powerpc: Fix usage of elision transient failure adapt param

The skip_lock_out_of_tbegin_retries adaptive parameter was
not being used correctly, nor as described.  This prevents
a fallback for all users of the lock if a transient abort
occurs within the accepted number of retries.

	[BZ #19174]
	* sysdeps/powerpc/nptl/elide.h (__elide_lock): Fix usage of
	.skip_lock_out_of_tbegin_retries.
	* sysdeps/unix/sysv/linux/powerpc/elision-lock.c
	(__lll_lock_elision): Likewise, and respect a value of
	try_tbegin <= 0.

(cherry picked from commit 72f1463df85a522bfd1568e47bd81371522ee358)

Conflicts:
	NEWS

diff --git a/ChangeLog b/ChangeLog
index 5c92a3e8c644540692107cdfd9e4fa8a1330170b..d96d6efec21b50c5bc100a35bd7e02861c45411b 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+2015-12-17  Paul E. Murphy  <murphyp@linux.vnet.ibm.com>
+
+       [BZ #19174]
+       * sysdeps/powerpc/nptl/elide.h (__elide_lock): Fix usage of
+       .skip_lock_out_of_tbegin_retries.
+       * sysdeps/unix/sysv/linux/powerpc/elision-lock.c
+       (__lll_lock_elision): Likewise, and respect a value of
+       try_tbegin <= 0.
+
 2015-12-03  Andrew Senkevich  <andrew.senkevich@intel.com>
 
        * math/Makefile ($(inst_libdir)/libm.so): Corrected path to

diff --git a/NEWS b/NEWS
index e1003189f6384fe368a9c65866ec090741f53782..e1c1e58271d84604386f8a131a1bde4816f3454d 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -10,7 +10,7 @@ Version 2.22.1
 * The following bugs are resolved with this release:
 
   18589, 18743, 18778, 18781, 18787, 18796, 18870, 18887, 18921, 18928,
-  18969, 19018, 19058, 19178.
+  18969, 19018, 19058, 19174, 19178.
 
 * The LD_POINTER_GUARD environment variable can no longer be used to
   disable the pointer guard feature.  It is always enabled.

diff --git a/sysdeps/powerpc/nptl/elide.h b/sysdeps/powerpc/nptl/elide.h
index 12171f45dc1758f5d9a4f5ae07d57516fae53459..2e1e4432789ef858be07d63391dc247a202f2577 100644 (file)
--- a/sysdeps/powerpc/nptl/elide.h
+++ b/sysdeps/powerpc/nptl/elide.h
@@ -27,7 +27,7 @@
    configurations.  Returns true if the system should retry again or false
    otherwise.  */
 static inline bool
-__get_new_count (uint8_t *adapt_count)
+__get_new_count (uint8_t *adapt_count, int attempt)
 {
   /* A persistent failure indicates that a retry will probably
      result in another failure.  Use normal locking now and
@@ -40,7 +40,7 @@ __get_new_count (uint8_t *adapt_count)
     }
   /* Same logic as above, but for a number of temporary failures in a
      a row.  */
-  else if (__elision_aconf.skip_lock_out_of_tbegin_retries > 0
+  else if (attempt <= 1 && __elision_aconf.skip_lock_out_of_tbegin_retries > 0
           && __elision_aconf.try_tbegin > 0)
     *adapt_count = __elision_aconf.skip_lock_out_of_tbegin_retries;
   return true;
@@ -78,7 +78,7 @@ __get_new_count (uint8_t *adapt_count)
              __builtin_tabort (_ABORT_LOCK_BUSY);                      \
            }                                                           \
          else                                                          \
-           if (!__get_new_count(&adapt_count))                         \
+           if (!__get_new_count (&adapt_count,i))                      \
              break;                                                    \
        }                                                               \
     ret;                                                               \

diff --git a/sysdeps/unix/sysv/linux/powerpc/elision-lock.c b/sysdeps/unix/sysv/linux/powerpc/elision-lock.c
index 7f9bcc2bf1ee4b40d4a77583ba1ae3d7824e7800..c6731ca6a4b07bf567c624d285a89e4a2692377e 100644 (file)
--- a/sysdeps/unix/sysv/linux/powerpc/elision-lock.c
+++ b/sysdeps/unix/sysv/linux/powerpc/elision-lock.c
@@ -72,8 +72,7 @@ __lll_lock_elision (int *lock, short *adapt_count, EXTRAARG int pshared)
       goto use_lock;
     }
 
-  int try_begin = aconf.try_tbegin;
-  while (1)
+  for (int i = aconf.try_tbegin; i > 0; i--)
     {
       if (__builtin_tbegin (0))
        {
@@ -87,21 +86,19 @@ __lll_lock_elision (int *lock, short *adapt_count, EXTRAARG int pshared)
          /* A persistent failure indicates that a retry will probably
             result in another failure.  Use normal locking now and
             for the next couple of calls.  */
-         if (try_begin-- <= 0
-             || _TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ()))
+         if (_TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ()))
            {
              if (aconf.skip_lock_internal_abort > 0)
                *adapt_count = aconf.skip_lock_internal_abort;
              goto use_lock;
            }
-         /* Same logic as above, but for for a number of temporary failures
-            in a row.  */
-         else if (aconf.skip_lock_out_of_tbegin_retries > 0
-                   && aconf.try_tbegin > 0)
-           *adapt_count = aconf.skip_lock_out_of_tbegin_retries;
        }
      }
 
+  /* Fall back to locks for a bit if retries have been exhausted */
+  if (aconf.try_tbegin > 0 && aconf.skip_lock_out_of_tbegin_retries > 0)
+    *adapt_count = aconf.skip_lock_out_of_tbegin_retries;
+
 use_lock:
   return LLL_LOCK ((*lock), pshared);
 }