Re: [PATCH 1/4] scsi: ufs: atomic update for clkgating_enable

[Can Guo]

On 2020-10-06 06:36, Jaegeuk Kim wrote:
From: Jaegeuk Kim <jaeg...@google.com>
When giving a stress test which enables/disables clkgating, we hit 
device
timeout sometimes. This patch avoids subtle racy condition to address 
it.

Cc: Alim Akhtar <alim.akh...@samsung.com>
Cc: Avri Altman <avri.alt...@wdc.com>
Cc: Can Guo <c...@codeaurora.org>
Signed-off-by: Jaegeuk Kim <jaeg...@google.com>
---
 drivers/scsi/ufs/ufshcd.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
index 1d157ff58d817..d929c3d1e58cc 100644
--- a/drivers/scsi/ufs/ufshcd.c
+++ b/drivers/scsi/ufs/ufshcd.c
@@ -1791,19 +1791,19 @@ static ssize_t
ufshcd_clkgate_enable_store(struct device *dev,
                return -EINVAL;

        value = !!value;
+
+       spin_lock_irqsave(hba->host->host_lock, flags);
        if (value == hba->clk_gating.is_enabled)
                goto out;

-       if (value) {
-               ufshcd_release(hba);
-       } else {
-               spin_lock_irqsave(hba->host->host_lock, flags);
+       if (value)
+               hba->clk_gating.active_reqs--;
+       else
                hba->clk_gating.active_reqs++;
-               spin_unlock_irqrestore(hba->host->host_lock, flags);
-       }

        hba->clk_gating.is_enabled = value;
 out:
+       spin_unlock_irqrestore(hba->host->host_lock, flags);
        return count;
 }

I agree that we should protect the flag "is_enabled" with spin lock,
but I prefer the old logic of calling ufshcd_release() instead of
just doing hba->clk_gating.active_reqs--, you can use 
__ufshcd_release(),
which is free of locking.

Thanks,

Can Guo.