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>

3 files changed, 9 insertions, 22 deletions

diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index 26dbdc37d219..fec596da9bd0 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -460,19 +460,6 @@ static int kgdb_reenter_check(struct kgdb_state *ks)
         return 1;
 }
 
-static void dbg_cpu_switch(int cpu, int next_cpu)
-{
-        /* Mark the cpu we are switching away from as a slave when it
-         * holds the kgdb_active token.  This must be done so that the
-         * that all the cpus wait in for the debug core will not enter
-         * again as the master. */
-        if (cpu == atomic_read(&kgdb_active)) {
-                kgdb_info[cpu].exception_state |= DCPU_IS_SLAVE;
-                kgdb_info[cpu].exception_state &= ~DCPU_WANT_MASTER;
-        }
-        kgdb_info[next_cpu].exception_state |= DCPU_NEXT_MASTER;
-}
-
 static void dbg_touch_watchdogs(void)
 {
         touch_softlockup_watchdog_sync();
@@ -638,7 +625,8 @@ cpu_master_loop:
                 if (error == DBG_PASS_EVENT) {
                         dbg_kdb_mode = !dbg_kdb_mode;
                 } else if (error == DBG_SWITCH_CPU_EVENT) {
-                        dbg_cpu_switch(cpu, dbg_switch_cpu);
+                        kgdb_info[dbg_switch_cpu].exception_state |=
+                                DCPU_NEXT_MASTER;
                         goto cpu_loop;
                 } else {
                         kgdb_info[cpu].ret_state = error;
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);