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Subject: Re: [PATCH v2 2/5] PCI: endpoint: Replace spinlock with mutex
To:     Kishon Vijay Abraham I <kishon@ti.com>
CC:     <linux-pci@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        "Lorenzo Pieralisi" <lorenzo.pieralisi@arm.com>,
        Andrew Murray <amurray@thegoodpenguin.co.uk>,
        Bjorn Helgaas <bhelgaas@google.com>,
        "Athani Nadeem Ladkhan" <nadeem@cadence.com>,
        Tom Joseph <tjoseph@cadence.com>,
        Manikanta Maddireddy <mmaddireddy@nvidia.com>,
        Om Prakash Singh <omp@nvidia.com>,
        Krishna Thota <kthota@nvidia.com>
References: <20200212112514.2000-1-kishon@ti.com>
 <20200212112514.2000-3-kishon@ti.com>
From:   Vidya Sagar <vidyas@nvidia.com>
Message-ID: <901293cd-e67a-04a4-d61e-37a105c33d15@nvidia.com>
Date:   Fri, 11 Jun 2021 15:22:31 +0530
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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@ti.com>
> ---
>   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
>