[PATCH 1/2] powerpc/kgdb: Fix a single stgep case of lazy IRQ

[Tiejun Chen]

When we're in kgdb_singlestep(), we have to work around to get
thread_info by copying from the kernel stack before calling
kgdb_handle_exception(), then copying it back afterwards.

But for PPC64, we have a lazy interrupt implementation. So after
copying thread info frome kernle stack, if we need to replay an
interrupt, we shouldn't restore that previous backup thread info
to make sure we can replay an interrupt lately with a proper
thread info.

This patch use __check_irq_replay() to guarantee this process.

Signed-off-by: Tiejun Chen <tiejun.chen at windriver.com>
---
 arch/powerpc/kernel/irq.c  |   12 +++++++++++-
 arch/powerpc/kernel/kgdb.c |    7 ++++---
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index 71413f4..a773789 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -332,7 +332,17 @@ bool prep_irq_for_idle(void)
 	return true;
 }
 
-#endif /* CONFIG_PPC64 */
+notrace unsigned int check_irq_replay(void)
+{
+	return __check_irq_replay();
+}
+#else /* CONFIG_PPC64 */
+notrace unsigned int check_irq_replay(void)
+{
+	return 0;
+}
+#endif /* !CONFIG_PPC64 */
+EXPORT_SYMBOL(check_irq_replay);
 
 int arch_show_interrupts(struct seq_file *p, int prec)
 {
diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c
index c470a40..c4af341 100644
--- a/arch/powerpc/kernel/kgdb.c
+++ b/arch/powerpc/kernel/kgdb.c
@@ -151,6 +151,7 @@ static int kgdb_handle_breakpoint(struct pt_regs *regs)
 	return 1;
 }
 
+extern notrace unsigned int check_irq_replay(void);
 static int kgdb_singlestep(struct pt_regs *regs)
 {
 	struct thread_info *thread_info, *exception_thread_info;
@@ -181,9 +182,9 @@ static int kgdb_singlestep(struct pt_regs *regs)
 
 	kgdb_handle_exception(0, SIGTRAP, 0, regs);
 
-	if (thread_info != exception_thread_info)
-		/* Restore current_thread_info lastly. */
-		memcpy(exception_thread_info, backup_current_thread_info, sizeof *thread_info);
+	if ((thread_info != exception_thread_info) && (!check_irq_replay()))
+		/* Restore current_thread_info lastly only if we don't replay interrupt. */
+			memcpy(exception_thread_info, backup_current_thread_info, sizeof *thread_info);
 
 	return 1;
 }
-- 
1.7.9.5