Re: [PATCH v2 2/5] PCI: endpoint: Replace spinlock with mutex

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Hi Kishon,
Apologies for bringup it up this late.
I'm wondering if there was any issue which this patch tried to address?
Actually, "The pci_epc_ops is not intended to be invoked from interrupt context" isn't true in case of Tegra194. We do call dw_pcie_ep_init_notify() API from threaded irq service routine and it eventually calls mutext_lock() of pci_epc_get_features() which is reusulting in the following warning log. BUG: sleeping function called from invalid context at kernel/locking/mutex.c: 
Would like hear your comments on it.

Thanks,
Vidya Sagar

On 2/12/2020 4:55 PM, Kishon Vijay Abraham I wrote:

External email: Use caution opening links or attachments


The pci_epc_ops is not intended to be invoked from interrupt context.
Hence replace spin_lock_irqsave and spin_unlock_irqrestore with
mutex_lock and mutex_unlock respectively.

Signed-off-by: Kishon Vijay Abraham I <kishon@xxxxxx>
---
  drivers/pci/endpoint/pci-epc-core.c | 82 +++++++++++------------------
  include/linux/pci-epc.h             |  6 +--
  2 files changed, 34 insertions(+), 54 deletions(-)

diff --git a/drivers/pci/endpoint/pci-epc-core.c b/drivers/pci/endpoint/pci-epc-core.c
index 2f6436599fcb..e51a12ed85bb 100644
--- a/drivers/pci/endpoint/pci-epc-core.c
+++ b/drivers/pci/endpoint/pci-epc-core.c
@@ -120,7 +120,6 @@ const struct pci_epc_features *pci_epc_get_features(struct pci_epc *epc,
                                                     u8 func_no)
  {
         const struct pci_epc_features *epc_features;
-       unsigned long flags;

         if (IS_ERR_OR_NULL(epc) || func_no >= epc->max_functions)
                 return NULL;
@@ -128,9 +127,9 @@ const struct pci_epc_features *pci_epc_get_features(struct pci_epc *epc,
         if (!epc->ops->get_features)
                 return NULL;

-       spin_lock_irqsave(&epc->lock, flags);
+       mutex_lock(&epc->lock);
         epc_features = epc->ops->get_features(epc, func_no);
-       spin_unlock_irqrestore(&epc->lock, flags);
+       mutex_unlock(&epc->lock);

         return epc_features;
  }
@@ -144,14 +143,12 @@ EXPORT_SYMBOL_GPL(pci_epc_get_features);
   */
  void pci_epc_stop(struct pci_epc *epc)
  {
-       unsigned long flags;
-
         if (IS_ERR(epc) || !epc->ops->stop)
                 return;

-       spin_lock_irqsave(&epc->lock, flags);
+       mutex_lock(&epc->lock);
         epc->ops->stop(epc);
-       spin_unlock_irqrestore(&epc->lock, flags);
+       mutex_unlock(&epc->lock);
  }
  EXPORT_SYMBOL_GPL(pci_epc_stop);

@@ -164,7 +161,6 @@ EXPORT_SYMBOL_GPL(pci_epc_stop);
  int pci_epc_start(struct pci_epc *epc)
  {
         int ret;
-       unsigned long flags;

         if (IS_ERR(epc))
                 return -EINVAL;
@@ -172,9 +168,9 @@ int pci_epc_start(struct pci_epc *epc)
         if (!epc->ops->start)
                 return 0;

-       spin_lock_irqsave(&epc->lock, flags);
+       mutex_lock(&epc->lock);
         ret = epc->ops->start(epc);
-       spin_unlock_irqrestore(&epc->lock, flags);
+       mutex_unlock(&epc->lock);

         return ret;
  }
@@ -193,7 +189,6 @@ int pci_epc_raise_irq(struct pci_epc *epc, u8 func_no,
                       enum pci_epc_irq_type type, u16 interrupt_num)
  {
         int ret;
-       unsigned long flags;

         if (IS_ERR_OR_NULL(epc) || func_no >= epc->max_functions)
                 return -EINVAL;
@@ -201,9 +196,9 @@ int pci_epc_raise_irq(struct pci_epc *epc, u8 func_no,
         if (!epc->ops->raise_irq)
                 return 0;

-       spin_lock_irqsave(&epc->lock, flags);
+       mutex_lock(&epc->lock);
         ret = epc->ops->raise_irq(epc, func_no, type, interrupt_num);
-       spin_unlock_irqrestore(&epc->lock, flags);
+       mutex_unlock(&epc->lock);

         return ret;
  }
@@ -219,7 +214,6 @@ EXPORT_SYMBOL_GPL(pci_epc_raise_irq);
  int pci_epc_get_msi(struct pci_epc *epc, u8 func_no)
  {
         int interrupt;
-       unsigned long flags;

         if (IS_ERR_OR_NULL(epc) || func_no >= epc->max_functions)
                 return 0;
@@ -227,9 +221,9 @@ int pci_epc_get_msi(struct pci_epc *epc, u8 func_no)
         if (!epc->ops->get_msi)
                 return 0;

-       spin_lock_irqsave(&epc->lock, flags);
+       mutex_lock(&epc->lock);
         interrupt = epc->ops->get_msi(epc, func_no);
-       spin_unlock_irqrestore(&epc->lock, flags);
+       mutex_unlock(&epc->lock);

         if (interrupt < 0)
                 return 0;
@@ -252,7 +246,6 @@ int pci_epc_set_msi(struct pci_epc *epc, u8 func_no, u8 interrupts)
  {
         int ret;
         u8 encode_int;
-       unsigned long flags;

         if (IS_ERR_OR_NULL(epc) || func_no >= epc->max_functions ||
             interrupts > 32)
@@ -263,9 +256,9 @@ int pci_epc_set_msi(struct pci_epc *epc, u8 func_no, u8 interrupts)

         encode_int = order_base_2(interrupts);

-       spin_lock_irqsave(&epc->lock, flags);
+       mutex_lock(&epc->lock);
         ret = epc->ops->set_msi(epc, func_no, encode_int);
-       spin_unlock_irqrestore(&epc->lock, flags);
+       mutex_unlock(&epc->lock);

         return ret;
  }
@@ -281,7 +274,6 @@ EXPORT_SYMBOL_GPL(pci_epc_set_msi);
  int pci_epc_get_msix(struct pci_epc *epc, u8 func_no)
  {
         int interrupt;
-       unsigned long flags;

         if (IS_ERR_OR_NULL(epc) || func_no >= epc->max_functions)
                 return 0;
@@ -289,9 +281,9 @@ int pci_epc_get_msix(struct pci_epc *epc, u8 func_no)
         if (!epc->ops->get_msix)
                 return 0;

-       spin_lock_irqsave(&epc->lock, flags);
+       mutex_lock(&epc->lock);
         interrupt = epc->ops->get_msix(epc, func_no);
-       spin_unlock_irqrestore(&epc->lock, flags);
+       mutex_unlock(&epc->lock);

         if (interrupt < 0)
                 return 0;
@@ -311,7 +303,6 @@ EXPORT_SYMBOL_GPL(pci_epc_get_msix);
  int pci_epc_set_msix(struct pci_epc *epc, u8 func_no, u16 interrupts)
  {
         int ret;
-       unsigned long flags;

         if (IS_ERR_OR_NULL(epc) || func_no >= epc->max_functions ||
             interrupts < 1 || interrupts > 2048)
@@ -320,9 +311,9 @@ int pci_epc_set_msix(struct pci_epc *epc, u8 func_no, u16 interrupts)
         if (!epc->ops->set_msix)
                 return 0;

-       spin_lock_irqsave(&epc->lock, flags);
+       mutex_lock(&epc->lock);
         ret = epc->ops->set_msix(epc, func_no, interrupts - 1);
-       spin_unlock_irqrestore(&epc->lock, flags);
+       mutex_unlock(&epc->lock);

         return ret;
  }
@@ -339,17 +330,15 @@ EXPORT_SYMBOL_GPL(pci_epc_set_msix);
  void pci_epc_unmap_addr(struct pci_epc *epc, u8 func_no,
                         phys_addr_t phys_addr)
  {
-       unsigned long flags;
-
         if (IS_ERR_OR_NULL(epc) || func_no >= epc->max_functions)
                 return;

         if (!epc->ops->unmap_addr)
                 return;

-       spin_lock_irqsave(&epc->lock, flags);
+       mutex_lock(&epc->lock);
         epc->ops->unmap_addr(epc, func_no, phys_addr);
-       spin_unlock_irqrestore(&epc->lock, flags);
+       mutex_unlock(&epc->lock);
  }
  EXPORT_SYMBOL_GPL(pci_epc_unmap_addr);

@@ -367,7 +356,6 @@ int pci_epc_map_addr(struct pci_epc *epc, u8 func_no,
                      phys_addr_t phys_addr, u64 pci_addr, size_t size)
  {
         int ret;
-       unsigned long flags;

         if (IS_ERR_OR_NULL(epc) || func_no >= epc->max_functions)
                 return -EINVAL;
@@ -375,9 +363,9 @@ int pci_epc_map_addr(struct pci_epc *epc, u8 func_no,
         if (!epc->ops->map_addr)
                 return 0;

-       spin_lock_irqsave(&epc->lock, flags);
+       mutex_lock(&epc->lock);
         ret = epc->ops->map_addr(epc, func_no, phys_addr, pci_addr, size);
-       spin_unlock_irqrestore(&epc->lock, flags);
+       mutex_unlock(&epc->lock);

         return ret;
  }
@@ -394,8 +382,6 @@ EXPORT_SYMBOL_GPL(pci_epc_map_addr);
  void pci_epc_clear_bar(struct pci_epc *epc, u8 func_no,
                        struct pci_epf_bar *epf_bar)
  {
-       unsigned long flags;
-
         if (IS_ERR_OR_NULL(epc) || func_no >= epc->max_functions ||
             (epf_bar->barno == BAR_5 &&
              epf_bar->flags & PCI_BASE_ADDRESS_MEM_TYPE_64))
@@ -404,9 +390,9 @@ void pci_epc_clear_bar(struct pci_epc *epc, u8 func_no,
         if (!epc->ops->clear_bar)
                 return;

-       spin_lock_irqsave(&epc->lock, flags);
+       mutex_lock(&epc->lock);
         epc->ops->clear_bar(epc, func_no, epf_bar);
-       spin_unlock_irqrestore(&epc->lock, flags);
+       mutex_unlock(&epc->lock);
  }
  EXPORT_SYMBOL_GPL(pci_epc_clear_bar);

@@ -422,7 +408,6 @@ int pci_epc_set_bar(struct pci_epc *epc, u8 func_no,
                     struct pci_epf_bar *epf_bar)
  {
         int ret;
-       unsigned long irq_flags;
         int flags = epf_bar->flags;

         if (IS_ERR_OR_NULL(epc) || func_no >= epc->max_functions ||
@@ -437,9 +422,9 @@ int pci_epc_set_bar(struct pci_epc *epc, u8 func_no,
         if (!epc->ops->set_bar)
                 return 0;

-       spin_lock_irqsave(&epc->lock, irq_flags);
+       mutex_lock(&epc->lock);
         ret = epc->ops->set_bar(epc, func_no, epf_bar);
-       spin_unlock_irqrestore(&epc->lock, irq_flags);
+       mutex_unlock(&epc->lock);

         return ret;
  }
@@ -460,7 +445,6 @@ int pci_epc_write_header(struct pci_epc *epc, u8 func_no,
                          struct pci_epf_header *header)
  {
         int ret;
-       unsigned long flags;

         if (IS_ERR_OR_NULL(epc) || func_no >= epc->max_functions)
                 return -EINVAL;
@@ -468,9 +452,9 @@ int pci_epc_write_header(struct pci_epc *epc, u8 func_no,
         if (!epc->ops->write_header)
                 return 0;

-       spin_lock_irqsave(&epc->lock, flags);
+       mutex_lock(&epc->lock);
         ret = epc->ops->write_header(epc, func_no, header);
-       spin_unlock_irqrestore(&epc->lock, flags);
+       mutex_unlock(&epc->lock);

         return ret;
  }
@@ -487,8 +471,6 @@ EXPORT_SYMBOL_GPL(pci_epc_write_header);
   */
  int pci_epc_add_epf(struct pci_epc *epc, struct pci_epf *epf)
  {
-       unsigned long flags;
-
         if (epf->epc)
                 return -EBUSY;

@@ -500,9 +482,9 @@ int pci_epc_add_epf(struct pci_epc *epc, struct pci_epf *epf)

         epf->epc = epc;

-       spin_lock_irqsave(&epc->lock, flags);
+       mutex_lock(&epc->lock);
         list_add_tail(&epf->list, &epc->pci_epf);
-       spin_unlock_irqrestore(&epc->lock, flags);
+       mutex_unlock(&epc->lock);

         return 0;
  }
@@ -517,15 +499,13 @@ EXPORT_SYMBOL_GPL(pci_epc_add_epf);
   */
  void pci_epc_remove_epf(struct pci_epc *epc, struct pci_epf *epf)
  {
-       unsigned long flags;
-
         if (!epc || IS_ERR(epc) || !epf)
                 return;

-       spin_lock_irqsave(&epc->lock, flags);
+       mutex_lock(&epc->lock);
         list_del(&epf->list);
         epf->epc = NULL;
-       spin_unlock_irqrestore(&epc->lock, flags);
+       mutex_unlock(&epc->lock);
  }
  EXPORT_SYMBOL_GPL(pci_epc_remove_epf);

@@ -604,7 +584,7 @@ __pci_epc_create(struct device *dev, const struct pci_epc_ops *ops,
                 goto err_ret;
         }

-       spin_lock_init(&epc->lock);
+       mutex_init(&epc->lock);
         INIT_LIST_HEAD(&epc->pci_epf);
         ATOMIC_INIT_NOTIFIER_HEAD(&epc->notifier);

diff --git a/include/linux/pci-epc.h b/include/linux/pci-epc.h
index 36644ccd32ac..9dd60f2e9705 100644
--- a/include/linux/pci-epc.h
+++ b/include/linux/pci-epc.h
@@ -88,7 +88,7 @@ struct pci_epc_mem {
   * @mem: address space of the endpoint controller
   * @max_functions: max number of functions that can be configured in this EPC
   * @group: configfs group representing the PCI EPC device
- * @lock: spinlock to protect pci_epc ops
+ * @lock: mutex to protect pci_epc ops
   * @notifier: used to notify EPF of any EPC events (like linkup)
   */
  struct pci_epc {
@@ -98,8 +98,8 @@ struct pci_epc {
         struct pci_epc_mem              *mem;
         u8                              max_functions;
         struct config_group             *group;
-       /* spinlock to protect against concurrent access of EP controller */
-       spinlock_t                      lock;
+       /* mutex to protect against concurrent access of EP controller */
+       struct mutex                    lock;
         struct atomic_notifier_head     notifier;
  };

--
2.17.1
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