cpu: add debug check in cpu_relax

If cpu_relax() is called when not at medium SMT priority, it will lose
the prior priority and return at medium. Add a debug check to catch
this, which would have flagged the previous bug.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Vasant Hegde <hegdevasant@linux.vnet.ibm.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/core/cpu.c b/core/cpu.c
index 5c10fc6..0f2da15 100644
--- a/core/cpu.c
+++ b/core/cpu.c
@@ -80,6 +80,12 @@ unsigned long __attrconst cpu_emergency_stack_top(unsigned int pir)
 
 void __nomcount cpu_relax(void)
 {
+	if ((mfspr(SPR_PPR32) >> 18) != 0x4) {
+		printf("cpu_relax called when not at medium SMT priority: "
+			"PPR[PRI]=0x%lx\n", mfspr(SPR_PPR32) >> 18);
+		backtrace();
+	}
+
 	/* Relax a bit to give sibling threads some breathing space */
 	smt_lowest();
 	asm volatile("nop; nop; nop; nop;\n"