linux-kernel - Re: [PATCH v2 1/2] scsi: ufs: mcq: Fix the incorrect OCS value for the device command

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Date:   Sun, 11 Jun 2023 06:59:24 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Po-Wen Kao <powen.kao@...iatek.com>, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
Cc:     wsd_upstream@...iatek.com, peter.wang@...iatek.com,
        stanley.chu@...iatek.com, alice.chao@...iatek.com,
        naomi.chu@...iatek.com, chun-hung.wu@...iatek.com,
        cc.chou@...iatek.com, eddie.huang@...iatek.com
Subject: Re: [PATCH v2 1/2] scsi: ufs: mcq: Fix the incorrect OCS value for
 the device command

On 6/9/23 19:15, Po-Wen Kao wrote:
> From: Stanley Chu <stanley.chu@...iatek.com>
> 
> In MCQ mode, when a device command uses a hardware queue shared
> with other commands, a race condition may occur in the following scenario:
> 
> 1. A device command is completed in CQx with CQE entry "e".
> 2. The interrupt handler copies the "cqe" pointer to "hba->dev_cmd.cqe"
>     and completes "hba->dev_cmd.complete".
> 3. The "ufshcd_wait_for_dev_cmd()" function is awakened and retrieves
>     the OCS value from "hba->dev_cmd.cqe".
> 
> However, there is a possibility that the CQE entry "e" will be overwritten
> by newly completed commands in CQx, resulting in an incorrect OCS value
> being received by "ufshcd_wait_for_dev_cmd()".
> 
> To avoid this race condition, the OCS value should be immediately copied
> to the struct "lrb" of the device command. Then "ufshcd_wait_for_dev_cmd()"
> can retrieve the OCS value from the struct "lrb".

Since with this patch applied ufs_dev_cmd.cqe is always NULL, please 
remove the 'cqe' member from struct ufs_dev_cmd.

Thanks,

Bart.