| Message ID | 20230209172953.4597-1-logang@deltatee.com (mailing list archive) |
|---|---|
| State | Accepted |
| Delegated to: | Bjorn Helgaas |
| Headers | show |
| Series | PCI/P2PDMA: Annotate RCU dereference | expand |
On 2/9/23 09:29, 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@intel.com> > Signed-off-by: Logan Gunthorpe <logang@deltatee.com> > --- I believe that this change removes the warning is question. With that said, looks good. Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com> -ck
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@intel.com> > Signed-off-by: Logan Gunthorpe <logang@deltatee.com> 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
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); }
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@intel.com> Signed-off-by: Logan Gunthorpe <logang@deltatee.com> --- Based on v6.2-rc7 drivers/pci/p2pdma.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) base-commit: 4ec5183ec48656cec489c49f989c508b68b518e3 -- 2.30.2