Bug#13898343 THREAD LOOPS ENDLESSLY IN LF_PINBOX_PUT_PINS WHILE HOLDING

LOCK_THREAD_COUNT

When using the performance schema file io instrumentation in MySQL 5.5,
a thread would loop forever inside lf_pinbox_put_pins, when disconnecting.
It would also hold LOCK_thread_count while doing so, effectively killing the
server.

The root cause of the loop in lf_pinbox_put_pins() is a leak of LF_PINS,
when used with the filename_hash LF_HASH table in the performance schema.

This fix contains the following changes:

1)
Added the missing call to lf_hash_search_unpin(), to prevent the leak.

2)
In mysys/lf_alloc-pin.c, there was some extra debugging code
(MY_LF_EXTRA_DEBUG) written to detect precisely this kind of issues,
but it was never used.
Replaced MY_LF_EXTRA_DEBUG with DBUG_OFF, so that leaks similar to this one
can be always detected in regular debug builds.

3)
Backported the fix for the following bug, from 5.6 to 5.5:
Bug#13417446 - 63339: INCORRECT FILE PATH IN PEFORMANCE_SCHEMA ON WINDOWS

mysys/lf_alloc-pin.c

@@ -211,13 +211,16 @@ void _lf_pinbox_put_pins(LF_PINS *pins)
   LF_PINBOX *pinbox= pins->pinbox;
   uint32 top_ver, nr;
   nr= pins->link;
-#ifdef MY_LF_EXTRA_DEBUG
+
+#ifndef DBUG_OFF
   {
+    /* This thread should not hold any pin. */
     int i;
     for (i= 0; i < LF_PINBOX_PINS; i++)
       DBUG_ASSERT(pins->pin[i] == 0);
   }
-#endif
+#endif /* DBUG_OFF */
+
   /*
     XXX this will deadlock if other threads will wait for
     the caller to do something after _lf_pinbox_put_pins(),

storage/perfschema/pfs_instr.cc

-/* Copyright (c) 2008, 2010, Oracle and/or its affiliates. All rights reserved.
+/* Copyright (c) 2008, 2012, Oracle and/or its affiliates. All rights reserved.
 
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
@@ -801,6 +801,22 @@ void destroy_thread(PFS_thread *pfs)
   pfs->m_lock.allocated_to_free();
 }
 
+/**
+  Get the hash pins for @filename_hash.
+  @param thread The running thread.
+  @returns The LF_HASH pins for the thread.
+*/
+LF_PINS* get_filename_hash_pins(PFS_thread *thread)
+{
+  if (unlikely(thread->m_filename_hash_pins == NULL))
+  {
+    if (! filename_hash_inited)
+      return NULL;
+    thread->m_filename_hash_pins= lf_hash_get_pins(&filename_hash);
+  }
+  return thread->m_filename_hash_pins;
+}
+
 /**
   Find or create instrumentation for a file instance by file name.
   @param thread                       the executing instrumented thread
@@ -816,22 +832,12 @@ find_or_create_file(PFS_thread *thread, PFS_file_class *klass,
   PFS_file *pfs;
   PFS_scan scan;
 
-  if (! filename_hash_inited)
-  {
-    /* File instrumentation can be turned off. */
-    file_lost++;
-    return NULL;
-  }
-
-  if (unlikely(thread->m_filename_hash_pins == NULL))
-  {
-    thread->m_filename_hash_pins= lf_hash_get_pins(&filename_hash);
-    if (unlikely(thread->m_filename_hash_pins == NULL))
+  LF_PINS *pins= get_filename_hash_pins(thread);
+  if (unlikely(pins == NULL))
   {
     file_lost++;
     return NULL;
   }
-  }
 
   char safe_buffer[FN_REFLEN];
   const char *safe_filename;
@@ -904,7 +910,7 @@ find_or_create_file(PFS_thread *thread, PFS_file_class *klass,
   /* Append the unresolved file name to the resolved path */
   char *ptr= buffer + strlen(buffer);
   char *buf_end= &buffer[sizeof(buffer)-1];
-  if (buf_end > ptr)
+  if ((buf_end > ptr) && (*(ptr-1) != FN_LIBCHAR))
     *ptr++= FN_LIBCHAR;
   if (buf_end > ptr)
     strncpy(ptr, safe_filename + dirlen, buf_end - ptr);
@@ -918,16 +924,18 @@ find_or_create_file(PFS_thread *thread, PFS_file_class *klass,
   const uint retry_max= 3;
 search:
   entry= reinterpret_cast<PFS_file**>
-    (lf_hash_search(&filename_hash, thread->m_filename_hash_pins,
+    (lf_hash_search(&filename_hash, pins,
                     normalized_filename, normalized_length));
   if (entry && (entry != MY_ERRPTR))
   {
     pfs= *entry;
     pfs->m_file_stat.m_open_count++;
-    lf_hash_search_unpin(thread->m_filename_hash_pins);
+    lf_hash_search_unpin(pins);
     return pfs;
   }
 
+  lf_hash_search_unpin(pins);
+
   /* filename is not constant, just using it for noise on create */
   uint random= randomized_index(filename, file_max);
 
@@ -954,7 +962,7 @@ search:
           reset_single_stat_link(&pfs->m_wait_stat);
 
           int res;
-          res= lf_hash_insert(&filename_hash, thread->m_filename_hash_pins,
+          res= lf_hash_insert(&filename_hash, pins,
                               &pfs);
           if (likely(res == 0))
           {
@@ -1006,9 +1014,12 @@ void release_file(PFS_file *pfs)
 void destroy_file(PFS_thread *thread, PFS_file *pfs)
 {
   DBUG_ASSERT(thread != NULL);
-  DBUG_ASSERT(thread->m_filename_hash_pins != NULL);
   DBUG_ASSERT(pfs != NULL);
-  lf_hash_delete(&filename_hash, thread->m_filename_hash_pins,
+
+  LF_PINS *pins= get_filename_hash_pins(thread);
+  DBUG_ASSERT(pins != NULL);
+
+  lf_hash_delete(&filename_hash, pins,
                  pfs->m_filename, pfs->m_filename_length);
   pfs->m_lock.allocated_to_free();
 }