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

[Vidya Sagar <vidyas@nvidia.com>]

On 6/21/2021 10:44 AM, Kishon Vijay Abraham I wrote:
> External email: Use caution opening links or attachments
> 
> 
> Hi Vidya Sagar,
> 
> On 11/06/21 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?
> 
> There was one function pci_epc_linkup() which was expected to be invoked
> in interrupt context (basically when the LINKUP interrupt is raised).
> But after it was moved to use atomic notifier, all the EPC core APIs
> were replaced to use mutex.
>> 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.
After reviewing the logs and code again, I think it was my mistake to 
come to early conclusion that it was because of calling mutex_lock() in 
the atomic context. It is clear now.

I would like to understand the reason behind putting locks in the epc 
core driver before calling ops.
I believe the ops callers should implement lock if they are concurrently 
accessing the ops instead of adding a global lock in the epc core.
This would help in scenarios like the one below.

	We have a performance oriented endpoint function driver which calls 
map, unmap & raise_irq ops from softirq context and because of 
mutex_lock(), we can't do that now. epc core driver should not restrict 
the function drivers to use only non-atomic functions.

Thanks,
Vidya Sagar
> 
> I don't think it is ideal to initialize EPC in interrupt context (unless
> there is a specific reason for it). EPC initialization can be moved to
> bottom half similar to how commands are handled after LINKUP.

> 
> Thanks
> Kishon
> 
>>
>> 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
>>>