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SubjectRe: [PATCH RESEND] uio/uio_pci_generic: Introduce refcnt on open/release
On Thu, Mar 31, 2022 at 10:23:52AM +0800, Yao Hongbo wrote:
> If two userspace programs both open the PCI UIO fd, when one
> of the program exits uncleanly, the other will cause IO hang
> due to bus-mastering disabled.

With two programs poking at the same device, how is this ever
supposed to work even while both are alive?

> It's a common usage for spdk/dpdk to use UIO. So, introduce refcnt
> to avoid such problems.
>
> Fixes: 865a11f("uio/uio_pci_generic: Disable bus-mastering on release")
> Reported-by: Xiu Yang <yangxiu.yx@alibaba-inc.com>
> Signed-off-by: Yao Hongbo <yaohongbo@linux.alibaba.com>
> ---
> drivers/uio/uio_pci_generic.c | 16 +++++++++++++++-
> 1 file changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/uio/uio_pci_generic.c b/drivers/uio/uio_pci_generic.c
> index e03f9b5..8add2cf 100644
> --- a/drivers/uio/uio_pci_generic.c
> +++ b/drivers/uio/uio_pci_generic.c
> @@ -31,6 +31,7 @@
> struct uio_pci_generic_dev {
> struct uio_info info;
> struct pci_dev *pdev;
> + atomic_t refcnt;
> };
>
> static inline struct uio_pci_generic_dev *
> @@ -39,6 +40,14 @@ struct uio_pci_generic_dev {
> return container_of(info, struct uio_pci_generic_dev, info);
> }
>
> +static int open(struct uio_info *info, struct inode *inode)
> +{
> + struct uio_pci_generic_dev *gdev = to_uio_pci_generic_dev(info);
> +
> + atomic_inc(&gdev->refcnt);
> + return 0;
> +}
> +
> static int release(struct uio_info *info, struct inode *inode)
> {
> struct uio_pci_generic_dev *gdev = to_uio_pci_generic_dev(info);
> @@ -51,7 +60,9 @@ static int release(struct uio_info *info, struct inode *inode)
>  * Note that there's a non-zero chance doing this will wedge the device
>  * at least until reset.
> */
> - pci_clear_master(gdev->pdev);
> + if (atomic_dec_and_test(&gdev->refcnt))
> + pci_clear_master(gdev->pdev);
> +
> return 0;
> }
>
> @@ -92,8 +103,11 @@ static int probe(struct pci_dev *pdev,
>
> gdev->info.name = "uio_pci_generic";
> gdev->info.version = DRIVER_VERSION;
> + gdev->info.open = open;
> gdev->info.release = release;
> gdev->pdev = pdev;
> + atomic_set(&gdev->refcnt, 0);
> +
> if (pdev->irq && (pdev->irq != IRQ_NOTCONNECTED)) {
> gdev->info.irq = pdev->irq;
> gdev->info.irq_flags = IRQF_SHARED;
> --
> 1.8.3.1

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