linux-kernel - [PATCH] soundwire: bus: Fix unbalanced pm_runtime

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Date:   Mon, 27 Feb 2023 11:29:33 +0000
From:   Richard Fitzgerald <rf@...nsource.cirrus.com>
To:     <vkoul@...nel.org>, <yung-chuan.liao@...ux.intel.com>,
        <pierre-louis.bossart@...ux.intel.com>, <sanyog.r.kale@...el.com>
CC:     <alsa-devel@...a-project.org>, <linux-kernel@...r.kernel.org>,
        <patches@...nsource.cirrus.com>,
        Richard Fitzgerald <rf@...nsource.cirrus.com>
Subject: [PATCH] soundwire: bus: Fix unbalanced pm_runtime_put() causing usage count underflow

This reverts commit
443a98e649b4 ("soundwire: bus: use pm_runtime_resume_and_get()")

Change calls to pm_runtime_resume_and_get() back to pm_runtime_get_sync().
This fixes a usage count underrun caused by doing a pm_runtime_put() even
though pm_runtime_resume_and_get() returned an error.

The three affected functions ignore -EACCES error from trying to get
pm_runtime, and carry on, including a put at the end of the function.
But pm_runtime_resume_and_get() does not increment the usage count if it
returns an error. So in the -EACCES case you must not call
pm_runtime_put().

The documentation for pm_runtime_get_sync() says:
 "Consider using pm_runtime_resume_and_get() ...  as this is likely to
 result in cleaner code."

In this case I don't think it results in cleaner code because the
pm_runtime_put() at the end of the function would have to be conditional on
the return value from pm_runtime_resume_and_get() at the top of the
function.

pm_runtime_get_sync() doesn't have this problem because it always
increments the count, so always needs a put. The code can just flow through
and do the pm_runtime_put() unconditionally.

Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
---
 drivers/soundwire/bus.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c
index 76515c33e639..4fd221d0cc81 100644
--- a/drivers/soundwire/bus.c
+++ b/drivers/soundwire/bus.c
@@ -571,9 +571,11 @@ int sdw_nread(struct sdw_slave *slave, u32 addr, size_t count, u8 *val)
 {
 	int ret;

-	ret = pm_runtime_resume_and_get(&slave->dev);
-	if (ret < 0 && ret != -EACCES)
+	ret = pm_runtime_get_sync(&slave->dev);
+	if (ret < 0 && ret != -EACCES) {
+		pm_runtime_put_noidle(&slave->dev);
 		return ret;
+	}

 	ret = sdw_nread_no_pm(slave, addr, count, val);

@@ -595,9 +597,11 @@ int sdw_nwrite(struct sdw_slave *slave, u32 addr, size_t count, const u8 *val)
 {
 	int ret;

-	ret = pm_runtime_resume_and_get(&slave->dev);
-	if (ret < 0 && ret != -EACCES)
+	ret = pm_runtime_get_sync(&slave->dev);
+	if (ret < 0 && ret != -EACCES) {
+		pm_runtime_put_noidle(&slave->dev);
 		return ret;
+	}

 	ret = sdw_nwrite_no_pm(slave, addr, count, val);

@@ -1565,9 +1569,10 @@ static int sdw_handle_slave_alerts(struct sdw_slave *slave)

 	sdw_modify_slave_status(slave, SDW_SLAVE_ALERT);

-	ret = pm_runtime_resume_and_get(&slave->dev);
+	ret = pm_runtime_get_sync(&slave->dev);
 	if (ret < 0 && ret != -EACCES) {
 		dev_err(&slave->dev, "Failed to resume device: %d\n", ret);
+		pm_runtime_put_noidle(&slave->dev);
 		return ret;
 	}

-- 
2.30.2