Re: [PATCH 11/25] memremap: lift the devmap_enable manipulation into devm_memremap_pages

[Ira Weiny]

On Wed, Jun 26, 2019 at 02:27:10PM +0200, Christoph Hellwig wrote:
> Just check if there is a ->page_free operation set and take care of the
> static key enable, as well as the put using device managed resources.
> Also check that a ->page_free is provided for the pgmaps types that
> require it, and check for a valid type as well while we are at it.
> 
> Note that this also fixes the fact that hmm never called
> dev_pagemap_put_ops and thus would leave the slow path enabled forever,
> even after a device driver unload or disable.
> 
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
>  drivers/nvdimm/pmem.c | 23 +++--------------
>  include/linux/mm.h    | 10 --------
>  kernel/memremap.c     | 59 +++++++++++++++++++++++++++----------------
>  mm/hmm.c              |  2 --
>  4 files changed, 41 insertions(+), 53 deletions(-)
> 
> diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
> index 9dac48359353..48767171a4df 100644
> --- a/drivers/nvdimm/pmem.c
> +++ b/drivers/nvdimm/pmem.c
> @@ -334,11 +334,6 @@ static void pmem_release_disk(void *__pmem)
>  	put_disk(pmem->disk);
>  }
>  
> -static void pmem_release_pgmap_ops(void *__pgmap)
> -{
> -	dev_pagemap_put_ops();
> -}
> -
>  static void pmem_pagemap_page_free(struct page *page, void *data)
>  {
>  	wake_up_var(&page->_refcount);
> @@ -350,16 +345,6 @@ static const struct dev_pagemap_ops fsdax_pagemap_ops = {
>  	.cleanup		= pmem_pagemap_cleanup,
>  };
>  
> -static int setup_pagemap_fsdax(struct device *dev, struct dev_pagemap *pgmap)
> -{
> -	dev_pagemap_get_ops();
> -	if (devm_add_action_or_reset(dev, pmem_release_pgmap_ops, pgmap))
> -		return -ENOMEM;
> -	pgmap->type = MEMORY_DEVICE_FS_DAX;
> -	pgmap->ops = &fsdax_pagemap_ops;
> -	return 0;
> -}
> -
>  static int pmem_attach_disk(struct device *dev,
>  		struct nd_namespace_common *ndns)
>  {
> @@ -415,8 +400,8 @@ static int pmem_attach_disk(struct device *dev,
>  	pmem->pfn_flags = PFN_DEV;
>  	pmem->pgmap.ref = &q->q_usage_counter;
>  	if (is_nd_pfn(dev)) {
> -		if (setup_pagemap_fsdax(dev, &pmem->pgmap))
> -			return -ENOMEM;
> +		pmem->pgmap.type = MEMORY_DEVICE_FS_DAX;
> +		pmem->pgmap.ops = &fsdax_pagemap_ops;
>  		addr = devm_memremap_pages(dev, &pmem->pgmap);
>  		pfn_sb = nd_pfn->pfn_sb;
>  		pmem->data_offset = le64_to_cpu(pfn_sb->dataoff);
> @@ -428,8 +413,8 @@ static int pmem_attach_disk(struct device *dev,
>  	} else if (pmem_should_map_pages(dev)) {
>  		memcpy(&pmem->pgmap.res, &nsio->res, sizeof(pmem->pgmap.res));
>  		pmem->pgmap.altmap_valid = false;
> -		if (setup_pagemap_fsdax(dev, &pmem->pgmap))
> -			return -ENOMEM;
> +		pmem->pgmap.type = MEMORY_DEVICE_FS_DAX;
> +		pmem->pgmap.ops = &fsdax_pagemap_ops;
>  		addr = devm_memremap_pages(dev, &pmem->pgmap);
>  		pmem->pfn_flags |= PFN_MAP;
>  		memcpy(&bb_res, &pmem->pgmap.res, sizeof(bb_res));
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 6e4b9be08b13..aa3970291cdf 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -932,8 +932,6 @@ static inline bool is_zone_device_page(const struct page *page)
>  #endif
>  
>  #ifdef CONFIG_DEV_PAGEMAP_OPS
> -void dev_pagemap_get_ops(void);
> -void dev_pagemap_put_ops(void);
>  void __put_devmap_managed_page(struct page *page);
>  DECLARE_STATIC_KEY_FALSE(devmap_managed_key);
>  static inline bool put_devmap_managed_page(struct page *page)
> @@ -973,14 +971,6 @@ static inline bool is_pci_p2pdma_page(const struct page *page)
>  #endif /* CONFIG_PCI_P2PDMA */
>  
>  #else /* CONFIG_DEV_PAGEMAP_OPS */
> -static inline void dev_pagemap_get_ops(void)
> -{
> -}
> -
> -static inline void dev_pagemap_put_ops(void)
> -{
> -}
> -
>  static inline bool put_devmap_managed_page(struct page *page)
>  {
>  	return false;
> diff --git a/kernel/memremap.c b/kernel/memremap.c
> index 00c1ceb60c19..3219a4c91d07 100644
> --- a/kernel/memremap.c
> +++ b/kernel/memremap.c
> @@ -17,6 +17,35 @@ static DEFINE_XARRAY(pgmap_array);
>  #define SECTION_MASK ~((1UL << PA_SECTION_SHIFT) - 1)
>  #define SECTION_SIZE (1UL << PA_SECTION_SHIFT)
>  
> +#ifdef CONFIG_DEV_PAGEMAP_OPS
> +DEFINE_STATIC_KEY_FALSE(devmap_managed_key);
> +EXPORT_SYMBOL(devmap_managed_key);
> +static atomic_t devmap_managed_enable;
> +
> +static void devmap_managed_enable_put(void *data)
> +{
> +	if (atomic_dec_and_test(&devmap_managed_enable))
> +		static_branch_disable(&devmap_managed_key);
> +}
> +
> +static int devmap_managed_enable_get(struct device *dev, struct dev_pagemap *pgmap)
> +{
> +	if (!pgmap->ops->page_free) {

NIT: later on you add the check for pgmap->ops...  it should probably be here.

But not sure that bisection will be an issue here.

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

> +		WARN(1, "Missing page_free method\n");
> +		return -EINVAL;
> +	}
> +
> +	if (atomic_inc_return(&devmap_managed_enable) == 1)
> +		static_branch_enable(&devmap_managed_key);
> +	return devm_add_action_or_reset(dev, devmap_managed_enable_put, NULL);
> +}
> +#else
> +static int devmap_managed_enable_get(struct device *dev, struct dev_pagemap *pgmap)
> +{
> +	return -EINVAL;
> +}
> +#endif /* CONFIG_DEV_PAGEMAP_OPS */
> +
>  #if IS_ENABLED(CONFIG_DEVICE_PRIVATE)
>  vm_fault_t device_private_entry_fault(struct vm_area_struct *vma,
>  		       unsigned long addr,
> @@ -156,6 +185,7 @@ void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap)
>  	};
>  	pgprot_t pgprot = PAGE_KERNEL;
>  	int error, nid, is_ram;
> +	bool need_devmap_managed = true;
>  
>  	switch (pgmap->type) {
>  	case MEMORY_DEVICE_PRIVATE:
> @@ -173,6 +203,7 @@ void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap)
>  		break;
>  	case MEMORY_DEVICE_DEVDAX:
>  	case MEMORY_DEVICE_PCI_P2PDMA:
> +		need_devmap_managed = false;
>  		break;
>  	default:
>  		WARN(1, "Invalid pgmap type %d\n", pgmap->type);
> @@ -185,6 +216,12 @@ void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap)
>  		return ERR_PTR(-EINVAL);
>  	}
>  
> +	if (need_devmap_managed) {
> +		error = devmap_managed_enable_get(dev, pgmap);
> +		if (error)
> +			return ERR_PTR(error);
> +	}
> +
>  	align_start = res->start & ~(SECTION_SIZE - 1);
>  	align_size = ALIGN(res->start + resource_size(res), SECTION_SIZE)
>  		- align_start;
> @@ -351,28 +388,6 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
>  EXPORT_SYMBOL_GPL(get_dev_pagemap);
>  
>  #ifdef CONFIG_DEV_PAGEMAP_OPS
> -DEFINE_STATIC_KEY_FALSE(devmap_managed_key);
> -EXPORT_SYMBOL(devmap_managed_key);
> -static atomic_t devmap_enable;
> -
> -/*
> - * Toggle the static key for ->page_free() callbacks when dev_pagemap
> - * pages go idle.
> - */
> -void dev_pagemap_get_ops(void)
> -{
> -	if (atomic_inc_return(&devmap_enable) == 1)
> -		static_branch_enable(&devmap_managed_key);
> -}
> -EXPORT_SYMBOL_GPL(dev_pagemap_get_ops);
> -
> -void dev_pagemap_put_ops(void)
> -{
> -	if (atomic_dec_and_test(&devmap_enable))
> -		static_branch_disable(&devmap_managed_key);
> -}
> -EXPORT_SYMBOL_GPL(dev_pagemap_put_ops);
> -
>  void __put_devmap_managed_page(struct page *page)
>  {
>  	int count = page_ref_dec_return(page);
> diff --git a/mm/hmm.c b/mm/hmm.c
> index 987793fba923..5b0bd5f6a74f 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -1415,8 +1415,6 @@ struct hmm_devmem *hmm_devmem_add(const struct hmm_devmem_ops *ops,
>  	void *result;
>  	int ret;
>  
> -	dev_pagemap_get_ops();
> -
>  	devmem = devm_kzalloc(device, sizeof(*devmem), GFP_KERNEL);
>  	if (!devmem)
>  		return ERR_PTR(-ENOMEM);
> -- 
> 2.20.1
> 
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