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

[Logan Gunthorpe]

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 <logang@xxxxxxxxxxxx>
---
 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