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Message-ID: <09f6c713-5ae6-035c-c0ab-a8bd0fac7a79@redhat.com>
Date: Tue, 11 May 2021 12:05:34 -0400
From: Don Dutile <ddutile@...hat.com>
To: Logan Gunthorpe <logang@...tatee.com>,
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
Cc: 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>,
John Hubbard <jhubbard@...dia.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>,
Bjorn Helgaas <helgaas@...nel.org>,
Ira Weiny <ira.weiny@...el.com>,
Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH 02/16] PCI/P2PDMA: Avoid pci_get_slot() which sleeps
On 4/8/21 1:01 PM, Logan Gunthorpe wrote:
> In order to use upstream_bridge_distance_warn() from a dma_map function,
> it must not sleep. However, pci_get_slot() takes the pci_bus_sem so it
> might sleep.
>
> In order to avoid this, try to get the host bridge's device from
> bus->self, and if that is not set, just get the first element in the
> device list. It should be impossible for the host bridge's device to
> go away while references are held on child devices, so the first element
> should not be able to change and, thus, this should be safe.
Bjorn:
Why wouldn't (shouldn't?) the bus->self field be set for a host bridge device?
Should this situation be repaired in the host-brige config/setup code elsewhere in the kernel.
... and here, a check-and-fail with info of what doesn't have it setup (another new pci function to do the check & prinfo), so it can point to the offending host-bridge, and thus, the code that needs to be updated?
> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
> ---
> drivers/pci/p2pdma.c | 14 ++++++++++++--
> 1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index bd89437faf06..473a08940fbc 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -311,16 +311,26 @@ static const struct pci_p2pdma_whitelist_entry {
> static bool __host_bridge_whitelist(struct pci_host_bridge *host,
> bool same_host_bridge)
> {
> - struct pci_dev *root = pci_get_slot(host->bus, PCI_DEVFN(0, 0));
> const struct pci_p2pdma_whitelist_entry *entry;
> + struct pci_dev *root = host->bus->self;
> unsigned short vendor, device;
>
> + /*
> + * This makes the assumption that the first device on the bus is the
> + * bridge itself and it has the devfn of 00.0. This assumption should
> + * hold for the devices in the white list above, and if there are cases
> + * where this isn't true they will have to be dealt with when such a
> + * case is added to the whitelist.
> + */
> if (!root)
> + root = list_first_entry_or_null(&host->bus->devices,
> + struct pci_dev, bus_list);
> +
> + if (!root || root->devfn)
> return false;
>
> vendor = root->vendor;
> device = root->device;
> - pci_dev_put(root);
>
> for (entry = pci_p2pdma_whitelist; entry->vendor; entry++) {
> if (vendor != entry->vendor || device != entry->device)
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