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

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Date:   Mon, 13 Dec 2021 16:00:50 -0800
From:   Bart Van Assche <bvanassche@....org>
To:     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
Cc:     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 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);

  	return pending;

Thanks,

Bart.