PCI: switchtec: Fix stdev_release() crash after surprise hot remove

A PCI device hot removal may occur while stdev->cdev is held open. The call
to stdev_release() then happens during close or exit, at a point way past
switchtec_pci_remove(). Otherwise the last ref would vanish with the
trailing put_device(), just before return.

At that later point in time, the devm cleanup has already removed the
stdev->mmio_mrpc mapping. Also, the stdev->pdev reference was not a counted
one. Therefore, in DMA mode, the iowrite32() in stdev_release() will cause
a fatal page fault, and the subsequent dma_free_coherent(), if reached,
would pass a stale &stdev->pdev->dev pointer.

Fix by moving MRPC DMA shutdown into switchtec_pci_remove(), after
stdev_kill(). Counting the stdev->pdev ref is now optional, but may prevent
future accidents.

Reproducible via the script at
https://lore.kernel.org/r/20231113212150.96410-1-dns@arista.com

Link: https://lore.kernel.org/r/20231122042316.91208-2-dns@arista.com
Signed-off-by: Daniel Stodden <dns@arista.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Dmitry Safonov <dima@arista.com>

diff --git a/drivers/pci/switch/switchtec.c b/drivers/pci/switch/switchtec.c
index 5b921387eca61a7444f20ec3ae9b531c01fdb6c4..1804794d0e686f22febe508c58aa340f03eecd23 100644 (file)
--- a/drivers/pci/switch/switchtec.c
+++ b/drivers/pci/switch/switchtec.c
@@ -1308,13 +1308,6 @@ static void stdev_release(struct device *dev)
 {
        struct switchtec_dev *stdev = to_stdev(dev);
 
-       if (stdev->dma_mrpc) {
-               iowrite32(0, &stdev->mmio_mrpc->dma_en);
-               flush_wc_buf(stdev);
-               writeq(0, &stdev->mmio_mrpc->dma_addr);
-               dma_free_coherent(&stdev->pdev->dev, sizeof(*stdev->dma_mrpc),
-                               stdev->dma_mrpc, stdev->dma_mrpc_dma_addr);
-       }
        kfree(stdev);
 }
 
@@ -1358,7 +1351,7 @@ static struct switchtec_dev *stdev_create(struct pci_dev *pdev)
                return ERR_PTR(-ENOMEM);
 
        stdev->alive = true;
-       stdev->pdev = pdev;
+       stdev->pdev = pci_dev_get(pdev);
        INIT_LIST_HEAD(&stdev->mrpc_queue);
        mutex_init(&stdev->mrpc_mutex);
        stdev->mrpc_busy = 0;
@@ -1391,6 +1384,7 @@ static struct switchtec_dev *stdev_create(struct pci_dev *pdev)
        return stdev;
 
 err_put:
+       pci_dev_put(stdev->pdev);
        put_device(&stdev->dev);
        return ERR_PTR(rc);
 }
@@ -1644,6 +1638,18 @@ static int switchtec_init_pci(struct switchtec_dev *stdev,
        return 0;
 }
 
+static void switchtec_exit_pci(struct switchtec_dev *stdev)
+{
+       if (stdev->dma_mrpc) {
+               iowrite32(0, &stdev->mmio_mrpc->dma_en);
+               flush_wc_buf(stdev);
+               writeq(0, &stdev->mmio_mrpc->dma_addr);
+               dma_free_coherent(&stdev->pdev->dev, sizeof(*stdev->dma_mrpc),
+                                 stdev->dma_mrpc, stdev->dma_mrpc_dma_addr);
+               stdev->dma_mrpc = NULL;
+       }
+}
+
 static int switchtec_pci_probe(struct pci_dev *pdev,
                               const struct pci_device_id *id)
 {
@@ -1703,6 +1709,9 @@ static void switchtec_pci_remove(struct pci_dev *pdev)
        ida_free(&switchtec_minor_ida, MINOR(stdev->dev.devt));
        dev_info(&stdev->dev, "unregistered.\n");
        stdev_kill(stdev);
+       switchtec_exit_pci(stdev);
+       pci_dev_put(stdev->pdev);
+       stdev->pdev = NULL;
        put_device(&stdev->dev);
 }