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

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