igc: fix lock order in igc_ptp_reset

Commit 1a931c4 ("igc: add lock preventing multiple simultaneous PTM
transactions") added a new mutex to protect concurrent PTM transactions.
This lock is acquired in igc_ptp_reset() in order to ensure the PTM
registers are properly disabled after a device reset.

The flow where the lock is acquired already holds a spinlock, so acquiring
a mutex leads to a sleep-while-locking bug, reported both by smatch,
and the kernel test robot.

The critical section in igc_ptp_reset() does correctly use the
readx_poll_timeout_atomic variants, but the standard PTM flow uses regular
sleeping variants. This makes converting the mutex to a spinlock a bit
tricky.

Instead, re-order the locking in igc_ptp_reset. Acquire the mutex first,
and then the tmreg_lock spinlock. This is safe because there is no other
ordering dependency on these locks, as this is the only place where both
locks were acquired simultaneously. Indeed, any other flow acquiring locks
in that order would be wrong regardless.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Fixes: 1a931c4 ("igc: add lock preventing multiple simultaneous PTM transactions")
Link: https://lore.kernel.org/intel-wired-lan/Z_-P-Hc1yxcw0lTB@stanley.mountain/
Link: https://lore.kernel.org/intel-wired-lan/202504211511.f7738f5d-lkp@intel.com/T/#u
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Reviewed-by: Vitaly Lifshits <vitaly.lifshits@intel.com>
Tested-by: Mor Bar-Gabay <morx.bar.gabay@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/igc/igc_ptp.c

@@ -1290,6 +1290,8 @@ void igc_ptp_reset(struct igc_adapter *adapter)
 	/* reset the tstamp_config */
 	igc_ptp_set_timestamp_mode(adapter, &adapter->tstamp_config);
 
+	mutex_lock(&adapter->ptm_lock);
+
 	spin_lock_irqsave(&adapter->tmreg_lock, flags);
 
 	switch (adapter->hw.mac.type) {
@@ -1308,7 +1310,6 @@ void igc_ptp_reset(struct igc_adapter *adapter)
 		if (!igc_is_crosststamp_supported(adapter))
 			break;
 
-		mutex_lock(&adapter->ptm_lock);
 		wr32(IGC_PCIE_DIG_DELAY, IGC_PCIE_DIG_DELAY_DEFAULT);
 		wr32(IGC_PCIE_PHY_DELAY, IGC_PCIE_PHY_DELAY_DEFAULT);
 
@@ -1332,7 +1333,6 @@ void igc_ptp_reset(struct igc_adapter *adapter)
 			netdev_err(adapter->netdev, "Timeout reading IGC_PTM_STAT register\n");
 
 		igc_ptm_reset(hw);
-		mutex_unlock(&adapter->ptm_lock);
 		break;
 	default:
 		/* No work to do. */
@@ -1349,5 +1349,7 @@ void igc_ptp_reset(struct igc_adapter *adapter)
 out:
 	spin_unlock_irqrestore(&adapter->tmreg_lock, flags);
 
+	mutex_unlock(&adapter->ptm_lock);
+
 	wrfl();
 }