linux-kernel - Re: [PATCH] scsi: ufs: mcq: Limit the amount of inflight requests

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Message-ID: <8cb5216b-7dee-a924-1362-88b53ecbe6ea@acm.org>
Date:   Thu, 30 Mar 2023 09:39:23 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Avri Altman <avri.altman@....com>,
        "James E . J . Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>
Cc:     Asutosh Das <quic_asutoshd@...cinc.com>, quic_cang@...cinc.com,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scsi: ufs: mcq: Limit the amount of inflight requests

On 3/30/23 06:11, Avri Altman wrote:
> diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
> index 35a3bd95c5e4..d529c42a682a 100644
> --- a/drivers/ufs/core/ufshcd.c
> +++ b/drivers/ufs/core/ufshcd.c
> @@ -8468,6 +8468,10 @@ static int ufshcd_alloc_mcq(struct ufs_hba *hba)
>   	if (ret)
>   		goto err;
>   
> +	if (WARN_ONCE(hba->nutrs * hba->nr_hw_queues > (1 << 16) - 1,
> +		     "there can be at most 1<<16 inflight requests\n"))
> +		goto err;
> +
>   	/*
>   	 * Previously allocated memory for nutrs may not be enough in MCQ mode.
>   	 * Number of supported tags in MCQ mode may be larger than SDB mode.

Hi Avri,

WARN*() should only be used to report kernel bugs. hba->nutrs * 
hba->nr_hw_queues being too large is not a kernel bug but a 
configuration issue.

Instead of failing MCQ allocation, shouldn't 
ufshcd_mcq_decide_queue_depth() be modified such that it restricts 
hba->nutrs to a value that can be supported?

Thanks,

Bart.