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

Don Dutile
2021-05-11T16:23:38Z

On 5/11/21 12:12 PM, Logan Gunthorpe wrote:
>
> 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
>
Looking fwd to the v2; again, my apologies for the delay, and the redundancy it's adding to your feedback review & changes.
-Don