linux-kernel - Re: [RFC PATCH] vfio: type1: fix kthread use case

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Message-ID: <7ed25c44-bb51-2d8d-82d9-f11272f56424@web.de>
Date:   Mon, 6 Jul 2020 15:33:58 +0200
From:   Markus Elfring <Markus.Elfring@....de>
To:     Hillf Danton <hdanton@...a.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        iommu@...ts.linux-foundation.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org,
        Christoph Hellwig <hch@....de>,
        Jörg Rödel <joro@...tes.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Yan Zhao <yan.y.zhao@...el.com>
Subject: Re: [RFC PATCH] vfio: type1: fix kthread use case

>> Can it be helpful to convert initialisations for these variables
>> into later assignments?
>
> Perhaps. Then it looks like the below.


…
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -2798,9 +2798,12 @@ static int vfio_iommu_type1_dma_rw_chunk
…
> -	bool kthread = current->mm == NULL;
> +	bool kthread;
> +	bool use_mm;

I would prefer the following variable declarations then.

+	bool kthread, use_mm;


>  	size_t offset;
>
> +	kthread = current->flags & PF_KTHREAD;
> +	use_mm = current->mm == NULL;

I propose to move such assignments directly before the corresponding check.


…
>  	if (!mm)
>  		return -EPERM;


+	kthread = current->flags & PF_KTHREAD;
+	use_mm = !current->mm;

> -	if (kthread)
> +	if (kthread && use_mm)
>  		kthread_use_mm(mm);
…

Regards,
Markus