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

[Vidya Sagar <vidyas@xxxxxxxxxx>]

Hi Kishon,
Did you get time to look into it?

Thanks,
Vidya Sagar

On 6/11/2021 3:22 PM, Vidya Sagar wrote:
> 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