linux-kernel - Re: [PATCH v1] scsi: ufs: Fix deadlock issue in ufshcd_wait_for_doorbell

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Date:   Mon, 13 Dec 2021 20:55:39 -0800
From:   John Stultz <john.stultz@...aro.org>
To:     Bart Van Assche <bvanassche@....org>
Cc:     Bean Huo <huobean@...il.com>, alim.akhtar@...sung.com,
        avri.altman@....com, asutoshd@...eaurora.org, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, stanley.chu@...iatek.com,
        beanhuo@...ron.com, tomas.winkler@...el.com, cang@...eaurora.org,
        daejun7.park@...sung.com, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] scsi: ufs: Fix deadlock issue in ufshcd_wait_for_doorbell_clr()

On Mon, Dec 13, 2021 at 8:15 PM Bart Van Assche <bvanassche@....org> wrote:
>
> On 12/13/21 3:00 PM, Bean Huo wrote:
> > Call shost_for_each_device() with host->host_lock is held will cause
> > a deadlock situation, which will cause the system to stall (the log
> > as follow). Fix this issue by narrowing the scope of the lock.
>
> Hi Bean,
>
> As you probably know I do not have access to a test setup that supports clock
> scaling. Has the following patch been considered?
>
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index 6d692aae67ce..244eddf0caf8 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -1084,7 +1084,9 @@ static u32 ufshcd_pending_cmds(struct ufs_hba *hba)
>         struct scsi_device *sdev;
>         u32 pending = 0;
>
> -       shost_for_each_device(sdev, hba->host)
> +       lockdep_assert_held(hba->host->host_lock);
> +
> +       __shost_for_each_device(sdev, hba->host)
>                 pending += sbitmap_weight(&sdev->budget_map);

We hit the same issue today as well, and this solution works on db845c.

Reported-by: YongQin Liu <yongqin.liu@...aro.org>
Reported-by: Amit Pundir <amit.pundir@...aro.org>
Tested-by: John Stultz <john.stultz@...aro.org>

thanks
-john