2020-11-06 17:03:54

by Logan Gunthorpe

Subject: [RFC PATCH 01/15] PCI/P2PDMA: Don't sleep in upstream_bridge_distance_warn()

In order to call this function from a dma_map function, it must not sleep.
The only reason it does sleep so to allocate the seqbuf to print
which devices are within the ACS path.

Switch the kmalloc call to use GFP_NOWAIT and simply not print that
message if the buffer fails to be allocated.

Signed-off-by: Logan Gunthorpe <[email protected]>
---
drivers/pci/p2pdma.c | 17 +++++++++--------
1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index de1c331dbed4..94583779c36e 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)
return;

seq_buf_printf(buf, "%s;", pci_name(pdev));
@@ -501,19 +501,20 @@ upstream_bridge_distance_warn(struct pci_dev *provider, struct pci_dev *client,
bool acs_redirects;
int ret;

- seq_buf_init(&acs_list, kmalloc(PAGE_SIZE, GFP_KERNEL), PAGE_SIZE);
- if (!acs_list.buffer)
- return -ENOMEM;
+ seq_buf_init(&acs_list, kmalloc(PAGE_SIZE, GFP_NOWAIT), PAGE_SIZE);

ret = upstream_bridge_distance(provider, client, dist, &acs_redirects,
&acs_list);
if (acs_redirects) {
pci_warn(client, "ACS redirect is set between the client and provider (%s)\n",
pci_name(provider));
- /* Drop final semicolon */
- acs_list.buffer[acs_list.len-1] = 0;
- pci_warn(client, "to disable ACS redirect for this path, add the kernel parameter: pci=disable_acs_redir=%s\n",
- acs_list.buffer);
+
+ if (acs_list.buffer) {
+ /* Drop final semicolon */
+ acs_list.buffer[acs_list.len - 1] = 0;
+ pci_warn(client, "to disable ACS redirect for this path, add the kernel parameter: pci=disable_acs_redir=%s\n",
+ acs_list.buffer);
+ }
}

if (ret == PCI_P2PDMA_MAP_NOT_SUPPORTED) {
--
2.20.1

2020-11-09 09:14:02

by Christoph Hellwig

Subject: Re: [RFC PATCH 01/15] PCI/P2PDMA: Don't sleep in upstream_bridge_distance_warn()

On Fri, Nov 06, 2020 at 10:00:22AM -0700, Logan Gunthorpe wrote:
> In order to call this function from a dma_map function, it must not sleep.
> The only reason it does sleep so to allocate the seqbuf to print
> which devices are within the ACS path.
>
> Switch the kmalloc call to use GFP_NOWAIT and simply not print that
> message if the buffer fails to be allocated.

Please pass in the actual gfp_t. Especially from an I/O path
GFP_NOWAIT is not the right gfp_t anyway, you probably want GFP_ATOMIC
there. But also for the path where we can sleep we should allow that.