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SubjectRe: [PATCH] PCI/P2PDMA: finish RCU conversion of pdev->p2pdma
On Thu, Jul 01, 2021 at 02:56:21AM -0700, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.com>
>
> While looking at pci_alloc_p2pmem() I found rcu protection
> was not properly applied there, as pdev->p2pdma was
> potentially read multiple times.
>
> I decided to fix pci_alloc_p2pmem(), add __rcu qualifier
> to p2pdma field of struct pci_dev, and fix all
> other accesses to this field with proper rcu verbs.
>
> Fixes: 1570175abd16 ("PCI/P2PDMA: track pgmap references per resource, not globally")
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Applied to pci/p2pdma for v5.14, thanks!

There were some conflicting changes, so it'd be great if you could
take a look and see if I did the right thing:

https://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git/commit/?h=pci/p2pdma&id=651b0ba3f8302e183277e4fa317fff2f9685bca2

> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Ira Weiny <ira.weiny@intel.com>
> Cc: Logan Gunthorpe <logang@deltatee.com>
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: "Jérôme Glisse" <jglisse@redhat.com>
> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> Cc: linux-pci@vger.kernel.org
> ---
> drivers/pci/p2pdma.c | 101 ++++++++++++++++++++++++++++++-------------
> include/linux/pci.h | 2 +-
> 2 files changed, 73 insertions(+), 30 deletions(-)
>
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index 1963826303631465da2956b0e3abcec3e0fcfbc4..89095aa5c674f5b8237d543c7af2bbdc2c176e5a 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -48,10 +48,14 @@ static ssize_t size_show(struct device *dev, struct device_attribute *attr,
> char *buf)
> {
> struct pci_dev *pdev = to_pci_dev(dev);
> + struct pci_p2pdma *p2pdma;
> size_t size = 0;
>
> - if (pdev->p2pdma->pool)
> - size = gen_pool_size(pdev->p2pdma->pool);
> + rcu_read_lock();
> + p2pdma = rcu_dereference(pdev->p2pdma);
> + if (p2pdma && p2pdma->pool)
> + size = gen_pool_size(p2pdma->pool);
> + rcu_read_unlock();
>
> return scnprintf(buf, PAGE_SIZE, "%zd\n", size);
> }
> @@ -61,10 +65,14 @@ static ssize_t available_show(struct device *dev, struct device_attribute *attr,
> char *buf)
> {
> struct pci_dev *pdev = to_pci_dev(dev);
> + struct pci_p2pdma *p2pdma;
> size_t avail = 0;
>
> - if (pdev->p2pdma->pool)
> - avail = gen_pool_avail(pdev->p2pdma->pool);
> + rcu_read_lock();
> + p2pdma = rcu_dereference(pdev->p2pdma);
> + if (p2pdma && p2pdma->pool)
> + avail = gen_pool_avail(p2pdma->pool);
> + rcu_read_unlock();
>
> return scnprintf(buf, PAGE_SIZE, "%zd\n", avail);
> }
> @@ -74,9 +82,16 @@ static ssize_t published_show(struct device *dev, struct device_attribute *attr,
> char *buf)
> {
> struct pci_dev *pdev = to_pci_dev(dev);
> + struct pci_p2pdma *p2pdma;
> + bool published = false;
> +
> + rcu_read_lock();
> + p2pdma = rcu_dereference(pdev->p2pdma);
> + if (p2pdma)
> + published = p2pdma->p2pmem_published;
> + rcu_read_unlock();
>
> - return scnprintf(buf, PAGE_SIZE, "%d\n",
> - pdev->p2pdma->p2pmem_published);
> + return scnprintf(buf, PAGE_SIZE, "%d\n", published);
> }
> static DEVICE_ATTR_RO(published);
>
> @@ -95,8 +110,9 @@ static const struct attribute_group p2pmem_group = {
> static void pci_p2pdma_release(void *data)
> {
> struct pci_dev *pdev = data;
> - struct pci_p2pdma *p2pdma = pdev->p2pdma;
> + struct pci_p2pdma *p2pdma;
>
> + p2pdma = rcu_dereference_protected(pdev->p2pdma, 1);
> if (!p2pdma)
> return;
>
> @@ -128,16 +144,14 @@ static int pci_p2pdma_setup(struct pci_dev *pdev)
> if (error)
> goto out_pool_destroy;
>
> - pdev->p2pdma = p2p;
> -
> error = sysfs_create_group(&pdev->dev.kobj, &p2pmem_group);
> if (error)
> goto out_pool_destroy;
>
> + rcu_assign_pointer(pdev->p2pdma, p2p);
> return 0;
>
> out_pool_destroy:
> - pdev->p2pdma = NULL;
> gen_pool_destroy(p2p->pool);
> out:
> devm_kfree(&pdev->dev, p2p);
> @@ -159,6 +173,7 @@ int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar, size_t size,
> {
> struct pci_p2pdma_pagemap *p2p_pgmap;
> struct dev_pagemap *pgmap;
> + struct pci_p2pdma *p2pdma;
> void *addr;
> int error;
>
> @@ -200,7 +215,8 @@ int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar, size_t size,
> goto pgmap_free;
> }
>
> - error = gen_pool_add_owner(pdev->p2pdma->pool, (unsigned long)addr,
> + p2pdma = rcu_dereference_protected(pdev->p2pdma, 1);
> + error = gen_pool_add_owner(p2pdma->pool, (unsigned long)addr,
> pci_bus_address(pdev, bar) + offset,
> range_len(&pgmap->range), dev_to_node(&pdev->dev),
> pgmap->ref);
> @@ -476,6 +492,7 @@ upstream_bridge_distance(struct pci_dev *provider, struct pci_dev *client,
> int *dist, bool *acs_redirects, struct seq_buf *acs_list)
> {
> enum pci_p2pdma_map_type map_type;
> + struct pci_p2pdma *p2pdma;
>
> map_type = __upstream_bridge_distance(provider, client, dist,
> acs_redirects, acs_list);
> @@ -486,10 +503,12 @@ upstream_bridge_distance(struct pci_dev *provider, struct pci_dev *client,
> map_type = PCI_P2PDMA_MAP_NOT_SUPPORTED;
> }
>
> - if (provider->p2pdma)
> - xa_store(&provider->p2pdma->map_types, map_types_idx(client),
> - xa_mk_value(map_type), GFP_KERNEL);
> -
> + rcu_read_lock();
> + p2pdma = rcu_dereference(provider->p2pdma);
> + if (p2pdma)
> + xa_store(&p2pdma->map_types, map_types_idx(client),
> + xa_mk_value(map_type), GFP_ATOMIC);
> + rcu_read_unlock();
> return map_type;
> }
>
> @@ -595,7 +614,15 @@ EXPORT_SYMBOL_GPL(pci_p2pdma_distance_many);
> */
> bool pci_has_p2pmem(struct pci_dev *pdev)
> {
> - return pdev->p2pdma && pdev->p2pdma->p2pmem_published;
> + struct pci_p2pdma *p2pdma;
> + bool res;
> +
> + rcu_read_lock();
> + p2pdma = rcu_dereference(pdev->p2pdma);
> + res = p2pdma && p2pdma->p2pmem_published;
> + rcu_read_unlock();
> +
> + return res;
> }
> EXPORT_SYMBOL_GPL(pci_has_p2pmem);
>
> @@ -675,6 +702,7 @@ void *pci_alloc_p2pmem(struct pci_dev *pdev, size_t size)
> {
> void *ret = NULL;
> struct percpu_ref *ref;
> + struct pci_p2pdma *p2pdma;
>
> /*
> * Pairs with synchronize_rcu() in pci_p2pdma_release() to
> @@ -682,16 +710,17 @@ void *pci_alloc_p2pmem(struct pci_dev *pdev, size_t size)
> * read-lock.
> */
> rcu_read_lock();
> - if (unlikely(!pdev->p2pdma))
> + p2pdma = rcu_dereference(pdev->p2pdma);
> + if (unlikely(!p2pdma))
> goto out;
>
> - ret = (void *)gen_pool_alloc_owner(pdev->p2pdma->pool, size,
> + ret = (void *)gen_pool_alloc_owner(p2pdma->pool, size,
> (void **) &ref);
> if (!ret)
> goto out;
>
> if (unlikely(!percpu_ref_tryget_live(ref))) {
> - gen_pool_free(pdev->p2pdma->pool, (unsigned long) ret, size);
> + gen_pool_free(p2pdma->pool, (unsigned long) ret, size);
> ret = NULL;
> goto out;
> }
> @@ -710,9 +739,9 @@ EXPORT_SYMBOL_GPL(pci_alloc_p2pmem);
> void pci_free_p2pmem(struct pci_dev *pdev, void *addr, size_t size)
> {
> struct percpu_ref *ref;
> + struct pci_p2pdma *p2pdma = rcu_dereference_protected(pdev->p2pdma, 1);
>
> - gen_pool_free_owner(pdev->p2pdma->pool, (uintptr_t)addr, size,
> - (void **) &ref);
> + gen_pool_free_owner(p2pdma->pool, (uintptr_t)addr, size, (void **) &ref);
> percpu_ref_put(ref);
> }
> EXPORT_SYMBOL_GPL(pci_free_p2pmem);
> @@ -725,9 +754,12 @@ EXPORT_SYMBOL_GPL(pci_free_p2pmem);
> */
> pci_bus_addr_t pci_p2pmem_virt_to_bus(struct pci_dev *pdev, void *addr)
> {
> + struct pci_p2pdma *p2pdma;
> +
> if (!addr)
> return 0;
> - if (!pdev->p2pdma)
> + p2pdma = rcu_dereference_protected(pdev->p2pdma, 1);
> + if (!p2pdma)
> return 0;
>
> /*
> @@ -735,7 +767,7 @@ pci_bus_addr_t pci_p2pmem_virt_to_bus(struct pci_dev *pdev, void *addr)
> * bus address as the physical address. So gen_pool_virt_to_phys()
> * actually returns the bus address despite the misleading name.
> */
> - return gen_pool_virt_to_phys(pdev->p2pdma->pool, (unsigned long)addr);
> + return gen_pool_virt_to_phys(p2pdma->pool, (unsigned long)addr);
> }
> EXPORT_SYMBOL_GPL(pci_p2pmem_virt_to_bus);
>
> @@ -806,19 +838,30 @@ EXPORT_SYMBOL_GPL(pci_p2pmem_free_sgl);
> */
> void pci_p2pmem_publish(struct pci_dev *pdev, bool publish)
> {
> - if (pdev->p2pdma)
> - pdev->p2pdma->p2pmem_published = publish;
> + struct pci_p2pdma *p2pdma;
> +
> + rcu_read_lock();
> + p2pdma = rcu_dereference(pdev->p2pdma);
> + if (p2pdma)
> + p2pdma->p2pmem_published = publish;
> + rcu_read_unlock();
> }
> EXPORT_SYMBOL_GPL(pci_p2pmem_publish);
>
> static enum pci_p2pdma_map_type pci_p2pdma_map_type(struct pci_dev *provider,
> struct pci_dev *client)
> {
> - if (!provider->p2pdma)
> - return PCI_P2PDMA_MAP_NOT_SUPPORTED;
> + enum pci_p2pdma_map_type type = PCI_P2PDMA_MAP_NOT_SUPPORTED;
> + struct pci_p2pdma *p2pdma;
>
> - return xa_to_value(xa_load(&provider->p2pdma->map_types,
> - map_types_idx(client)));
> + rcu_read_lock();
> + p2pdma = rcu_dereference(provider->p2pdma);
> +
> + if (p2pdma)
> + type = xa_to_value(xa_load(&p2pdma->map_types,
> + map_types_idx(client)));
> + rcu_read_unlock();
> + return type;
> }
>
> static int __pci_p2pdma_map_sg(struct pci_p2pdma_pagemap *p2p_pgmap,
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 24306504226ab665be7323549d0759da1b7ac715..6abdebe2aeb1676da08f03e05e5ecb26f0b08cd6 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -497,7 +497,7 @@ struct pci_dev {
> u16 pasid_features;
> #endif
> #ifdef CONFIG_PCI_P2PDMA
> - struct pci_p2pdma *p2pdma;
> + struct pci_p2pdma __rcu *p2pdma;
> #endif
> u16 acs_cap; /* ACS Capability offset */
> phys_addr_t rom; /* Physical address if not from BAR */
> --
> 2.32.0.93.g670b81a890-goog
>

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