kgdb: eliminate kgdb_wait(), all cpus enter the same way

This is a kgdb architectural change to have all the cpus (master or
slave) enter the same function.

A cpu that hits an exception (wants to be the master cpu) will call
kgdb_handle_exception() from the trap handler and then invoke a
kgdb_roundup_cpu() to synchronize the other cpus and bring them into
the kgdb_handle_exception() as well.

A slave cpu will enter kgdb_handle_exception() from the
kgdb_nmicallback() and set the exception state to note that the
processor is a slave.

Previously the salve cpu would have called kgdb_wait().  This change
allows the debug core to change cpus without resuming the system in
order to inspect arch specific cpu information.

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

diff --git a/kernel/kgdb.c b/kernel/kgdb.c
index 42fd128..6882c04 100644 (file)
--- a/kernel/kgdb.c
+++ b/kernel/kgdb.c
@@ -69,9 +69,16 @@ struct kgdb_state {
        struct pt_regs          *linux_regs;
 };
 
+/* Exception state values */
+#define DCPU_WANT_MASTER 0x1 /* Waiting to become a master kgdb cpu */
+#define DCPU_NEXT_MASTER 0x2 /* Transition from one master cpu to another */
+#define DCPU_IS_SLAVE    0x4 /* Slave cpu enter exception */
+#define DCPU_SSTEP       0x8 /* CPU is single stepping */
+
 static struct debuggerinfo_struct {
        void                    *debuggerinfo;
        struct task_struct      *task;
+       int                     exception_state;
 } kgdb_info[NR_CPUS];
 
 /**
@@ -558,49 +565,6 @@ static struct task_struct *getthread(struct pt_regs *regs, int tid)
 }
 
 /*
- * CPU debug state control:
- */
-
-#ifdef CONFIG_SMP
-static void kgdb_wait(struct pt_regs *regs)
-{
-       unsigned long flags;
-       int cpu;
-
-       local_irq_save(flags);
-       cpu = raw_smp_processor_id();
-       kgdb_info[cpu].debuggerinfo = regs;
-       kgdb_info[cpu].task = current;
-       /*
-        * Make sure the above info reaches the primary CPU before
-        * our cpu_in_kgdb[] flag setting does:
-        */
-       smp_wmb();
-       atomic_set(&cpu_in_kgdb[cpu], 1);
-
-       /* Disable any cpu specific hw breakpoints */
-       kgdb_disable_hw_debug(regs);
-
-       /* Wait till primary CPU is done with debugging */
-       while (atomic_read(&passive_cpu_wait[cpu]))
-               cpu_relax();
-
-       kgdb_info[cpu].debuggerinfo = NULL;
-       kgdb_info[cpu].task = NULL;
-
-       /* fix up hardware debug registers on local cpu */
-       if (arch_kgdb_ops.correct_hw_break)
-               arch_kgdb_ops.correct_hw_break();
-
-       /* Signal the primary CPU that we are done: */
-       atomic_set(&cpu_in_kgdb[cpu], 0);
-       touch_softlockup_watchdog_sync();
-       clocksource_touch_watchdog();
-       local_irq_restore(flags);
-}
-#endif
-
-/*
  * Some architectures need cache flushes when we set/clear a
  * breakpoint:
  */
@@ -1395,34 +1359,12 @@ static int kgdb_reenter_check(struct kgdb_state *ks)
        return 1;
 }
 
-/*
- * kgdb_handle_exception() - main entry point from a kernel exception
- *
- * Locking hierarchy:
- *     interface locks, if any (begin_session)
- *     kgdb lock (kgdb_active)
- */
-int
-kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
+static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs)
 {
-       struct kgdb_state kgdb_var;
-       struct kgdb_state *ks = &kgdb_var;
        unsigned long flags;
        int sstep_tries = 100;
        int error = 0;
        int i, cpu;
-
-       ks->cpu                 = raw_smp_processor_id();
-       ks->ex_vector           = evector;
-       ks->signo               = signo;
-       ks->ex_vector           = evector;
-       ks->err_code            = ecode;
-       ks->kgdb_usethreadid    = 0;
-       ks->linux_regs          = regs;
-
-       if (kgdb_reenter_check(ks))
-               return 0; /* Ouch, double exception ! */
-
 acquirelock:
        /*
         * Interrupts will be restored by the 'trap return' code, except when
@@ -1430,13 +1372,42 @@ acquirelock:
         */
        local_irq_save(flags);
 
-       cpu = raw_smp_processor_id();
+       cpu = ks->cpu;
+       kgdb_info[cpu].debuggerinfo = regs;
+       kgdb_info[cpu].task = current;
+       /*
+        * Make sure the above info reaches the primary CPU before
+        * our cpu_in_kgdb[] flag setting does:
+        */
+       smp_wmb();
+       atomic_set(&cpu_in_kgdb[cpu], 1);
 
        /*
-        * Acquire the kgdb_active lock:
+        * CPU will loop if it is a slave or request to become a kgdb
+        * master cpu and acquire the kgdb_active lock:
         */
-       while (atomic_cmpxchg(&kgdb_active, -1, cpu) != -1)
+       while (1) {
+               if (kgdb_info[cpu].exception_state & DCPU_WANT_MASTER) {
+                       if (atomic_cmpxchg(&kgdb_active, -1, cpu) == cpu)
+                               break;
+               } else if (kgdb_info[cpu].exception_state & DCPU_IS_SLAVE) {
+                       if (!atomic_read(&passive_cpu_wait[cpu]))
+                               goto return_normal;
+               } else {
+return_normal:
+                       /* Return to normal operation by executing any
+                        * hw breakpoint fixup.
+                        */
+                       if (arch_kgdb_ops.correct_hw_break)
+                               arch_kgdb_ops.correct_hw_break();
+                       atomic_set(&cpu_in_kgdb[cpu], 0);
+                       touch_softlockup_watchdog_sync();
+                       clocksource_touch_watchdog();
+                       local_irq_restore(flags);
+                       return 0;
+               }
                cpu_relax();
+       }
 
        /*
         * For single stepping, try to only enter on the processor
@@ -1470,9 +1441,6 @@ acquirelock:
        if (kgdb_io_ops->pre_exception)
                kgdb_io_ops->pre_exception();
 
-       kgdb_info[ks->cpu].debuggerinfo = ks->linux_regs;
-       kgdb_info[ks->cpu].task = current;
-
        kgdb_disable_hw_debug(ks->linux_regs);
 
        /*
@@ -1484,12 +1452,6 @@ acquirelock:
                        atomic_set(&passive_cpu_wait[i], 1);
        }
 
-       /*
-        * spin_lock code is good enough as a barrier so we don't
-        * need one here:
-        */
-       atomic_set(&cpu_in_kgdb[ks->cpu], 1);
-
 #ifdef CONFIG_SMP
        /* Signal the other CPUs to enter kgdb_wait() */
        if ((!kgdb_single_step) && kgdb_do_roundup)
@@ -1521,8 +1483,6 @@ acquirelock:
        if (kgdb_io_ops->post_exception)
                kgdb_io_ops->post_exception();
 
-       kgdb_info[ks->cpu].debuggerinfo = NULL;
-       kgdb_info[ks->cpu].task = NULL;
        atomic_set(&cpu_in_kgdb[ks->cpu], 0);
 
        if (!kgdb_single_step) {
@@ -1555,13 +1515,52 @@ kgdb_restore:
        return error;
 }
 
+/*
+ * kgdb_handle_exception() - main entry point from a kernel exception
+ *
+ * Locking hierarchy:
+ *     interface locks, if any (begin_session)
+ *     kgdb lock (kgdb_active)
+ */
+int
+kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
+{
+       struct kgdb_state kgdb_var;
+       struct kgdb_state *ks = &kgdb_var;
+       int ret;
+
+       ks->cpu                 = raw_smp_processor_id();
+       ks->ex_vector           = evector;
+       ks->signo               = signo;
+       ks->ex_vector           = evector;
+       ks->err_code            = ecode;
+       ks->kgdb_usethreadid    = 0;
+       ks->linux_regs          = regs;
+
+       if (kgdb_reenter_check(ks))
+               return 0; /* Ouch, double exception ! */
+       kgdb_info[ks->cpu].exception_state |= DCPU_WANT_MASTER;
+       ret = kgdb_cpu_enter(ks, regs);
+       kgdb_info[ks->cpu].exception_state &= ~DCPU_WANT_MASTER;
+       return ret;
+}
+
 int kgdb_nmicallback(int cpu, void *regs)
 {
 #ifdef CONFIG_SMP
+       struct kgdb_state kgdb_var;
+       struct kgdb_state *ks = &kgdb_var;
+
+       memset(ks, 0, sizeof(struct kgdb_state));
+       ks->cpu                 = cpu;
+       ks->linux_regs          = regs;
+
        if (!atomic_read(&cpu_in_kgdb[cpu]) &&
-                       atomic_read(&kgdb_active) != cpu &&
-                       atomic_read(&cpu_in_kgdb[atomic_read(&kgdb_active)])) {
-               kgdb_wait((struct pt_regs *)regs);
+           atomic_read(&kgdb_active) != -1 &&
+           atomic_read(&kgdb_active) != cpu) {
+               kgdb_info[cpu].exception_state |= DCPU_IS_SLAVE;
+               kgdb_cpu_enter(ks, regs);
+               kgdb_info[cpu].exception_state &= ~DCPU_IS_SLAVE;
                return 0;
        }
 #endif