Re: [PATCH 5/6] pci/p2pdma: Track pgmap references per resource, not globally
Thanks Dan, this is great. I think the changes in this series are
cleaner and more understandable than the patch set I had sent earlier.
However, I found a couple minor issues with this patch:
On 2019-03-29 9:27 a.m., Dan Williams wrote:
static void pci_p2pdma_release(void *data)
{
struct pci_dev *pdev = data;
@@ -103,12 +110,12 @@ static void pci_p2pdma_release(void *data)
if (!pdev->p2pdma)
return;
- wait_for_completion(&pdev->p2pdma->devmap_ref_done);
- percpu_ref_exit(&pdev->p2pdma->devmap_ref);
+ /* Flush and disable pci_alloc_p2p_mem() */
+ pdev->p2pdma = NULL;
+ synchronize_rcu();
gen_pool_destroy(pdev->p2pdma->pool);
I missed this on my initial review, but it became obvious when I tried
to test the series: this is a NULL dereference seeing pdev->p2pdma was
set to NULL a few lines up.
When I fix this by storing p2pdma in a local variable, the patch set
works and never seems to crash when I hot remove p2pdma memory.
void *pci_alloc_p2pmem(struct pci_dev *pdev, size_t size)
{
- void *ret;
+ void *ret = NULL;
+ struct percpu_ref *ref;
+ rcu_read_lock();
if (unlikely(!pdev->p2pdma))
- return NULL;
Using RCU here makes sense to me, however I expect we should be using
the proper rcu_assign_pointer(), rcu_dereference() and __rcu tag with
pdev->p2pdma. If only to better document what's being protected with the
new RCU calls.
Logan