linux-kernel - Re: [PATCH] xen/pciback: don't call pcistub_device

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Message-ID: <7e50b6ec-2b84-f5d9-0b5d-bf6e5e83cc25@epam.com>
Date:   Tue, 28 Mar 2023 11:46:32 +0000
From:   Oleksandr Tyshchenko <Oleksandr_Tyshchenko@...m.com>
To:     Juergen Gross <jgross@...e.com>
CC:     Stefano Stabellini <sstabellini@...nel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        Dan Carpenter <error27@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xen/pciback: don't call pcistub_device_put() under lock



On 28.03.23 11:45, Juergen Gross wrote:

Hello Juergen

> pcistub_device_put() shouldn't be called under spinlock, as it can
> sleep.
> 
> For this reason pcistub_device_get_pci_dev() needs to be modified:
> instead of always calling pcistub_device_get() just do the call of
> pcistub_device_get() only if it is really needed. This removes the
> need to call pcistub_device_put().
> 
> Reported-by: Dan Carpenter <error27@...il.com>
> Link: https://urldefense.com/v3/__https://lore.kernel.org/lkml/Y*JUIl64UDmdkboh@kadam/__;Kw!!GF_29dbcQIUBPA!wO4HR1jCrDMOfB1Ih2qEZs2jnqcieZUZnc6cPwh7Ta8hiLRKwS1Gs-1tmQP-NuEYoz9LhYWI8aFazIwIa8Lh$ [lore[.]kernel[.]org]
> Signed-off-by: Juergen Gross <jgross@...e.com>


Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>

> ---
>   drivers/xen/xen-pciback/pci_stub.c | 6 ++----
>   1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/xen/xen-pciback/pci_stub.c b/drivers/xen/xen-pciback/pci_stub.c
> index bba527620507..e34b623e4b41 100644
> --- a/drivers/xen/xen-pciback/pci_stub.c
> +++ b/drivers/xen/xen-pciback/pci_stub.c
> @@ -194,8 +194,6 @@ static struct pci_dev *pcistub_device_get_pci_dev(struct xen_pcibk_device *pdev,
>   	struct pci_dev *pci_dev = NULL;
>   	unsigned long flags;
>   
> -	pcistub_device_get(psdev);
> -
>   	spin_lock_irqsave(&psdev->lock, flags);
>   	if (!psdev->pdev) {
>   		psdev->pdev = pdev;
> @@ -203,8 +201,8 @@ static struct pci_dev *pcistub_device_get_pci_dev(struct xen_pcibk_device *pdev,
>   	}
>   	spin_unlock_irqrestore(&psdev->lock, flags);
>   
> -	if (!pci_dev)
> -		pcistub_device_put(psdev);
> +	if (pci_dev)
> +		pcistub_device_get(psdev);
>   
>   	return pci_dev;
>   }