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@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: 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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index d5736b31ce6602f7738d74480629b305a91816fc..eecba8fbe251e611ae8385fa23a55aa2b12dff18 100644 (file)
--- a/drivers/pci/p2pdma.c
+++ b/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 p2pmem_group = {
        .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_dev *pdev)
        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_dev *pdev, int bar, size_t size,
                        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_dev *pdev, int bar, size_t size,
        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_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, 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);