PCI: Fix is_added/is_busmaster race condition

When a PCI device is detected, pdev->is_added is set to 1 and proc and
sysfs entries are created.

When the device is removed, pdev->is_added is checked for one and then
device is detached with clearing of proc and sys entries and at end,
pdev->is_added is set to 0.

is_added and is_busmaster are bit fields in pci_dev structure sharing same
memory location.

A strange issue was observed with multiple removal and rescan of a PCIe
NVMe device using sysfs commands where is_added flag was observed as zero
instead of one while removing device and proc,sys entries are not cleared.
This causes issue in later device addition with warning message
"proc_dir_entry" already registered.

Debugging revealed a race condition between the PCI core setting the
is_added bit in pci_bus_add_device() and the NVMe driver reset work-queue
setting the is_busmaster bit in pci_set_master().  As these fields are not
handled atomically, that clears the is_added bit.

Move the is_added bit to a separate private flag variable and use atomic
functions to set and retrieve the device addition state.  This avoids the
race because is_added no longer shares a memory location with is_busmaster.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=200283
Signed-off-by: Hari Vyas <hari.vyas@broadcom.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Lukas Wunner <lukas@wunner.de>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>

9 files changed, 27 insertions, 12 deletions

diff --git a/arch/powerpc/kernel/pci-common.c b/arch/powerpc/kernel/pci-common.c
index fe9733ffffaa..471aac313b89 100644
--- a/arch/powerpc/kernel/pci-common.c
+++ b/arch/powerpc/kernel/pci-common.c
@@ -42,6 +42,8 @@
 #include <asm/ppc-pci.h>
 #include <asm/eeh.h>
 
+#include "../../../drivers/pci/pci.h"
+
 /* hose_spinlock protects accesses to the the phb_bitmap. */
 static DEFINE_SPINLOCK(hose_spinlock);
 LIST_HEAD(hose_list);
@@ -1014,7 +1016,7 @@ void pcibios_setup_bus_devices(struct pci_bus *bus)
                 /* Cardbus can call us to add new devices to a bus, so ignore
                  * those who are already fully discovered
                  */
-                if (dev->is_added)
+                if (pci_dev_is_added(dev))
                         continue;
 
                 pcibios_setup_device(dev);
diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
index 5bd0eb6681bc..70b2e1e0f23c 100644
--- a/arch/powerpc/platforms/powernv/pci-ioda.c
+++ b/arch/powerpc/platforms/powernv/pci-ioda.c
@@ -46,6 +46,7 @@
 
 #include "powernv.h"
 #include "pci.h"
+#include "../../../../drivers/pci/pci.h"
 
 #define PNV_IODA1_M64_NUM       16      /* Number of M64 BARs   */
 #define PNV_IODA1_M64_SEGS      8       /* Segments per M64 BAR */
@@ -3138,7 +3139,7 @@ static void pnv_pci_ioda_fixup_iov_resources(struct pci_dev *pdev)
         struct pci_dn *pdn;
         int mul, total_vfs;
 
-        if (!pdev->is_physfn || pdev->is_added)
+        if (!pdev->is_physfn || pci_dev_is_added(pdev))
                 return;
 
         pdn = pci_get_pdn(pdev);
diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c
index 139f0af6c3d9..8a4868a3964b 100644
--- a/arch/powerpc/platforms/pseries/setup.c
+++ b/arch/powerpc/platforms/pseries/setup.c
@@ -71,6 +71,7 @@
 #include <asm/security_features.h>
 
 #include "pseries.h"
+#include "../../../../drivers/pci/pci.h"
 
 int CMO_PrPSP = -1;
 int CMO_SecPSP = -1;
@@ -664,7 +665,7 @@ static void pseries_pci_fixup_iov_resources(struct pci_dev *pdev)
         const int *indexes;
         struct device_node *dn = pci_device_to_OF_node(pdev);
 
-        if (!pdev->is_physfn || pdev->is_added)
+        if (!pdev->is_physfn || pci_dev_is_added(pdev))
                 return;
         /*Firmware must support open sriov otherwise dont configure*/
         indexes = of_get_property(dn, "ibm,open-sriov-vf-bar-info", NULL);
diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
index 35b7fc87eac5..5cb40b2518f9 100644
--- a/drivers/pci/bus.c
+++ b/drivers/pci/bus.c
@@ -330,7 +330,7 @@ void pci_bus_add_device(struct pci_dev *dev)
                 return;
         }
 
-        dev->is_added = 1;
+        pci_dev_assign_added(dev, true);
 }
 EXPORT_SYMBOL_GPL(pci_bus_add_device);
 
@@ -347,14 +347,14 @@ void pci_bus_add_devices(const struct pci_bus *bus)
 
         list_for_each_entry(dev, &bus->devices, bus_list) {
                 /* Skip already-added devices */
-                if (dev->is_added)
+                if (pci_dev_is_added(dev))
                         continue;
                 pci_bus_add_device(dev);
         }
 
         list_for_each_entry(dev, &bus->devices, bus_list) {
                 /* Skip if device attach failed */
-                if (!dev->is_added)
+                if (!pci_dev_is_added(dev))
                         continue;
                 child = dev->subordinate;
                 if (child)
diff --git a/drivers/pci/hotplug/acpiphp_glue.c b/drivers/pci/hotplug/acpiphp_glue.c
index 3a17b290df5d..ef0b1b6ba86f 100644
--- a/drivers/pci/hotplug/acpiphp_glue.c
+++ b/drivers/pci/hotplug/acpiphp_glue.c
@@ -509,7 +509,7 @@ static void enable_slot(struct acpiphp_slot *slot)
 
         list_for_each_entry(dev, &bus->devices, bus_list) {
                 /* Assume that newly added devices are powered on already. */
-                if (!dev->is_added)
+                if (!pci_dev_is_added(dev))
                         dev->current_state = PCI_D0;
         }
 
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 882f1f9596df..08817253c8a2 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -288,6 +288,7 @@ struct pci_sriov {
 
 /* pci_dev priv_flags */
 #define PCI_DEV_DISCONNECTED 0
+#define PCI_DEV_ADDED 1
 
 static inline int pci_dev_set_disconnected(struct pci_dev *dev, void *unused)
 {
@@ -300,6 +301,16 @@ static inline bool pci_dev_is_disconnected(const struct pci_dev *dev)
         return test_bit(PCI_DEV_DISCONNECTED, &dev->priv_flags);
 }
 
+static inline void pci_dev_assign_added(struct pci_dev *dev, bool added)
+{
+        assign_bit(PCI_DEV_ADDED, &dev->priv_flags, added);
+}
+
+static inline bool pci_dev_is_added(const struct pci_dev *dev)
+{
+        return test_bit(PCI_DEV_ADDED, &dev->priv_flags);
+}
+
 #ifdef CONFIG_PCI_ATS
 void pci_restore_ats_state(struct pci_dev *dev);
 #else
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index ac876e32de4b..611adcd9c169 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2433,13 +2433,13 @@ int pci_scan_slot(struct pci_bus *bus, int devfn)
         dev = pci_scan_single_device(bus, devfn);
         if (!dev)
                 return 0;
-        if (!dev->is_added)
+        if (!pci_dev_is_added(dev))
                 nr++;
 
         for (fn = next_fn(bus, dev, 0); fn > 0; fn = next_fn(bus, dev, fn)) {
                 dev = pci_scan_single_device(bus, devfn + fn);
                 if (dev) {
-                        if (!dev->is_added)
+                        if (!pci_dev_is_added(dev))
                                 nr++;
                         dev->multifunction = 1;
                 }
diff --git a/drivers/pci/remove.c b/drivers/pci/remove.c
index 6f072eae4f7a..5e3d0dced2b8 100644
--- a/drivers/pci/remove.c
+++ b/drivers/pci/remove.c
@@ -19,11 +19,12 @@ static void pci_stop_dev(struct pci_dev *dev)
 {
         pci_pme_active(dev, false);
 
-        if (dev->is_added) {
+        if (pci_dev_is_added(dev)) {
                 device_release_driver(&dev->dev);
                 pci_proc_detach_device(dev);
                 pci_remove_sysfs_dev_files(dev);
-                dev->is_added = 0;
+
+                pci_dev_assign_added(dev, false);
         }
 
         if (dev->bus->self)
diff --git a/include/linux/pci.h b/include/linux/pci.h
index abd5d5e17aee..c133ccfa002e 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -368,7 +368,6 @@ struct pci_dev {
         unsigned int    transparent:1;          /* Subtractive decode bridge */
         unsigned int    multifunction:1;        /* Multi-function device */
 
-        unsigned int    is_added:1;
         unsigned int    is_busmaster:1;         /* Is busmaster */
         unsigned int    no_msi:1;               /* May not use MSI */
         unsigned int    no_64bit_msi:1;         /* May only use 32-bit MSIs */