Re: [PATCH 01/16] PCI/P2PDMA: Pass gfp_mask flags to upstream_bridge_distance_warn()

Logan Gunthorpe
2021-05-11T16:13:08Z

On 2021-05-11 10:05 a.m., Don Dutile wrote:
> On 5/1/21 11:58 PM, John Hubbard wrote:
>> On 4/8/21 10:01 AM, Logan Gunthorpe wrote:
>>> In order to call upstream_bridge_distance_warn() from a dma_map function,
>>> it must not sleep. The only reason it does sleep is to allocate the seqbuf
>>> to print which devices are within the ACS path.
>>>
>>> Switch the kmalloc call to use a passed in gfp_mask and don't print that
>>> message if the buffer fails to be allocated.
>>>
>>> Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
>>> Acked-by: Bjorn Helgaas <bhelgaas@google.com>
>>> ---
>>>   drivers/pci/p2pdma.c | 21 +++++++++++----------
>>>   1 file changed, 11 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
>>> index 196382630363..bd89437faf06 100644
>>> --- a/drivers/pci/p2pdma.c
>>> +++ b/drivers/pci/p2pdma.c
>>> @@ -267,7 +267,7 @@ static int pci_bridge_has_acs_redir(struct pci_dev *pdev)
>>>     static void seq_buf_print_bus_devfn(struct seq_buf *buf, struct pci_dev *pdev)
>>>   {
>>> -    if (!buf)
>>> +    if (!buf || !buf->buffer)
>>
>> This is not great, sort of from an overall design point of view, even though
>> it makes the rest of the patch work. See below for other ideas, that will
>> avoid the need for this sort of odd point fix.
>>
> +1.
> In fact, I didn't see how the kmalloc was changed... you refactored the code to pass-in the
> GFP_KERNEL that was originally hard-coded into upstream_bridge_distance_warn();
> I don't see how that avoided the kmalloc() call.
> in fact, I also see you lost a failed kmalloc() check, so it seems to have taken a step back.

I've changed this in v2 to just use some memory allocated on the stack.
Avoids this argument all together.

Logan