On Thu, Feb 09, 2023 at 10:29:53AM -0700, Logan Gunthorpe wrote:
> A dereference of the __rcu pointer was noticed by sparse:
>
> drivers/pci/p2pdma.c:199:44: sparse: sparse: dereference of noderef expression
>
> The __rcu pointer should be dereferenced using
> rcu_dereference_protected() instead of accessed directly. Its safe
> to use rcu_derference_protected() seeing a reference is held on
> the pgmap's percpu reference counter and thus it cannot disappear.
>
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
Applied with Chaitanya's reviewed-by to pci/p2pdma for v6.3, thanks!
> ---
>
> Based on v6.2-rc7
>
> drivers/pci/p2pdma.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index 86812d2073ea..9e8205572830 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -194,11 +194,13 @@ static const struct attribute_group p2pmem_group = {
> static void p2pdma_page_free(struct page *page)
> {
> struct pci_p2pdma_pagemap *pgmap = to_p2p_pgmap(page->pgmap);
> + /* safe to dereference while a reference is held to the percpu ref */
> + struct pci_p2pdma *p2pdma =
> + rcu_dereference_protected(pgmap->provider->p2pdma, 1);
> struct percpu_ref *ref;
>
> - gen_pool_free_owner(pgmap->provider->p2pdma->pool,
> - (uintptr_t)page_to_virt(page), PAGE_SIZE,
> - (void **)&ref);
> + gen_pool_free_owner(p2pdma->pool, (uintptr_t)page_to_virt(page),
> + PAGE_SIZE, (void **)&ref);
> percpu_ref_put(ref);
> }
>
>
> base-commit: 4ec5183ec48656cec489c49f989c508b68b518e3
> --
> 2.30.2
