23.01.2022 19:49, Akhil R пишет:
>> 21.01.2022 19:24, Akhil R пишет:
>>>>>>>>> +static int tegra_dma_terminate_all(struct dma_chan *dc) {
>>>>>>>>> + struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc);
>>>>>>>>> + unsigned long flags;
>>>>>>>>> + LIST_HEAD(head);
>>>>>>>>> + int err;
>>>>>>>>> +
>>>>>>>>> + if (tdc->dma_desc) {
>>>>>>>>
>>>>>>>> Needs locking protection against racing with the interrupt handler.
>>>>>>> tegra_dma_stop_client() waits for the in-flight transfer to
>>>>>>> complete and prevents any additional transfer to start.
>>>>>>> Wouldn't it manage the race? Do you see any potential issue there?
>>>>>>
>>>>>> You should consider interrupt handler like a process running in a
>>>>>> parallel thread. The interrupt handler sets tdc->dma_desc to NULL,
>>>>>> hence you'll get NULL dereference in tegra_dma_stop_client().
>>>>>
>>>>> Is it better if I remove the below part from tegra_dma_stop_client()
>>>>> so that dma_desc is not accessed at all?
>>>>>
>>>>> + wcount = tdc_read(tdc, TEGRA_GPCDMA_CHAN_XFER_COUNT);
>>>>> + tdc->dma_desc->bytes_transferred +=
>>>>> + tdc->dma_desc->bytes_requested - (wcount * 4);
>>>>>
>>>>> Because I don't see a point in updating the value there. dma_desc is
>>>>> set to NULL in the next step in terminate_all() anyway.
>>>>
>>>> That isn't going help you much because you also can't release DMA
>>>> descriptor while interrupt handler still may be running and using
>>>> that descriptor.
>>>
>>> Does the below functions look good to resolve the issue, provided
>>> tegra_dma_stop_client() doesn't access dma_desc?
>>
>> Stop shall not race with the start.
>>
>>> +static int tegra_dma_terminate_all(struct dma_chan *dc) {
>>> + struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc);
>>> + unsigned long flags;
>>> + LIST_HEAD(head);
>>> + int err;
>>> +
>>> + err = tegra_dma_stop_client(tdc);
>>> + if (err)
>>> + return err;
>>> +
>>> + tegra_dma_stop(tdc);
>>> +
>>> + spin_lock_irqsave(&tdc->vc.lock, flags);
>>> + tegra_dma_sid_free(tdc);
>>> + tdc->dma_desc = NULL;
>>> +
>>> + vchan_get_all_descriptors(&tdc->vc, &head);
>>> + spin_unlock_irqrestore(&tdc->vc.lock, flags);
>>> +
>>> + vchan_dma_desc_free_list(&tdc->vc, &head);
>>> +
>>> + return 0;
>>> +}
>>>
>>> +static irqreturn_t tegra_dma_isr(int irq, void *dev_id) {
>>> + struct tegra_dma_channel *tdc = dev_id;
>>> + struct tegra_dma_desc *dma_desc = tdc->dma_desc;
>>> + struct tegra_dma_sg_req *sg_req;
>>> + u32 status;
>>> +
>>> + /* Check channel error status register */
>>> + status = tdc_read(tdc, TEGRA_GPCDMA_CHAN_ERR_STATUS);
>>> + if (status) {
>>> + tegra_dma_chan_decode_error(tdc, status);
>>> + tegra_dma_dump_chan_regs(tdc);
>>> + tdc_write(tdc, TEGRA_GPCDMA_CHAN_ERR_STATUS, 0xFFFFFFFF);
>>> + }
>>> +
>>> + status = tdc_read(tdc, TEGRA_GPCDMA_CHAN_STATUS);
>>> + if (!(status & TEGRA_GPCDMA_STATUS_ISE_EOC))
>>> + return IRQ_HANDLED;
>>> +
>>> + tdc_write(tdc, TEGRA_GPCDMA_CHAN_STATUS,
>>> + TEGRA_GPCDMA_STATUS_ISE_EOC);
>>> +
>>> + spin_lock(&tdc->vc.lock);
>>> + if (!dma_desc)
>> All checks and assignments must be done inside of critical section.
>
> Okay. So, the lock should be held throughout the function.
> Do you think tegra_dma_pause should also hold a lock
> and remove irq_synchronize? That function also writes
> to CSR register.
Interrupt handler shall not unpause channel in a case of race condition,
it should handle completed transfer and check whether channel is paused
before issuing next transfer.
So yes, pause also needs a lock.
