This is the mail archive of the libc-alpha@sourceware.org mailing list for the glibc project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

[PATCH][BZ 18743] PowerPC: Fix a race condition when eliding a lock


Note: this patch is updating the NEWS section of glibc 2.22 because that's the
only one available right now.  Whether this patch will end up in glibc 2.23
or 2.22 has to be defined.

8<----

The previous code used to evaluate the preprocessor token is_lock_free to
a variable before starting a transaction.  This behavior can cause an
error if another thread got the lock (without using a transaction)
between the conversion of the token and the beginning of the transaction.

This patch delays the evaluation of is_lock_free to inside a transaction
by moving this part of the code to the macro ELIDE_LOCK.

2015-07-30  Tulio Magno Quites Machado Filho  <tuliom@linux.vnet.ibm.com>

	[BZ #18743]
	* sysdeps/powerpc/nptl/elide.h (__elide_lock): Move most of this
	code to...
	(ELIDE_LOCK): ...here.
	(__get_new_count): New function with part of the code from
	__elide_lock that updates the value of adapt_count after a
	transaction abort.
	(__elided_trylock): Moved this code to...
	(ELIDE_TRYLOCK): ...here.
---
 NEWS                         |   2 +-
 sysdeps/powerpc/nptl/elide.h | 104 +++++++++++++++++++++----------------------
 2 files changed, 53 insertions(+), 53 deletions(-)

diff --git a/NEWS b/NEWS
index 5698310..92996d5 100644
--- a/NEWS
+++ b/NEWS
@@ -28,7 +28,7 @@ Version 2.22
   18536, 18539, 18540, 18542, 18544, 18545, 18546, 18547, 18549, 18553,
   18557, 18558, 18569, 18583, 18585, 18586, 18592, 18593, 18594, 18602,
   18612, 18613, 18619, 18633, 18641, 18643, 18648, 18657, 18676, 18694,
-  18696.
+  18696, 18743.
 
 * Cache information can be queried via sysconf() function on s390 e.g. with
   _SC_LEVEL1_ICACHE_SIZE as argument.
diff --git a/sysdeps/powerpc/nptl/elide.h b/sysdeps/powerpc/nptl/elide.h
index 389f5a5..1d04ee9 100644
--- a/sysdeps/powerpc/nptl/elide.h
+++ b/sysdeps/powerpc/nptl/elide.h
@@ -23,67 +23,67 @@
 # include <htm.h>
 # include <elision-conf.h>
 
-/* Returns true if the lock defined by is_lock_free as elided.
-   ADAPT_COUNT is a pointer to per-lock state variable. */
-
+/* Get the new value of adapt_count according to the elision
+   configurations.  Returns true if the system should retry again or false
+   otherwise.  */
 static inline bool
-__elide_lock (uint8_t *adapt_count, int is_lock_free)
+__get_new_count (uint8_t *adapt_count)
 {
-  if (*adapt_count > 0)
+  /* 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 (_TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ()))
     {
-      (*adapt_count)--;
+      if (__elision_aconf.skip_lock_internal_abort > 0)
+	*adapt_count = __elision_aconf.skip_lock_internal_abort;
       return false;
     }
-
-  for (int i = __elision_aconf.try_tbegin; i > 0; i--)
-    {
-      if (__builtin_tbegin (0))
-	{
-	  if (is_lock_free)
-	    return true;
-	  /* Lock was busy.  */
-	  __builtin_tabort (_ABORT_LOCK_BUSY);
-	}
-      else
-	{
-	  /* 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 (_TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ()))
-	    {
-	      if (__elision_aconf.skip_lock_internal_abort > 0)
-		*adapt_count = __elision_aconf.skip_lock_internal_abort;
-	      break;
-	    }
-	  /* 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
-		   && __elision_aconf.try_tbegin > 0)
-	    *adapt_count = __elision_aconf.skip_lock_out_of_tbegin_retries;
-	}
-     }
-
-  return false;
+  /* 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
+	   && __elision_aconf.try_tbegin > 0)
+    *adapt_count = __elision_aconf.skip_lock_out_of_tbegin_retries;
+  return true;
 }
 
-# define ELIDE_LOCK(adapt_count, is_lock_free) \
-  __elide_lock (&(adapt_count), is_lock_free)
-
-
-static inline bool
-__elide_trylock (uint8_t *adapt_count, int is_lock_free, int write)
-{
-  if (__elision_aconf.try_tbegin > 0)
-    {
-      if (write)
-	__builtin_tabort (_ABORT_NESTED_TRYLOCK);
-      return __elide_lock (adapt_count, is_lock_free);
-    }
-  return false;
-}
+/* Returns 0 if the lock defined by is_lock_free was elided.
+   ADAPT_COUNT is a per-lock state variable.  */
+# define ELIDE_LOCK(adapt_count, is_lock_free)				\
+  ({									\
+    int ret = 0;							\
+    if (adapt_count > 0)						\
+      (adapt_count)--;							\
+    else								\
+      for (int i = __elision_aconf.try_tbegin; i > 0; i--)		\
+	{								\
+	  asm volatile("" ::: "memory");				\
+	  if (__builtin_tbegin (0))					\
+	    {								\
+	      if (is_lock_free)						\
+		{							\
+		  ret = 1;						\
+		  break;						\
+		}							\
+	      __builtin_tabort (_ABORT_LOCK_BUSY);			\
+	    }								\
+	  else								\
+	    if (!__get_new_count(&adapt_count))				\
+	      break;							\
+	}								\
+    ret;								\
+  })
 
 # define ELIDE_TRYLOCK(adapt_count, is_lock_free, write)	\
-  __elide_trylock (&(adapt_count), is_lock_free, write)
+  ({								\
+    int ret = 0;						\
+    if (__elision_aconf.try_tbegin > 0)				\
+      {								\
+	if (write)						\
+	  __builtin_tabort (_ABORT_NESTED_TRYLOCK);		\
+	ret = ELIDE_LOCK (adapt_count, is_lock_free);		\
+      }								\
+    ret;							\
+  })
 
 
 static inline bool
-- 
2.1.0


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]