[RFC PATCH 4/6] pci: Add a mutex to pci_dev to protect device state

[Benjamin Herrenschmidt]

This adds a pci_dev mutex which will be used to fix a number
of races related to the various state bits maintained in
that structure.

We call it "state_lock" with similarly named accessors to avoid
confusion with the pci_dev_lock() which uses the device_lock().

This is a low level mutex meant to protect the mapping between
the state fields and the hardware state, for example enabling
disabling, setting/clearing bus master etc...

These operations can happen while the device_lock() is already
held (but don't have to) so a separate mutex is preferable.

Signed-off-by: Benjamin Herrenschmidt <b...@kernel.crashing.org>
---
 drivers/pci/probe.c |  1 +
 include/linux/pci.h | 17 +++++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 440445ac7dfa..3ce287ab6150 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2155,6 +2155,7 @@ struct pci_dev *pci_alloc_dev(struct pci_bus *bus)
        INIT_LIST_HEAD(&dev->bus_list);
        dev->dev.type = &pci_dev_type;
        dev->bus = pci_bus_get(bus);
+       mutex_init(&dev->state_lock);
 
        return dev;
 }
diff --git a/include/linux/pci.h b/include/linux/pci.h
index f58bda204f09..0d4fc22df190 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -33,6 +33,7 @@
 #include <linux/io.h>
 #include <linux/resource_ext.h>
 #include <uapi/linux/pci.h>
+#include <linux/mutex.h>
 
 #include <linux/pci_ids.h>
 
@@ -443,8 +444,24 @@ struct pci_dev {
        phys_addr_t     rom;            /* Physical address if not from BAR */
        size_t          romlen;         /* Length if not from BAR */
        char            *driver_override; /* Driver name to force a match */
+
+       unsigned long   priv_flags;     /* Private flags for the PCI driver */
+
+       struct mutex    state_lock;     /* Protect local state bits */
+
+       /* --- Fields below this line are protected by the state_lock mutex */
 };
 
+static inline void pci_dev_state_lock(struct pci_dev *dev)
+{
+       mutex_lock(&dev->state_lock);
+}
+
+static inline void pci_dev_state_unlock(struct pci_dev *dev)
+{
+       mutex_unlock(&dev->state_lock);
+}
+
 static inline struct pci_dev *pci_physfn(struct pci_dev *dev)
 {
 #ifdef CONFIG_PCI_IOV
-- 
2.17.1