From: Leon Romanovsky <[email protected]> pdev->p2pdma is normally accessed through provider-owned references, but pci_p2pmem_find_many() and the p2pmem sysfs attributes may race with driver unbind.
Document initialization, teardown, and how the release grace period protects both the P2PDMA state and its optional allocation pool. Cc: Alex Williamson <[email protected]> Cc: Matt Evans <[email protected]> Signed-off-by: Leon Romanovsky <[email protected]> --- drivers/pci/p2pdma.c | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c index 4e4d2df17a45..d8c9d605b828 100644 --- a/drivers/pci/p2pdma.c +++ b/drivers/pci/p2pdma.c @@ -21,6 +21,29 @@ #include <linux/seq_buf.h> #include <linux/xarray.h> +/* + * Lifetime and RCU usage + * + * Within one driver bind, pdev->p2pdma is set exactly once, + * by pcim_p2pdma_init(), and cleared exactly once, by the pci_p2pdma_release() + * devres action that the same function installs. It is never changed and follow + * same lifetime as parent pdev. + * + * Most exported entry points reach pdev->p2pdma through a struct pci_dev or a + * struct p2pdma_provider owned by the provider driver, and + * pcim_p2pdma_provider() requires callers to drop those references before the + * driver's remove() completes. Those cannot run concurrently with + * pci_p2pdma_release(), and their rcu_dereference() calls are simply how an + * __rcu pointer is read. + * + * pci_p2pmem_find_many() and the p2pmem sysfs attributes are the exceptions. + * The first walks every PCI device, so it can reach a provider whose driver is + * unbinding: pci_get_device() pins the struct pci_dev, not the driver. The + * second is reachable from userspace until sysfs_remove_group() runs at the end + * of the release. pci_has_p2pmem() must dereference the object to determine + * whether it owns a gen_pool, so even a device without a pool must remain alive + * until that RCU reader exits. + */ struct pci_p2pdma { struct gen_pool *pool; bool p2pmem_published; -- 2.55.0
