powerpc/ppc32/tracing: Add stack frame to calls of trace_hardirqs_on/off

32-bit variant of the previous patch for 64-bit:

<<
    When an interrupt occurs in userspace, we can call trace_hardirqs_on/off()
    With one level stack. But if we have irqsoff tracing enabled,
    it checks both CALLER_ADDR0 and CALLER_ADDR1. The second call
    goes two stack frames up. If this is from user space, then there may
    not exist a second stack....
>>

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index c22dc1ec1c94..56212bc0ab08 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -880,7 +880,18 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_TYPE_47x)
          */
         andi.   r10,r9,MSR_EE
         beq     1f
+        /*
+         * Since the ftrace irqsoff latency trace checks CALLER_ADDR1,
+         * which is the stack frame here, we need to force a stack frame
+         * in case we came from user space.
+         */
+        stwu    r1,-32(r1)
+        mflr    r0
+        stw     r0,4(r1)
+        stwu    r1,-32(r1)
         bl      trace_hardirqs_on
+        lwz     r1,0(r1)
+        lwz     r1,0(r1)
         lwz     r9,_MSR(r1)
 1:
 #endif /* CONFIG_TRACE_IRQFLAGS */