linux-kernel - Re: [PATCH v2 2/2] dmaengine: idxd: Fix refcount underflow on module unload

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Message-ID: <87h60j8bzj.fsf@intel.com>
Date: Fri, 13 Jun 2025 16:20:48 -0700
From: Vinicius Costa Gomes <vinicius.gomes@...el.com>
To: Yi Sun <yi.sun@...el.com>, dmaengine@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: yi.sun@...el.com, gordon.jin@...el.com
Subject: Re: [PATCH v2 2/2] dmaengine: idxd: Fix refcount underflow on
 module unload

Yi Sun <yi.sun@...el.com> writes:

> A recent refactor introduced a misplaced put_device() call, leading to a
> reference count underflow during module unload.
>
> There is no need to add additional put_device() calls for idxd groups,
> engines, or workqueues. Although commit a409e919ca3 claims:"Note, this
> also fixes the missing put_device() for idxd groups, engines, and wqs."
> It appears no such omission existed. The required cleanup is already
> handled by the call chain:
> idxd_unregister_devices() -> device_unregister() -> put_device()
>
> Extend idxd_cleanup() to perform the necessary cleanup, and remove
> idxd_cleanup_internals() which was not originally part of the driver
> unload path and introduced unintended reference count underflow.
>
> Fixes: a409e919ca32 ("dmaengine: idxd: Refactor remove call with idxd_cleanup() helper")
> Signed-off-by: Yi Sun <yi.sun@...el.com>
>
> diff --git a/drivers/dma/idxd/init.c b/drivers/dma/idxd/init.c
> index 504aca0fd597..a5eabeb6a8bd 100644
> --- a/drivers/dma/idxd/init.c
> +++ b/drivers/dma/idxd/init.c
> @@ -1321,7 +1321,12 @@ static void idxd_remove(struct pci_dev *pdev)
>  	device_unregister(idxd_confdev(idxd));
>  	idxd_shutdown(pdev);
>  	idxd_device_remove_debugfs(idxd);
> -	idxd_cleanup(idxd);
> +	perfmon_pmu_remove(idxd);
> +	idxd_cleanup_interrupts(idxd);
> +	if (device_pasid_enabled(idxd))
> +		idxd_disable_system_pasid(idxd);
> +	if (device_user_pasid_enabled(idxd))
> +		idxd_disable_sva(idxd->pdev);

idxd_disable_sva() got removed in commit 853b01b5efd7 ("dmaengine: idxd:
Remove unnecessary IOMMU_DEV_FEAT_IOPF")

>  	pci_iounmap(pdev, idxd->reg_base);
>  	put_device(idxd_confdev(idxd));
>  	pci_disable_device(pdev);
> -- 
> 2.43.0
>


Cheers,
-- 
Vinicius