Re: [PATCH] scsi: ufs: fix livelock on ufshcd_clear_ua_wlun

[Stanley Chu <stanley.chu@mediatek.com>]

Hi Jaegeuk,

On Wed, 2020-12-16 at 11:02 -0800, Jaegeuk Kim wrote:
> From: Jaegeuk Kim <jaegeuk@google.com>
> 
> This fixes the below livelock which is caused by calling a scsi command before
> ufshcd_scsi_unblock_requests() in ufshcd_ungate_work().
> 
> Workqueue: ufs_clk_gating_0 ufshcd_ungate_work
> Call trace:
>  __switch_to+0x298/0x2bc
>  __schedule+0x59c/0x760
>  schedule+0xac/0xf0
>  schedule_timeout+0x44/0x1b4
>  io_schedule_timeout+0x44/0x68
>  wait_for_common_io+0x7c/0x100
>  wait_for_completion_io+0x14/0x20
>  blk_execute_rq+0x94/0xd0
>  __scsi_execute+0x100/0x1c0
>  ufshcd_clear_ua_wlun+0x124/0x1c8
>  ufshcd_host_reset_and_restore+0x1d0/0x2cc
>  ufshcd_link_recovery+0xac/0x134
>  ufshcd_uic_hibern8_exit+0x1e8/0x1f0
>  ufshcd_ungate_work+0xac/0x130

According to the latest mainstream kernel, once
ufshcd_uic_hibern8_exit() encounters error, instead, error handler work
will be scheduled without blocking ufshcd_uic_hibern8_exit(). In
addition, ufshcd_scsi_unblock_requests() would be invoked before leaving
ufshcd_uic_hibern8_exit(). So this stack is no longer existed.

Thanks,
Stanley Chu

>  process_one_work+0x270/0x47c
>  worker_thread+0x27c/0x4d8
>  kthread+0x13c/0x320
>  ret_from_fork+0x10/0x18
> 
> Fixes: 1918651f2d7e ("scsi: ufs: Clear UAC for RPMB after ufshcd resets")
> Signed-off-by: Jaegeuk Kim <jaegeuk@google.com>
> ---
>  drivers/scsi/ufs/ufshcd.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index e221add25a7e..b0998db1b781 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -1603,6 +1603,7 @@ static void ufshcd_ungate_work(struct work_struct *work)
>  	}
>  unblock_reqs:
>  	ufshcd_scsi_unblock_requests(hba);
> +	ufshcd_clear_ua_wluns(hba);
>  }
>  
>  /**
> @@ -6913,7 +6914,7 @@ static int ufshcd_host_reset_and_restore(struct ufs_hba *hba)
>  
>  	/* Establish the link again and restore the device */
>  	err = ufshcd_probe_hba(hba, false);
> -	if (!err)
> +	if (!err && !hba->clk_gating.is_suspended)
>  		ufshcd_clear_ua_wluns(hba);
>  out:
>  	if (err)
> @@ -8745,6 +8746,7 @@ static int ufshcd_suspend(struct ufs_hba *hba, enum ufs_pm_op pm_op)
>  		ufshcd_resume_clkscaling(hba);
>  	hba->clk_gating.is_suspended = false;
>  	hba->dev_info.b_rpm_dev_flush_capable = false;
> +	ufshcd_clear_ua_wluns(hba);
>  	ufshcd_release(hba);
>  out:
>  	if (hba->dev_info.b_rpm_dev_flush_capable) {
> @@ -8855,6 +8857,8 @@ static int ufshcd_resume(struct ufs_hba *hba, enum ufs_pm_op pm_op)
>  		cancel_delayed_work(&hba->rpm_dev_flush_recheck_work);
>  	}
>  
> +	ufshcd_clear_ua_wluns(hba);
> +
>  	/* Schedule clock gating in case of no access to UFS device yet */
>  	ufshcd_release(hba);
>