kdb,debug_core: adjust master cpu switch logic against new debug_core locking

The kdb shell needs to enforce switching back to the original CPU that
took the exception before restoring normal kernel execution.  Resuming
from a different CPU than what took the original exception will cause
problems with spin locks that are freed from the a different processor
than had taken the lock.

The special logic in dbg_cpu_switch() can go away entirely with
because the state of what cpus want to be masters or slaves will
remain unchanged between entry and exit of the debug_core exception
context.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

2 files changed, 7 insertions, 8 deletions

diff --git a/kernel/debug/kdb/kdb_debugger.c b/kernel/debug/kdb/kdb_debugger.c
index bf6e8270e957..dd0b1b7dd02c 100644
--- a/kernel/debug/kdb/kdb_debugger.c
+++ b/kernel/debug/kdb/kdb_debugger.c
@@ -86,7 +86,7 @@ int kdb_stub(struct kgdb_state *ks)
 	}
 	/* Set initial kdb state variables */
 	KDB_STATE_CLEAR(KGDB_TRANS);
-	kdb_initial_cpu = ks->cpu;
+	kdb_initial_cpu = atomic_read(&kgdb_active);
 	kdb_current_task = kgdb_info[ks->cpu].task;
 	kdb_current_regs = kgdb_info[ks->cpu].debuggerinfo;
 	/* Remove any breakpoints as needed by kdb and clear single step */
@@ -105,7 +105,6 @@ int kdb_stub(struct kgdb_state *ks)
 		ks->pass_exception = 1;
 		KDB_FLAG_SET(CATASTROPHIC);
 	}
-	kdb_initial_cpu = ks->cpu;
 	if (KDB_STATE(SSBPT) && reason == KDB_REASON_SSTEP) {
 		KDB_STATE_CLEAR(SSBPT);
 		KDB_STATE_CLEAR(DOING_SS);
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 4226f32517d1..d7bda21a106b 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -1749,13 +1749,13 @@ static int kdb_go(int argc, const char **argv)
 	int nextarg;
 	long offset;
 
+	if (raw_smp_processor_id() != kdb_initial_cpu) {
+		kdb_printf("go must execute on the entry cpu, "
+			   "please use \"cpu %d\" and then execute go\n",
+			   kdb_initial_cpu);
+		return KDB_BADCPUNUM;
+	}
 	if (argc == 1) {
-		if (raw_smp_processor_id() != kdb_initial_cpu) {
-			kdb_printf("go <address> must be issued from the "
-				   "initial cpu, do cpu %d first\n",
-				   kdb_initial_cpu);
-			return KDB_ARGCOUNT;
-		}
 		nextarg = 1;
 		diag = kdbgetaddrarg(argc, argv, &nextarg,
 				     &addr, &offset, NULL);