[PATCH 9/9] coresight: etm3x: Prohibit modifying seq_curr_state while session is enabled

[James Clark]

When a sysfs session is disabled, seq_curr_state is read back from the
hardware into sysfs_config, overwriting any value written while the
session was enabled. Return -EBUSY in that case.

Do the mode check and the write under drvdata->spinlock. etm_enable_sysfs()
takes the mode before copying sysfs_config to curr_config under the same
lock, so either the new value is included in the copy, or the store sees
that the session is enabled. etm_disable_sysfs() does the read back before
releasing the mode, so a store can't succeed until it's done.

Fixes: a939fc5a71ad ("coresight-etm: add CoreSight ETM/PTM driver")
Reported-by: Sashiko <sashiko-bot@xxxxxxxxxx>
Closes: https://sashiko.dev/#/bug/linux-d70beb3d-d997-429d-9828-d396e1bbfbb5
Signed-off-by: James Clark <james.clark@xxxxxxxxxx>
---
 drivers/hwtracing/coresight/coresight-etm3x-sysfs.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c b/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
index d185fb8270e1..08c10fd146d5 100644
--- a/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
+++ b/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
@@ -1014,6 +1014,11 @@ static ssize_t seq_curr_state_store(struct device *dev,
 	if (val > ETM_SEQ_STATE_MAX_VAL)
 		return -EINVAL;
 
+	guard(spinlock)(&drvdata->spinlock);
+	if (IS_ERR_OR_NULL(drvdata->csdev) ||
+	    coresight_get_mode(drvdata->csdev) == CS_MODE_SYSFS)
+		return -EBUSY;
+
 	sysfs_config->seq_curr_state = val;
 
 	return size;

-- 
2.43.0