From: Dan Williams <dan.j.williams@xxxxxxxxx> Subject: PCI/P2PDMA: track pgmap references per resource, not globally In preparation for fixing a race between devm_memremap_pages_release() and the final put of a page from the device-page-map, allocate a percpu-ref per p2pdma resource mapping. Link: http://lkml.kernel.org/r/155727338646.292046.9922678317501435597.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx> Reviewed-by: Ira Weiny <ira.weiny@xxxxxxxxx> Reviewed-by: Logan Gunthorpe <logang@xxxxxxxxxxxx> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxx> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Cc: "Jérôme Glisse" <jglisse@xxxxxxxxxx> Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- drivers/pci/p2pdma.c | 124 ++++++++++++++++++++++++++--------------- 1 file changed, 81 insertions(+), 43 deletions(-) --- a/drivers/pci/p2pdma.c~pci-p2pdma-track-pgmap-references-per-resource-not-globally +++ a/drivers/pci/p2pdma.c @@ -20,12 +20,16 @@ #include <linux/seq_buf.h> struct pci_p2pdma { - struct percpu_ref devmap_ref; - struct completion devmap_ref_done; struct gen_pool *pool; bool p2pmem_published; }; +struct p2pdma_pagemap { + struct dev_pagemap pgmap; + struct percpu_ref ref; + struct completion ref_done; +}; + static ssize_t size_show(struct device *dev, struct device_attribute *attr, char *buf) { @@ -74,41 +78,45 @@ static const struct attribute_group p2pm .name = "p2pmem", }; +static struct p2pdma_pagemap *to_p2p_pgmap(struct percpu_ref *ref) +{ + return container_of(ref, struct p2pdma_pagemap, ref); +} + static void pci_p2pdma_percpu_release(struct percpu_ref *ref) { - struct pci_p2pdma *p2p = - container_of(ref, struct pci_p2pdma, devmap_ref); + struct p2pdma_pagemap *p2p_pgmap = to_p2p_pgmap(ref); - complete_all(&p2p->devmap_ref_done); + complete(&p2p_pgmap->ref_done); } static void pci_p2pdma_percpu_kill(struct percpu_ref *ref) { - /* - * pci_p2pdma_add_resource() may be called multiple times - * by a driver and may register the percpu_kill devm action multiple - * times. We only want the first action to actually kill the - * percpu_ref. - */ - if (percpu_ref_is_dying(ref)) - return; - percpu_ref_kill(ref); } +static void pci_p2pdma_percpu_cleanup(void *ref) +{ + struct p2pdma_pagemap *p2p_pgmap = to_p2p_pgmap(ref); + + wait_for_completion(&p2p_pgmap->ref_done); + percpu_ref_exit(&p2p_pgmap->ref); +} + static void pci_p2pdma_release(void *data) { struct pci_dev *pdev = data; + struct pci_p2pdma *p2pdma = pdev->p2pdma; - if (!pdev->p2pdma) + if (!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); + gen_pool_destroy(p2pdma->pool); sysfs_remove_group(&pdev->dev.kobj, &p2pmem_group); - pdev->p2pdma = NULL; } static int pci_p2pdma_setup(struct pci_dev *pdev) @@ -124,12 +132,6 @@ static int pci_p2pdma_setup(struct pci_d if (!p2p->pool) goto out; - init_completion(&p2p->devmap_ref_done); - error = percpu_ref_init(&p2p->devmap_ref, - pci_p2pdma_percpu_release, 0, GFP_KERNEL); - if (error) - goto out_pool_destroy; - error = devm_add_action_or_reset(&pdev->dev, pci_p2pdma_release, pdev); if (error) goto out_pool_destroy; @@ -163,6 +165,7 @@ out: int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar, size_t size, u64 offset) { + struct p2pdma_pagemap *p2p_pgmap; struct dev_pagemap *pgmap; void *addr; int error; @@ -185,14 +188,32 @@ int pci_p2pdma_add_resource(struct pci_d return error; } - pgmap = devm_kzalloc(&pdev->dev, sizeof(*pgmap), GFP_KERNEL); - if (!pgmap) + p2p_pgmap = devm_kzalloc(&pdev->dev, sizeof(*p2p_pgmap), GFP_KERNEL); + if (!p2p_pgmap) return -ENOMEM; + init_completion(&p2p_pgmap->ref_done); + error = percpu_ref_init(&p2p_pgmap->ref, + pci_p2pdma_percpu_release, 0, GFP_KERNEL); + if (error) + goto pgmap_free; + + /* + * FIXME: the percpu_ref_exit needs to be coordinated internal + * to devm_memremap_pages_release(). Duplicate the same ordering + * as other devm_memremap_pages() users for now. + */ + error = devm_add_action(&pdev->dev, pci_p2pdma_percpu_cleanup, + &p2p_pgmap->ref); + if (error) + goto ref_cleanup; + + pgmap = &p2p_pgmap->pgmap; + pgmap->res.start = pci_resource_start(pdev, bar) + offset; pgmap->res.end = pgmap->res.start + size - 1; pgmap->res.flags = pci_resource_flags(pdev, bar); - pgmap->ref = &pdev->p2pdma->devmap_ref; + pgmap->ref = &p2p_pgmap->ref; pgmap->type = MEMORY_DEVICE_PCI_P2PDMA; pgmap->pci_p2pdma_bus_offset = pci_bus_address(pdev, bar) - pci_resource_start(pdev, bar); @@ -201,12 +222,13 @@ int pci_p2pdma_add_resource(struct pci_d addr = devm_memremap_pages(&pdev->dev, pgmap); if (IS_ERR(addr)) { error = PTR_ERR(addr); - goto pgmap_free; + goto ref_exit; } - error = gen_pool_add_virt(pdev->p2pdma->pool, (unsigned long)addr, + error = gen_pool_add_owner(pdev->p2pdma->pool, (unsigned long)addr, pci_bus_address(pdev, bar) + offset, - resource_size(&pgmap->res), dev_to_node(&pdev->dev)); + resource_size(&pgmap->res), dev_to_node(&pdev->dev), + &p2p_pgmap->ref); if (error) goto pages_free; @@ -217,8 +239,10 @@ int pci_p2pdma_add_resource(struct pci_d pages_free: devm_memunmap_pages(&pdev->dev, pgmap); +ref_cleanup: + percpu_ref_exit(&p2p_pgmap->ref); pgmap_free: - devm_kfree(&pdev->dev, pgmap); + devm_kfree(&pdev->dev, p2p_pgmap); return error; } EXPORT_SYMBOL_GPL(pci_p2pdma_add_resource); @@ -587,19 +611,30 @@ EXPORT_SYMBOL_GPL(pci_p2pmem_find_many); */ void *pci_alloc_p2pmem(struct pci_dev *pdev, size_t size) { - void *ret; + void *ret = NULL; + struct percpu_ref *ref; + /* + * Pairs with synchronize_rcu() in pci_p2pdma_release() to + * ensure pdev->p2pdma is non-NULL for the duration of the + * read-lock. + */ + rcu_read_lock(); if (unlikely(!pdev->p2pdma)) - return NULL; - - if (unlikely(!percpu_ref_tryget_live(&pdev->p2pdma->devmap_ref))) - return NULL; - - ret = (void *)gen_pool_alloc(pdev->p2pdma->pool, size); + goto out; - if (unlikely(!ret)) - percpu_ref_put(&pdev->p2pdma->devmap_ref); + ret = (void *)gen_pool_alloc_owner(pdev->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); + ret = NULL; + goto out; + } +out: + rcu_read_unlock(); return ret; } EXPORT_SYMBOL_GPL(pci_alloc_p2pmem); @@ -612,8 +647,11 @@ EXPORT_SYMBOL_GPL(pci_alloc_p2pmem); */ void pci_free_p2pmem(struct pci_dev *pdev, void *addr, size_t size) { - gen_pool_free(pdev->p2pdma->pool, (uintptr_t)addr, size); - percpu_ref_put(&pdev->p2pdma->devmap_ref); + struct percpu_ref *ref; + + gen_pool_free_owner(pdev->p2pdma->pool, (uintptr_t)addr, size, + (void **) &ref); + percpu_ref_put(ref); } EXPORT_SYMBOL_GPL(pci_free_p2pmem); _
