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Message-ID: <5ce3b55b-3695-379a-1726-bf48aff3b4b9@ti.com>
Date: Mon, 21 Jun 2021 19:07:31 +0530
From: Kishon Vijay Abraham I <kishon@...com>
To: Vidya Sagar <vidyas@...dia.com>
CC: <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
Andrew Murray <amurray@...goodpenguin.co.uk>,
Bjorn Helgaas <bhelgaas@...gle.com>,
Athani Nadeem Ladkhan <nadeem@...ence.com>,
Tom Joseph <tjoseph@...ence.com>,
Manikanta Maddireddy <mmaddireddy@...dia.com>,
Om Prakash Singh <omp@...dia.com>,
Krishna Thota <kthota@...dia.com>
Subject: Re: [PATCH v2 2/5] PCI: endpoint: Replace spinlock with mutex
Hi Vidya Sagar,
On 21/06/21 3:08 pm, Vidya Sagar wrote:
>
>
> 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.
There could be two different functions trying to configure endpoint
controller (could be a multi-function endpoint) and the framework should
guarantee the hardware is not accessed by both the functions simultaneously.
> 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 can only protect within a function and not across multiple functions.
> 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.
Not sure what exactly the function driver does but can't map/unmap be
done for a big block once to optimize and operate on that buffer? I'd
assume you are having a custom driver on the host side too?
Thanks
Kishon
>
> 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@...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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