Re: [PATCH 6/6] mm/devm_memremap_pages: Fix final page put race

From: Ira Weiny
Date: Fri Mar 29 2019 - 13:47:42 EST

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On Fri, Mar 29, 2019 at 08:27:55AM -0700, Dan Williams wrote:
> Logan noticed that devm_memremap_pages_release() kills the percpu_ref
> drops all the page references that were acquired at init and then
> immediately proceeds to unplug, arch_remove_memory(), the backing pages
> for the pagemap. If for some reason device shutdown actually collides
> with a busy / elevated-ref-count page then arch_remove_memory() should
> be deferred until after that reference is dropped.
>
> As it stands the "wait for last page ref drop" happens *after*
> devm_memremap_pages_release() returns, which is obviously too late and
> can lead to crashes.
>
> Fix this situation by assigning the responsibility to wait for the
> percpu_ref to go idle to devm_memremap_pages() with a new ->cleanup()
> callback. Implement the new cleanup callback for all
> devm_memremap_pages() users: pmem, devdax, hmm, and p2pdma.
>
> Reported-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
> Fixes: 41e94a851304 ("add devm_memremap_pages")
> Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> Cc: "Jérôme Glisse" <jglisse@xxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>

For the series:

Reviewed-by: Ira Weiny <ira.weiny@xxxxxxxxx>

> ---
> drivers/dax/device.c | 13 +++----------
> drivers/nvdimm/pmem.c | 17 +++++++++++++----
> drivers/pci/p2pdma.c | 17 +++--------------
> include/linux/memremap.h | 2 ++
> kernel/memremap.c | 17 ++++++++++++-----
> mm/hmm.c | 14 +++-----------
> tools/testing/nvdimm/test/iomap.c | 2 ++
> 7 files changed, 38 insertions(+), 44 deletions(-)
>
> diff --git a/drivers/dax/device.c b/drivers/dax/device.c
> index e428468ab661..e3aa78dd1bb0 100644
> --- a/drivers/dax/device.c
> +++ b/drivers/dax/device.c
> @@ -27,9 +27,8 @@ static void dev_dax_percpu_release(struct percpu_ref *ref)
> complete(&dev_dax->cmp);
> }
>
> -static void dev_dax_percpu_exit(void *data)
> +static void dev_dax_percpu_exit(struct percpu_ref *ref)
> {
> - struct percpu_ref *ref = data;
> struct dev_dax *dev_dax = ref_to_dev_dax(ref);
>
> dev_dbg(&dev_dax->dev, "%s\n", __func__);
> @@ -468,18 +467,12 @@ int dev_dax_probe(struct device *dev)
> if (rc)
> return rc;
>
> - rc = devm_add_action_or_reset(dev, dev_dax_percpu_exit, &dev_dax->ref);
> - if (rc)
> - return rc;
> -
> dev_dax->pgmap.ref = &dev_dax->ref;
> dev_dax->pgmap.kill = dev_dax_percpu_kill;
> + dev_dax->pgmap.cleanup = dev_dax_percpu_exit;
> addr = devm_memremap_pages(dev, &dev_dax->pgmap);
> - if (IS_ERR(addr)) {
> - devm_remove_action(dev, dev_dax_percpu_exit, &dev_dax->ref);
> - percpu_ref_exit(&dev_dax->ref);
> + if (IS_ERR(addr))
> return PTR_ERR(addr);
> - }
>
> inode = dax_inode(dax_dev);
> cdev = inode->i_cdev;
> diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
> index bc2f700feef8..507b9eda42aa 100644
> --- a/drivers/nvdimm/pmem.c
> +++ b/drivers/nvdimm/pmem.c
> @@ -304,11 +304,19 @@ static const struct attribute_group *pmem_attribute_groups[] = {
> NULL,
> };
>
> -static void pmem_release_queue(void *q)
> +static void __pmem_release_queue(struct percpu_ref *ref)
> {
> + struct request_queue *q;
> +
> + q = container_of(ref, typeof(*q), q_usage_counter);
> blk_cleanup_queue(q);
> }
>
> +static void pmem_release_queue(void *ref)
> +{
> + __pmem_release_queue(ref);
> +}
> +
> static void pmem_freeze_queue(struct percpu_ref *ref)
> {
> struct request_queue *q;
> @@ -400,12 +408,10 @@ static int pmem_attach_disk(struct device *dev,
> if (!q)
> return -ENOMEM;
>
> - if (devm_add_action_or_reset(dev, pmem_release_queue, q))
> - return -ENOMEM;
> -
> pmem->pfn_flags = PFN_DEV;
> pmem->pgmap.ref = &q->q_usage_counter;
> pmem->pgmap.kill = pmem_freeze_queue;
> + pmem->pgmap.cleanup = __pmem_release_queue;
> if (is_nd_pfn(dev)) {
> if (setup_pagemap_fsdax(dev, &pmem->pgmap))
> return -ENOMEM;
> @@ -426,6 +432,9 @@ static int pmem_attach_disk(struct device *dev,
> pmem->pfn_flags |= PFN_MAP;
> memcpy(&bb_res, &pmem->pgmap.res, sizeof(bb_res));
> } else {
> + if (devm_add_action_or_reset(dev, pmem_release_queue,
> + &q->q_usage_counter))
> + return -ENOMEM;
> addr = devm_memremap(dev, pmem->phys_addr,
> pmem->size, ARCH_MEMREMAP_PMEM);
> memcpy(&bb_res, &nsio->res, sizeof(bb_res));
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index 1b96c1688715..7ff5b8067670 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -95,7 +95,7 @@ static void pci_p2pdma_percpu_kill(struct percpu_ref *ref)
> percpu_ref_kill(ref);
> }
>
> -static void pci_p2pdma_percpu_cleanup(void *ref)
> +static void pci_p2pdma_percpu_cleanup(struct percpu_ref *ref)
> {
> struct p2pdma_pagemap *p2p_pgmap = to_p2p_pgmap(ref);
>
> @@ -197,16 +197,6 @@ int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar, size_t size,
> 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;
> @@ -217,11 +207,12 @@ int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar, size_t size,
> pgmap->pci_p2pdma_bus_offset = pci_bus_address(pdev, bar) -
> pci_resource_start(pdev, bar);
> pgmap->kill = pci_p2pdma_percpu_kill;
> + pgmap->cleanup = pci_p2pdma_percpu_cleanup;
>
> addr = devm_memremap_pages(&pdev->dev, pgmap);
> if (IS_ERR(addr)) {
> error = PTR_ERR(addr);
> - goto ref_exit;
> + goto pgmap_free;
> }
>
> error = gen_pool_add_owner(pdev->p2pdma->pool, (unsigned long)addr,
> @@ -238,8 +229,6 @@ int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar, size_t size,
>
> pages_free:
> devm_memunmap_pages(&pdev->dev, pgmap);
> -ref_cleanup:
> - percpu_ref_exit(&p2p_pgmap->ref);
> pgmap_free:
> devm_kfree(&pdev->dev, p2p_pgmap);
> return error;
> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
> index 7601ee314c4a..1732dea030b2 100644
> --- a/include/linux/memremap.h
> +++ b/include/linux/memremap.h
> @@ -81,6 +81,7 @@ typedef void (*dev_page_free_t)(struct page *page, void *data);
> * @res: physical address range covered by @ref
> * @ref: reference count that pins the devm_memremap_pages() mapping
> * @kill: callback to transition @ref to the dead state
> + * @cleanup: callback to wait for @ref to be idle and reap it
> * @dev: host device of the mapping for debug
> * @data: private data pointer for page_free()
> * @type: memory type: see MEMORY_* in memory_hotplug.h
> @@ -92,6 +93,7 @@ struct dev_pagemap {
> struct resource res;
> struct percpu_ref *ref;
> void (*kill)(struct percpu_ref *ref);
> + void (*cleanup)(struct percpu_ref *ref);
> struct device *dev;
> void *data;
> enum memory_type type;
> diff --git a/kernel/memremap.c b/kernel/memremap.c
> index 65afbacab44e..05d1af5a2f15 100644
> --- a/kernel/memremap.c
> +++ b/kernel/memremap.c
> @@ -96,6 +96,7 @@ static void devm_memremap_pages_release(void *data)
> pgmap->kill(pgmap->ref);
> for_each_device_pfn(pfn, pgmap)
> put_page(pfn_to_page(pfn));
> + pgmap->cleanup(pgmap->ref);
>
> /* pages are dead and unused, undo the arch mapping */
> align_start = res->start & ~(SECTION_SIZE - 1);
> @@ -134,8 +135,8 @@ static void devm_memremap_pages_release(void *data)
> * 2/ The altmap field may optionally be initialized, in which case altmap_valid
> * must be set to true
> *
> - * 3/ pgmap->ref must be 'live' on entry and will be killed at
> - * devm_memremap_pages_release() time, or if this routine fails.
> + * 3/ pgmap->ref must be 'live' on entry and will be killed and reaped
> + * at devm_memremap_pages_release() time, or if this routine fails.
> *
> * 4/ res is expected to be a host memory range that could feasibly be
> * treated as a "System RAM" range, i.e. not a device mmio range, but
> @@ -151,8 +152,10 @@ void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap)
> pgprot_t pgprot = PAGE_KERNEL;
> int error, nid, is_ram;
>
> - if (!pgmap->ref || !pgmap->kill)
> + if (!pgmap->ref || !pgmap->kill || !pgmap->cleanup) {
> + WARN(1, "Missing reference count teardown definition\n");
> return ERR_PTR(-EINVAL);
> + }
>
> align_start = res->start & ~(SECTION_SIZE - 1);
> align_size = ALIGN(res->start + resource_size(res), SECTION_SIZE)
> @@ -163,14 +166,16 @@ void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap)
> if (conflict_pgmap) {
> dev_WARN(dev, "Conflicting mapping in same section\n");
> put_dev_pagemap(conflict_pgmap);
> - return ERR_PTR(-ENOMEM);
> + error = -ENOMEM;
> + goto err_array;
> }
>
> conflict_pgmap = get_dev_pagemap(PHYS_PFN(align_end), NULL);
> if (conflict_pgmap) {
> dev_WARN(dev, "Conflicting mapping in same section\n");
> put_dev_pagemap(conflict_pgmap);
> - return ERR_PTR(-ENOMEM);
> + error = -ENOMEM;
> + goto err_array;
> }
>
> is_ram = region_intersects(align_start, align_size,
> @@ -262,6 +267,8 @@ void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap)
> pgmap_array_delete(res);
> err_array:
> pgmap->kill(pgmap->ref);
> + pgmap->cleanup(pgmap->ref);
> +
> return ERR_PTR(error);
> }
> EXPORT_SYMBOL_GPL(devm_memremap_pages);
> diff --git a/mm/hmm.c b/mm/hmm.c
> index fe1cd87e49ac..225ade644058 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -975,9 +975,8 @@ static void hmm_devmem_ref_release(struct percpu_ref *ref)
> complete(&devmem->completion);
> }
>
> -static void hmm_devmem_ref_exit(void *data)
> +static void hmm_devmem_ref_exit(struct percpu_ref *ref)
> {
> - struct percpu_ref *ref = data;
> struct hmm_devmem *devmem;
>
> devmem = container_of(ref, struct hmm_devmem, ref);
> @@ -1054,10 +1053,6 @@ struct hmm_devmem *hmm_devmem_add(const struct hmm_devmem_ops *ops,
> if (ret)
> return ERR_PTR(ret);
>
> - ret = devm_add_action_or_reset(device, hmm_devmem_ref_exit, &devmem->ref);
> - if (ret)
> - return ERR_PTR(ret);
> -
> size = ALIGN(size, PA_SECTION_SIZE);
> addr = min((unsigned long)iomem_resource.end,
> (1UL << MAX_PHYSMEM_BITS) - 1);
> @@ -1096,6 +1091,7 @@ struct hmm_devmem *hmm_devmem_add(const struct hmm_devmem_ops *ops,
> devmem->pagemap.ref = &devmem->ref;
> devmem->pagemap.data = devmem;
> devmem->pagemap.kill = hmm_devmem_ref_kill;
> + devmem->pagemap.cleanup = hmm_devmem_ref_exit;
>
> result = devm_memremap_pages(devmem->device, &devmem->pagemap);
> if (IS_ERR(result))
> @@ -1133,11 +1129,6 @@ struct hmm_devmem *hmm_devmem_add_resource(const struct hmm_devmem_ops *ops,
> if (ret)
> return ERR_PTR(ret);
>
> - ret = devm_add_action_or_reset(device, hmm_devmem_ref_exit,
> - &devmem->ref);
> - if (ret)
> - return ERR_PTR(ret);
> -
> devmem->pfn_first = devmem->resource->start >> PAGE_SHIFT;
> devmem->pfn_last = devmem->pfn_first +
> (resource_size(devmem->resource) >> PAGE_SHIFT);
> @@ -1150,6 +1141,7 @@ struct hmm_devmem *hmm_devmem_add_resource(const struct hmm_devmem_ops *ops,
> devmem->pagemap.ref = &devmem->ref;
> devmem->pagemap.data = devmem;
> devmem->pagemap.kill = hmm_devmem_ref_kill;
> + devmem->pagemap.cleanup = hmm_devmem_ref_exit;
>
> result = devm_memremap_pages(devmem->device, &devmem->pagemap);
> if (IS_ERR(result))
> diff --git a/tools/testing/nvdimm/test/iomap.c b/tools/testing/nvdimm/test/iomap.c
> index c6635fee27d8..219dd0a1cb08 100644
> --- a/tools/testing/nvdimm/test/iomap.c
> +++ b/tools/testing/nvdimm/test/iomap.c
> @@ -108,7 +108,9 @@ static void nfit_test_kill(void *_pgmap)
> {
> struct dev_pagemap *pgmap = _pgmap;
>
> + WARN_ON(!pgmap || !pgmap->ref || !pgmap->kill || !pgmap->cleanup);
> pgmap->kill(pgmap->ref);
> + pgmap->cleanup(pgmap->ref);
> }
>
> void *__wrap_devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap)
>

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In reply to: Dan Williams: "[PATCH 6/6] mm/devm_memremap_pages: Fix final page put race"
Next in thread: Dan Williams: "[PATCH 5/6] pci/p2pdma: Track pgmap references per resource, not globally"
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