Commit e4ece59a authored by Logan Gunthorpe's avatar Logan Gunthorpe Committed by Bjorn Helgaas
Browse files

PCI/P2PDMA: Collect acs list in stack buffer to avoid sleeping 

In order to call the calc_map_type_and_dist_warn() function from a dma_map
operation, the function must not sleep. The only reason it sleeps is to
allocate memory for the seq_buf to print a verbose warning telling the user
how to disable ACS for that path.

Instead of allocating the memory with kmalloc(), allocate a smaller buffer
on the stack. A 128 byte buffer is enough to print 10 PCI device names. A
system with 10 bridge ports between two devices that have ACS enabled would
be unusually large, so this should still be a reasonable limit.

This also cleans up the awkward (and broken) return with -ENOMEM which
contradicts the return type and the caller was not prepared for.

Link: https://lore.kernel.org/r/20210610160609.28447-3-logang@deltatee.com


Signed-off-by: default avatarLogan Gunthorpe <logang@deltatee.com>
Signed-off-by: default avatarBjorn Helgaas <bhelgaas@google.com>
parent 6389d437

drivers/pci/p2pdma.c

+2 −5
Original line number Diff line number Diff line
@@ -502,11 +502,10 @@ calc_map_type_and_dist_warn(struct pci_dev *provider, struct pci_dev *client, 
{

	struct seq_buf acs_list;

	bool acs_redirects;

	char buf[128];

	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, buf, sizeof(buf));



	ret = calc_map_type_and_dist(provider, client, dist, &acs_redirects,

				     &acs_list);
@@ -524,8 +523,6 @@ calc_map_type_and_dist_warn(struct pci_dev *provider, struct pci_dev *client, 
			 pci_name(provider));

	}



	kfree(acs_list.buffer);



	return ret;

}