relay-writer-lock.diff

diff --git a/runtime/print_flush.c b/runtime/print_flush.c
index 18b3e8f62..a0fa71b48 100644
--- a/runtime/print_flush.c
+++ b/runtime/print_flush.c
@@ -111,6 +111,13 @@ void stp_print_flush(_stp_pbuf *pb)
                struct context* __restrict__ c = NULL;
                char *bufp = pb->buf;

+#if defined(__KERNEL__)
+               int locked;
+               struct rchan_buf *buf;
+               struct inode *inode;
+               int i;
+#endif
+
                /* Prevent probe reentrancy on _stp_print_lock.
                 *
                 * Since stp_print_flush may be called from probe context, we
@@ -131,6 +138,25 @@ void stp_print_flush(_stp_pbuf *pb)

                dbug_trans(1, "calling _stp_data_write...\n");
                stp_spin_lock_irqsave(&_stp_print_lock, flags);
+
+#if defined(__KERNEL__)
+               buf = _stp_get_rchan_subbuf(_stp_relay_data.rchan->buf,
+                                           smp_processor_id());
+
+               inode = buf->dentry->d_inode;
+
+               /* emulate a spin lock here */
+               for (i = 0; i < 200; i++) {
+                       locked = down_write_trylock(&inode->i_rwsem);
+                       if (locked)
+                               break;
+               }
+
+#ifdef DEBUG_TRANS
+               if (!locked)
+                       dbug_trans(0, "failed to lock the relay file inode");
+#endif
+#endif  /* defined(__KERNEL__) */
+
                while (len > 0) {
                        size_t bytes_reserved;

@@ -147,6 +173,12 @@ void stp_print_flush(_stp_pbuf *pb)
                            break;
                        }
                }
+
+#if defined(__KERNEL__)
+               if (locked)
+                       up_write(&inode->i_rwsem);
+#endif
+
                stp_spin_unlock_irqrestore(&_stp_print_lock, flags);
                _stp_runtime_entryfn_put_context(c);
        }