[PATCH 2/5] PCI/P2PDMA: Wait for RCU readers before freeing state

[Leon Romanovsky <leon@kernel.org>]

From: Leon Romanovsky <leonro@nvidia.com>

pci_p2pmem_find_many() scans all PCI devices without locking or
protection against driver unbind, including devices with poolless
P2PDMA state. pci_has_p2pmem() may observe pdev->p2pdma just before
driver unbind clears it, while pci_p2pdma_release() skips the grace
period when no pool is present. This allows devres to free the object
while it is still in use.

Clear the pointer with RCU_INIT_POINTER() and always wait for pre-existing
RCU readers before returning. The same grace period continues to protect
gen_pool users for pool-backed providers.

Cc: Alex Williamson <alex@shazbot.org>
Cc: Matt Evans <matt@ozlabs.org>
Fixes: 372d6d1b8ae3 ("PCI/P2PDMA: Refactor to separate core P2P functionality from memory allocation")
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Tested-by: Tushar Dave <tdave@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
 drivers/pci/p2pdma.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 8124bcebfa2d..52974809e1e1 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -236,9 +236,8 @@ static void pci_p2pdma_release(void *data)
 		return;
 
 	/* Flush and disable pci_alloc_p2p_mem() */
-	pdev->p2pdma = NULL;
-	if (p2pdma->pool)
-		synchronize_rcu();
+	RCU_INIT_POINTER(pdev->p2pdma, NULL);
+	synchronize_rcu();
 	xa_destroy(&p2pdma->map_types);
 
 	if (!p2pdma->pool)

-- 
2.55.0