e1000e: debug contention on NVM SWFLAG

This patch adds a mutex to the e1000e driver that would help
catch any collisions of two e1000e threads accessing hardware
at the same time.

description and patch updated by Jesse

Signed-off-by: Thomas Gleixner <[e-mail]>
Signed-off-by: Jesse Brandeburg <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/net/e1000e/ich8lan.c

···
 	return 0;
 }
 
+static DEFINE_MUTEX(nvm_mutex);
+static pid_t nvm_owner = -1;
+
 /**
  *  e1000_acquire_swflag_ich8lan - Acquire software control flag
  *  @hw: pointer to the HW structure
···
 {
 	u32 extcnf_ctrl;
 	u32 timeout = PHY_CFG_TIMEOUT;
+
+	WARN_ON(preempt_count());
+
+	if (!mutex_trylock(&nvm_mutex)) {
+		WARN(1, KERN_ERR "e1000e mutex contention. Owned by pid %d\n",
+		     nvm_owner);
+		mutex_lock(&nvm_mutex);
+	}
+	nvm_owner = current->pid;
 
 	while (timeout) {
 		extcnf_ctrl = er32(EXTCNF_CTRL);
···
 
 	if (!timeout) {
 		hw_dbg(hw, "FW or HW has locked the resource for too long.\n");
+		nvm_owner = -1;
+		mutex_unlock(&nvm_mutex);
 		return -E1000_ERR_CONFIG;
 	}
 
···
 	extcnf_ctrl = er32(EXTCNF_CTRL);
 	extcnf_ctrl &= ~E1000_EXTCNF_CTRL_SWFLAG;
 	ew32(EXTCNF_CTRL, extcnf_ctrl);
+
+	nvm_owner = -1;
+	mutex_unlock(&nvm_mutex);
 }
 
 /**