pse_ethtool_set_pw_limit() checks whether the PI is powered without
pcdev->lock. pse_isr() changes that state under the lock, so if the PD
disconnects in between, budget is reserved for a port that is no longer
powered.

Do the check in pse_pi_update_pw_budget() under the lock, and report
whether the budget was changed, so the rollback after a failed
regulator_set_current_limit() runs only then. This also rolls back a
budget that started from zero, which the old code skipped.

Found by code inspection. Not reproduced.

Fixes: ffef61d6d273 ("net: pse-pd: Add support for budget evaluation strategies")
Reviewed-by: Kory Maincent <kory.maincent@bootlin.com>
Acked-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Carlo Szelinsky <github@szelinsky.de>
---
 drivers/net/pse-pd/pse_core.c | 39 ++++++++++++++++++++++-------------
 1 file changed, 25 insertions(+), 14 deletions(-)

diff --git a/drivers/net/pse-pd/pse_core.c b/drivers/net/pse-pd/pse_core.c
index 44bc6d557965..7fffe7e16f75 100644
--- a/drivers/net/pse-pd/pse_core.c
+++ b/drivers/net/pse-pd/pse_core.c
@@ -1815,22 +1815,35 @@ EXPORT_SYMBOL_GPL(pse_ethtool_set_config);
  * @pcdev: a pointer to the PSE controller device
  * @id: index of the PSE PI
  * @pw_req: power requested
+ * @updated: set to true if the budget was changed
  * @extack: extack for reporting useful error messages
  *
- * Return: Previous power allocated on success and failure value on error
+ * Return: Power allocated before the update, or a negative error code.
+ *	   0 is also returned when the budget was not changed, so callers
+ *	   check @updated before they roll back.
  */
 static int pse_pi_update_pw_budget(struct pse_controller_dev *pcdev, int id,
-				   const unsigned int pw_req,
+				   const unsigned int pw_req, bool *updated,
 				   struct netlink_ext_ack *extack)
 {
 	struct pse_pi *pi = &pcdev->pi[id];
 	int previous_pw_allocated;
 	int pw_diff, ret = 0;
 
+	*updated = false;
+
 	/* We don't want pw_allocated_mW value change in the middle of an
 	 * power budget update
 	 */
 	mutex_lock(&pcdev->lock);
+	/* Only a PI under software power control that is enabled and has a
+	 * PD detected gets a budget. Check this here, as pse_isr() changes
+	 * it under the same lock.
+	 */
+	if (!pse_pw_d_is_sw_pw_control(pcdev, pi->pw_d) ||
+	    !pi->admin_state_enabled || !pi->isr_pd_detected)
+		goto out;
+
 	previous_pw_allocated = pi->pw_allocated_mW;
 	pw_diff = pw_req - previous_pw_allocated;
 	if (!pw_diff) {
@@ -1848,6 +1861,7 @@ static int pse_pi_update_pw_budget(struct pse_controller_dev *pcdev, int id,
 		regulator_free_power_budget(pi->pw_d->supply, -pw_diff);
 	}
 	pi->pw_allocated_mW = pw_req;
+	*updated = true;
 	ret = previous_pw_allocated;
 
 out:
@@ -1868,6 +1882,7 @@ int pse_ethtool_set_pw_limit(struct pse_control *psec,
 			     const unsigned int pw_limit)
 {
 	int uV, uA, ret, previous_pw_allocated = 0;
+	bool updated;
 	s64 tmp_64;
 
 	if (pw_limit > MAX_PI_PW)
@@ -1894,21 +1909,17 @@ int pse_ethtool_set_pw_limit(struct pse_control *psec,
 	/* Update power budget only in software power control case and
 	 * if a Power Device is powered.
 	 */
-	if (pse_pw_d_is_sw_pw_control(psec->pcdev,
-				      psec->pcdev->pi[psec->id].pw_d) &&
-	    psec->pcdev->pi[psec->id].admin_state_enabled &&
-	    psec->pcdev->pi[psec->id].isr_pd_detected) {
-		ret = pse_pi_update_pw_budget(psec->pcdev, psec->id,
-					      pw_limit, extack);
-		if (ret < 0)
-			return ret;
-		previous_pw_allocated = ret;
-	}
+	ret = pse_pi_update_pw_budget(psec->pcdev, psec->id, pw_limit,
+				      &updated, extack);
+	if (ret < 0)
+		return ret;
+	previous_pw_allocated = ret;
 
 	ret = regulator_set_current_limit(psec->ps, 0, uA);
-	if (ret < 0 && previous_pw_allocated) {
+	if (ret < 0 && updated) {
 		pse_pi_update_pw_budget(psec->pcdev, psec->id,
-					previous_pw_allocated, extack);
+					previous_pw_allocated, &updated,
+					extack);
 	}
 
 	return ret;
-- 
2.43.0