linux-kernel - Re: [RFC PATCH v2 01/11] PCI/P2PDMA: Pass gfp_mask flags to upstream_bridge_distance

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Date:   Fri, 12 Mar 2021 14:39:36 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-block@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org,
        Stephen Bates <sbates@...thlin.com>,
        Christoph Hellwig <hch@....de>,
        Dan Williams <dan.j.williams@...el.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Christian König <christian.koenig@....com>,
        Ira Weiny <iweiny@...el.com>,
        John Hubbard <jhubbard@...dia.com>,
        Don Dutile <ddutile@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Jakowski Andrzej <andrzej.jakowski@...el.com>,
        Minturn Dave B <dave.b.minturn@...el.com>,
        Jason Ekstrand <jason@...kstrand.net>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Xiong Jianxin <jianxin.xiong@...el.com>
Subject: Re: [RFC PATCH v2 01/11] PCI/P2PDMA: Pass gfp_mask flags to
 upstream_bridge_distance_warn()

On Thu, Mar 11, 2021 at 04:31:31PM -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.

s/this function/upstream_bridge_distance_warn()/ ?
s/so to/is to/

Maybe the subject could say something about the purpose, e.g., allow
calling from atomic context or something?  "Pass gfp_mask flags" sort
of restates what we can read from the patch, but without the
motivation of why this is useful.

> 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@...tatee.com>

Acked-by: Bjorn Helgaas <bhelgaas@...gle.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)
>  		return;
>  
>  	seq_buf_printf(buf, "%s;", pci_name(pdev));
> @@ -495,25 +495,26 @@ upstream_bridge_distance(struct pci_dev *provider, struct pci_dev *client,
>  
>  static enum pci_p2pdma_map_type
>  upstream_bridge_distance_warn(struct pci_dev *provider, struct pci_dev *client,
> -			      int *dist)
> +			      int *dist, gfp_t gfp_mask)
>  {
>  	struct seq_buf acs_list;
>  	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_mask), 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) {
> @@ -566,7 +567,7 @@ int pci_p2pdma_distance_many(struct pci_dev *provider, struct device **clients,
>  
>  		if (verbose)
>  			ret = upstream_bridge_distance_warn(provider,
> -					pci_client, &distance);
> +					pci_client, &distance, GFP_KERNEL);
>  		else
>  			ret = upstream_bridge_distance(provider, pci_client,
>  						       &distance, NULL, NULL);
> -- 
> 2.20.1
>