lkml.org 
[lkml]   [2021]   [Sep]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH] scsi: ufs: Fix a possible dead lock in clock scaling
Date
Assume a scenario where task A and B call ufshcd_devfreq_scale()
simultaneously. After task B calls downgrade_write() [1], but before it
calls down_read() [3], if task A calls down_write() [2], when task B calls
down_read() [3], it will lead to dead lock. Fix this by utilizing the
existing flag scaling.is_allowed to make sure only one task can do clock
scaling at a time.

Task A -
down_write [2]
ufshcd_clock_scaling_prepare
ufshcd_devfreq_scale
ufshcd_clkscale_enable_store

Task B -
down_read [3]
ufshcd_exec_dev_cmd
ufshcd_query_flag
ufshcd_wb_ctrl
downgrade_write [1]
ufshcd_devfreq_scale
ufshcd_devfreq_target
devfreq_set_target
update_devfreq
devfreq_performance_handler
governor_store

Fixes: 0e9d4ca43ba81 ("scsi: ufs: Protect some contexts from unexpected clock scaling")
Signed-off-by: Can Guo <cang@codeaurora.org>

diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
index 3841ab49..782a9c8 100644
--- a/drivers/scsi/ufs/ufshcd.c
+++ b/drivers/scsi/ufs/ufshcd.c
@@ -1186,6 +1186,7 @@ static int ufshcd_clock_scaling_prepare(struct ufs_hba *hba)
goto out;
}

+ hba->clk_scaling.is_allowed = false;
/* let's not get into low power until clock scaling is completed */
ufshcd_hold(hba, false);

@@ -1193,12 +1194,10 @@ static int ufshcd_clock_scaling_prepare(struct ufs_hba *hba)
return ret;
}

-static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba, bool writelock)
+static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba)
{
- if (writelock)
- up_write(&hba->clk_scaling_lock);
- else
- up_read(&hba->clk_scaling_lock);
+ hba->clk_scaling.is_allowed = true;
+ up_write(&hba->clk_scaling_lock);
ufshcd_scsi_unblock_requests(hba);
ufshcd_release(hba);
}
@@ -1215,7 +1214,6 @@ static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba, bool writelock)
static int ufshcd_devfreq_scale(struct ufs_hba *hba, bool scale_up)
{
int ret = 0;
- bool is_writelock = true;

ret = ufshcd_clock_scaling_prepare(hba);
if (ret)
@@ -1245,12 +1243,12 @@ static int ufshcd_devfreq_scale(struct ufs_hba *hba, bool scale_up)
}

/* Enable Write Booster if we have scaled up else disable it */
- downgrade_write(&hba->clk_scaling_lock);
- is_writelock = false;
+ up_write(&hba->clk_scaling_lock);
ufshcd_wb_toggle(hba, scale_up);
+ down_write(&hba->clk_scaling_lock);

out_unprepare:
- ufshcd_clock_scaling_unprepare(hba, is_writelock);
+ ufshcd_clock_scaling_unprepare(hba);
return ret;
}

--
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.
\
 
 \ /
  Last update: 2021-09-17 04:01    [W:0.110 / U:0.644 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site