linux-kernel - [PATCH] scsi: ufs: Make sure clk scaling happens only when hba is runtime ACTIVE

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Date:   Tue, 22 Sep 2020 00:09:04 -0700
From:   Can Guo <cang@...eaurora.org>
To:     asutoshd@...eaurora.org, nguyenb@...eaurora.org,
        hongwus@...eaurora.org, rnayak@...eaurora.org,
        linux-scsi@...r.kernel.org, kernel-team@...roid.com,
        saravanak@...gle.com, salyzyn@...gle.com, cang@...eaurora.org
Cc:     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>,
        Stanley Chu <stanley.chu@...iatek.com>,
        Bean Huo <beanhuo@...ron.com>,
        Bart Van Assche <bvanassche@....org>,
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] scsi: ufs: Make sure clk scaling happens only when hba is runtime ACTIVE

If someone plays with the UFS clk scaling devfreq governor through sysfs,
ufshcd_devfreq_scale may be called even when hba is not runtime ACTIVE,
which can lead to unexpected error. We cannot just protect it by calling
pm_runtime_get_sync, because that may cause racing problem since hba
runtime suspend ops needs to suspend clk scaling. In order to fix it, call
pm_runtime_get_noresume and check hba's runtime status, then only proceed
if hba is runtime ACTIVE, otherwise just bail.

governor_store
 devfreq_performance_handler
  update_devfreq
   devfreq_set_target
    ufshcd_devfreq_target
     ufshcd_devfreq_scale

Signed-off-by: Can Guo <cang@...eaurora.org>

diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
index e4cb994..847f355 100644
--- a/drivers/scsi/ufs/ufshcd.c
+++ b/drivers/scsi/ufs/ufshcd.c
@@ -1294,8 +1294,15 @@ static int ufshcd_devfreq_target(struct device *dev,
 	}
 	spin_unlock_irqrestore(hba->host->host_lock, irq_flags);
 
+	pm_runtime_get_noresume(hba->dev);
+	if (!pm_runtime_active(hba->dev)) {
+		pm_runtime_put_noidle(hba->dev);
+		ret = -EAGAIN;
+		goto out;
+	}
 	start = ktime_get();
 	ret = ufshcd_devfreq_scale(hba, scale_up);
+	pm_runtime_put(hba->dev);
 
 	trace_ufshcd_profile_clk_scaling(dev_name(hba->dev),
 		(scale_up ? "up" : "down"),
-- 
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