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

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Message-ID: <aE0hAy9peorIdgqU@ysun46-mobl.ccr.corp.intel.com>
Date: Sat, 14 Jun 2025 15:13:07 +0800
From: Yi Sun <yi.sun@...el.com>
To: Vinicius Costa Gomes <vinicius.gomes@...el.com>
CC: <dmaengine@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<gordon.jin@...el.com>
Subject: Re: [PATCH v2 2/2] dmaengine: idxd: Fix refcount underflow on module
 unload

On 13.06.2025 16:20, Vinicius Costa Gomes wrote:
>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")
I get it, thanks Vinicius for the reminder. Will post another version.

Thanks
    --Sun, Yi