[Skiboot] [PATCH] core/lock.c: ensure valid start value for lock spin duration warning

[Stewart Smith]

The previous fix in a8e6cc3f4 only addressed half of the problem, as
we could also get an invalid value for start, causing us to fail
in a weird way.

This was caught by the testcases.OpTestHMIHandling.HMI_TFMR_ERRORS
test in op-test-framework.

You'd get to this part of the test and get the erroneous lock
spinning warnings:

PATH=/usr/local/sbin:$PATH putscom -c 00000000 0x2b010a84 0003080000000000
0000080000000000
[  790.140976993,4] WARNING: Lock has been spinning for 790275ms
[  790.140976993,4] WARNING: Lock has been spinning for 790275ms
[  790.140976918,4] WARNING: Lock has been spinning for 790275ms

This patch checks the validity of timebase before setting start,
and only checks the lock timeout if we got a valid start value.

Fixes: a8e6cc3f47525f86ef1d69d69a477b6264d0f8ee
Fixes: 84186ef0944c9413262f0974ddab3fb1343ccfe8
Signed-off-by: Stewart Smith <stewart at linux.vnet.ibm.com>
---
 core/lock.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/core/lock.c b/core/lock.c
index 620d26b21345..4ae3a213951c 100644
--- a/core/lock.c
+++ b/core/lock.c
@@ -206,7 +206,7 @@ bool try_lock_caller(struct lock *l, const char *owner)
 void lock_caller(struct lock *l, const char *owner)
 {
 	bool timeout_warn = false;
-	unsigned long start;
+	unsigned long start = 0;
 
 	if (bust_locks)
 		return;
@@ -218,7 +218,13 @@ void lock_caller(struct lock *l, const char *owner)
 	add_lock_request(l);
 
 #ifdef DEBUG_LOCKS
-	start = tb_to_msecs(mftb());
+	/*
+	 * Ensure that we get a valid start value
+	 * as we may be handling TFMR errors and taking
+	 * a lock to do so, so timebase could be garbage
+	 */
+	if( (mfspr(SPR_TFMR) & SPR_TFMR_TB_VALID))
+		start = tb_to_msecs(mftb());
 #endif
 
 	for (;;) {
@@ -229,7 +235,7 @@ void lock_caller(struct lock *l, const char *owner)
 			barrier();
 		smt_medium();
 
-		if (!timeout_warn)
+		if (start && !timeout_warn)
 			timeout_warn = lock_timeout(start);
 	}
 
-- 
2.14.3