2 files changed, 13 insertions, 18 deletions

diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index 46f477bebe0c..daa76154fb1b 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -555,16 +555,16 @@ int vkdb_printf(enum kdb_msgsrc src, const char *fmt, va_list ap)
         int colcount;
         int logging, saved_loglevel = 0;
         int saved_trap_printk;
-        int got_printf_lock = 0;
         int retlen = 0;
         int fnd, len;
+        int this_cpu, old_cpu;
+        static int kdb_printf_cpu = -1;
         char *cp, *cp2, *cphold = NULL, replaced_byte = ' ';
         char *moreprompt = "more> ";
         struct console *c = console_drivers;
-        static DEFINE_SPINLOCK(kdb_printf_lock);
         unsigned long uninitialized_var(flags);
 
-        preempt_disable();
+        local_irq_save(flags);
         saved_trap_printk = kdb_trap_printk;
         kdb_trap_printk = 0;
 
@@ -572,12 +572,13 @@ int vkdb_printf(enum kdb_msgsrc src, const char *fmt, va_list ap)
          * But if any cpu goes recursive in kdb, just print the output,
          * even if it is interleaved with any other text.
          */
-        if (!KDB_STATE(PRINTF_LOCK)) {
-                KDB_STATE_SET(PRINTF_LOCK);
-                spin_lock_irqsave(&kdb_printf_lock, flags);
-                got_printf_lock = 1;
-        } else {
-                __acquire(kdb_printf_lock);
+        this_cpu = smp_processor_id();
+        for (;;) {
+                old_cpu = cmpxchg(&kdb_printf_cpu, -1, this_cpu);
+                if (old_cpu == -1 || old_cpu == this_cpu)
+                        break;
+
+                cpu_relax();
         }
 
         diag = kdbgetintenv("LINES", &linecount);
@@ -846,15 +847,10 @@ kdb_print_out:
         suspend_grep = 0; /* end of what may have been a recursive call */
         if (logging)
                 console_loglevel = saved_loglevel;
-        if (KDB_STATE(PRINTF_LOCK) && got_printf_lock) {
-                got_printf_lock = 0;
-                spin_unlock_irqrestore(&kdb_printf_lock, flags);
-                KDB_STATE_CLEAR(PRINTF_LOCK);
-        } else {
-                __release(kdb_printf_lock);
-        }
+        /* kdb_printf_cpu locked the code above. */
+        smp_store_release(&kdb_printf_cpu, old_cpu);
         kdb_trap_printk = saved_trap_printk;
-        preempt_enable();
+        local_irq_restore(flags);
         return retlen;
 }
 
diff --git a/kernel/debug/kdb/kdb_private.h b/kernel/debug/kdb/kdb_private.h
index 75014d7f4568..fc224fbcf954 100644
--- a/kernel/debug/kdb/kdb_private.h
+++ b/kernel/debug/kdb/kdb_private.h
@@ -132,7 +132,6 @@ extern int kdb_state;
 #define KDB_STATE_PAGER         0x00000400      /* pager is available */
 #define KDB_STATE_GO_SWITCH     0x00000800      /* go is switching
                                                  * back to initial cpu */
-#define KDB_STATE_PRINTF_LOCK   0x00001000      /* Holds kdb_printf lock */
 #define KDB_STATE_WAIT_IPI      0x00002000      /* Waiting for kdb_ipi() NMI */
 #define KDB_STATE_RECURSE       0x00004000      /* Recursive entry to kdb */
 #define KDB_STATE_IP_ADJUSTED   0x00008000      /* Restart IP has been