@intel.com>]

On 6/10/26 16:04, Dave Hansen wrote:
> +	/* Slow path: preclude VMA writers by getting mmap read lock. */
> +	guard(rwsem_read)(&mm->mmap_lock);
> +	if (!vma_start_read_locked(vma))
> +		return NULL;

Welp, I actually ran and tested this, but it's got a big bug. The slow
path is broken. It needs:

	/* Slow path: preclude VMA writers by getting mmap read lock. */
	guard(rwsem_read)(&mm->mmap_lock);
+	vma = vma_lookup(mm, address);
	if (!vma_start_read_locked(vma))
		return NULL;

Because VMA is NULL in slow path otherwise. So it'll definitely need a
v3 or a fixup before it goes anywhere.