TRACE(): facilitate debugging

- don't deadlock on a runqueue lock in case of a bug inside
  the scheduler
- write printk() messages to TRACE()
- tell user of TRACE() buffer

2 files changed, 39 insertions, 3 deletions

diff --git a/kernel/printk.c b/kernel/printk.c
index 89011bf8c1..9eb2dc5e27 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -54,6 +54,12 @@ int console_printk[4] = {
         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
 };
 
+/* divert printk() messages when we have a LITMUS^RT
+ * debug listener
+ */
+#include <litmus/litmus.h>
+int trace_override = 0;
+
 /*
  * Low level drivers may need that to know if they can schedule in
  * their unblank() callback or not. So let's export it.
@@ -652,6 +658,8 @@ asmlinkage int vprintk(const char *fmt, va_list args)
 
         /* Emit the output into the temporary buffer */
         printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
+        if (trace_override)
+                TRACE("%s", printk_buf);
 
         /*
          * Copy the output into log_buf.  If the caller didn't provide
@@ -932,7 +940,7 @@ int is_console_locked(void)
 
 void wake_up_klogd(void)
 {
-        if (!oops_in_progress && waitqueue_active(&log_wait))
+        if (!trace_override && !oops_in_progress && waitqueue_active(&log_wait))
                 wake_up_interruptible(&log_wait);
 }
 
diff --git a/litmus/sched_trace.c b/litmus/sched_trace.c
index 0976e830ad..43447851da 100644
--- a/litmus/sched_trace.c
+++ b/litmus/sched_trace.c
@@ -373,6 +373,9 @@ static int trace_open(struct inode *in, struct file *filp)
         return error;
 }
 
+
+extern int trace_override;
+
 /* log_open - open the global log message ring buffer.
  */
 static int log_open(struct inode *in, struct file *filp)
@@ -398,13 +401,38 @@ static int log_open(struct inode *in, struct file *filp)
 
         error = 0;
         filp->private_data = buf;
-
+        printk(KERN_DEBUG "sched_trace buf: from 0x%p to 0x%p  length: %lx\n",
+               buf->buf.buf, buf->buf.end, buf->buf.end - buf->buf.buf);
+        trace_override++;
  out_unlock:
         up(&buf->reader_mutex);
  out:
         return error;
 }
 
+static int log_release(struct inode *in, struct file *filp)
+{
+        int error               = -EINVAL;
+        trace_buffer_t* buf     = filp->private_data;
+
+        BUG_ON(!filp->private_data);
+
+        if (down_interruptible(&buf->reader_mutex)) {
+                error = -ERESTARTSYS;
+                goto out;
+        }
+
+        /*      last release must deallocate buffers    */
+        if (atomic_dec_return(&buf->reader_cnt) == 0) {
+                error = rb_free_buf(&buf->buf);
+        }
+
+        trace_override--;
+        up(&buf->reader_mutex);
+ out:
+        return error;
+}
+
 /******************************************************************************/
 /*                          Device Registration                               */
 /******************************************************************************/
@@ -434,7 +462,7 @@ struct file_operations trace_fops = {
 struct file_operations log_fops = {
         .owner   = THIS_MODULE,
         .open    = log_open,
-        .release = trace_release,
+        .release = log_release,
         .read    = trace_read,
 };