nptl: Move cancel type out of cancelhandling

Now that the thread cancellation type is not accessed concurrently
anymore, it is possible to move it out the cancelhandling.

By removing the cancel state out of the internal thread cancel handling
state there is no need to check if cancelled bit was set in CAS
operation.

It allows simplifing the cancellation wrappers and the
CANCEL_CANCELED_AND_ASYNCHRONOUS is removed.

Checked on x86_64-linux-gnu and aarch64-linux-gnu.

8 files changed, 35 insertions, 170 deletions

diff --git a/nptl/allocatestack.c b/nptl/allocatestack.c
index 54e95ba..9be6c42 100644
--- a/nptl/allocatestack.c
+++ b/nptl/allocatestack.c
@@ -161,6 +161,7 @@ get_cached_stack (size_t *sizep, void **memp)
   /* Cancellation handling is back to the default.  */
   result->cancelhandling = 0;
   result->cancelstate = PTHREAD_CANCEL_ENABLE;
+  result->canceltype = PTHREAD_CANCEL_DEFERRED;
   result->cleanup = NULL;
   result->setup_failed = 0;
 
diff --git a/nptl/cancellation.c b/nptl/cancellation.c
index ce00603..0596278 100644
--- a/nptl/cancellation.c
+++ b/nptl/cancellation.c
@@ -31,31 +31,19 @@ int
 __pthread_enable_asynccancel (void)
 {
   struct pthread *self = THREAD_SELF;
-  int oldval = THREAD_GETMEM (self, cancelhandling);
 
-  while (1)
-    {
-      int newval = oldval | CANCELTYPE_BITMASK;
-
-      if (newval == oldval)
-	break;
-
-      int curval = THREAD_ATOMIC_CMPXCHG_VAL (self, cancelhandling, newval,
-					      oldval);
-      if (__glibc_likely (curval == oldval))
-	{
-	  if (self->cancelstate == PTHREAD_CANCEL_ENABLE
-	      && CANCEL_CANCELED_AND_ASYNCHRONOUS (newval))
-	    {
-	      THREAD_SETMEM (self, result, PTHREAD_CANCELED);
-	      __do_cancel ();
-	    }
+  int oldval = THREAD_GETMEM (self, canceltype);
+  THREAD_SETMEM (self, canceltype, PTHREAD_CANCEL_ASYNCHRONOUS);
 
-	  break;
-	}
+  int ch = THREAD_GETMEM (self, cancelhandling);
 
-      /* Prepare the next round.  */
-      oldval = curval;
+  if (self->cancelstate == PTHREAD_CANCEL_ENABLE
+      && (ch & CANCELED_BITMASK)
+      && !(ch & EXITING_BITMASK)
+      && !(ch & TERMINATED_BITMASK))
+    {
+      THREAD_SETMEM (self, result, PTHREAD_CANCELED);
+      __do_cancel ();
     }
 
   return oldval;
@@ -69,25 +57,10 @@ __pthread_disable_asynccancel (int oldtype)
 {
   /* If asynchronous cancellation was enabled before we do not have
      anything to do.  */
-  if (oldtype & CANCELTYPE_BITMASK)
+  if (oldtype == PTHREAD_CANCEL_ASYNCHRONOUS)
     return;
 
   struct pthread *self = THREAD_SELF;
-  int newval;
-
-  int oldval = THREAD_GETMEM (self, cancelhandling);
-
-  while (1)
-    {
-      newval = oldval & ~CANCELTYPE_BITMASK;
-
-      int curval = THREAD_ATOMIC_CMPXCHG_VAL (self, cancelhandling, newval,
-					      oldval);
-      if (__glibc_likely (curval == oldval))
-	break;
-
-      /* Prepare the next round.  */
-      oldval = curval;
-    }
+  self->canceltype = PTHREAD_CANCEL_DEFERRED;
 }
 libc_hidden_def (__pthread_disable_asynccancel)
diff --git a/nptl/cleanup_defer.c b/nptl/cleanup_defer.c
index 873ab00..7e858d0 100644
--- a/nptl/cleanup_defer.c
+++ b/nptl/cleanup_defer.c
@@ -31,27 +31,9 @@ ___pthread_register_cancel_defer (__pthread_unwind_buf_t *buf)
   ibuf->priv.data.prev = THREAD_GETMEM (self, cleanup_jmp_buf);
   ibuf->priv.data.cleanup = THREAD_GETMEM (self, cleanup);
 
-  int cancelhandling = THREAD_GETMEM (self, cancelhandling);
-
   /* Disable asynchronous cancellation for now.  */
-  if (__glibc_unlikely (cancelhandling & CANCELTYPE_BITMASK))
-    while (1)
-      {
-	int curval = THREAD_ATOMIC_CMPXCHG_VAL (self, cancelhandling,
-						cancelhandling
-						& ~CANCELTYPE_BITMASK,
-						cancelhandling);
-	if (__glibc_likely (curval == cancelhandling))
-	  /* Successfully replaced the value.  */
-	  break;
-
-	/* Prepare for the next round.  */
-	cancelhandling = curval;
-      }
-
-  ibuf->priv.data.canceltype = (cancelhandling & CANCELTYPE_BITMASK
-				? PTHREAD_CANCEL_ASYNCHRONOUS
-				: PTHREAD_CANCEL_DEFERRED);
+  ibuf->priv.data.canceltype = THREAD_GETMEM (self, canceltype);
+  THREAD_SETMEM (self, canceltype, PTHREAD_CANCEL_DEFERRED);
 
   /* Store the new cleanup handler info.  */
   THREAD_SETMEM (self, cleanup_jmp_buf, (struct pthread_unwind_buf *) buf);
@@ -73,27 +55,9 @@ ___pthread_unregister_cancel_restore (__pthread_unwind_buf_t *buf)
 
   THREAD_SETMEM (self, cleanup_jmp_buf, ibuf->priv.data.prev);
 
-  int cancelhandling;
-  if (ibuf->priv.data.canceltype != PTHREAD_CANCEL_DEFERRED
-      && ((cancelhandling = THREAD_GETMEM (self, cancelhandling))
-	  & CANCELTYPE_BITMASK) == 0)
-    {
-      while (1)
-	{
-	  int curval = THREAD_ATOMIC_CMPXCHG_VAL (self, cancelhandling,
-						  cancelhandling
-						  | CANCELTYPE_BITMASK,
-						  cancelhandling);
-	  if (__glibc_likely (curval == cancelhandling))
-	    /* Successfully replaced the value.  */
-	    break;
-
-	  /* Prepare for the next round.  */
-	  cancelhandling = curval;
-	}
-
-      __pthread_testcancel ();
-    }
+  THREAD_SETMEM (self, canceltype, ibuf->priv.data.canceltype);
+  if (ibuf->priv.data.canceltype == PTHREAD_CANCEL_ASYNCHRONOUS)
+    __pthread_testcancel ();
 }
 versioned_symbol (libc, ___pthread_unregister_cancel_restore,
 		  __pthread_unregister_cancel_restore, GLIBC_2_34);
diff --git a/nptl/descr.h b/nptl/descr.h
index 35f5330..c85778d 100644
--- a/nptl/descr.h
+++ b/nptl/descr.h
@@ -277,9 +277,6 @@ struct pthread
 
   /* Flags determining processing of cancellation.  */
   int cancelhandling;
-  /* Bit set if asynchronous cancellation mode is selected.  */
-#define CANCELTYPE_BIT		1
-#define CANCELTYPE_BITMASK	(0x01 << CANCELTYPE_BIT)
   /* Bit set if canceled.  */
 #define CANCELED_BIT		3
 #define CANCELED_BITMASK	(0x01 << CANCELED_BIT)
@@ -292,13 +289,6 @@ struct pthread
   /* Bit set if thread is supposed to change XID.  */
 #define SETXID_BIT		6
 #define SETXID_BITMASK		(0x01 << SETXID_BIT)
-  /* Mask for the rest.  Helps the compiler to optimize.  */
-#define CANCEL_RESTMASK		0xffffff80
-
-#define CANCEL_CANCELED_AND_ASYNCHRONOUS(value) \
-  (((value) & (CANCELTYPE_BITMASK | CANCELED_BITMASK    \
-	       | EXITING_BITMASK | CANCEL_RESTMASK | TERMINATED_BITMASK))     \
-   == (CANCELTYPE_BITMASK | CANCELED_BITMASK))
 
   /* Flags.  Including those copied from the thread attribute.  */
   int flags;
@@ -402,6 +392,10 @@ struct pthread
      PTHREAD_CANCEL_DISABLE).  */
   unsigned char cancelstate;
 
+  /* Thread cancel type (PTHREAD_CANCEL_DEFERRED or
+     PTHREAD_CANCEL_ASYNCHRONOUS).  */
+  unsigned char canceltype;
+
   /* Used on strsignal.  */
   struct tls_internal_t tls_state;
 
diff --git a/nptl/libc-cleanup.c b/nptl/libc-cleanup.c
index 6286b8b..180d15b 100644
--- a/nptl/libc-cleanup.c
+++ b/nptl/libc-cleanup.c
@@ -27,27 +27,9 @@ __libc_cleanup_push_defer (struct _pthread_cleanup_buffer *buffer)
 
   buffer->__prev = THREAD_GETMEM (self, cleanup);
 
-  int cancelhandling = THREAD_GETMEM (self, cancelhandling);
-
   /* Disable asynchronous cancellation for now.  */
-  if (__glibc_unlikely (cancelhandling & CANCELTYPE_BITMASK))
-    while (1)
-      {
-	int curval = THREAD_ATOMIC_CMPXCHG_VAL (self, cancelhandling,
-						cancelhandling
-						& ~CANCELTYPE_BITMASK,
-						cancelhandling);
-	if (__glibc_likely (curval == cancelhandling))
-	  /* Successfully replaced the value.  */
-	  break;
-
-	/* Prepare for the next round.  */
-	cancelhandling = curval;
-      }
-
-  buffer->__canceltype = (cancelhandling & CANCELTYPE_BITMASK
-			  ? PTHREAD_CANCEL_ASYNCHRONOUS
-			  : PTHREAD_CANCEL_DEFERRED);
+  buffer->__canceltype = THREAD_GETMEM (self, canceltype);
+  THREAD_SETMEM (self, canceltype, PTHREAD_CANCEL_DEFERRED);
 
   THREAD_SETMEM (self, cleanup, buffer);
 }
@@ -60,26 +42,8 @@ __libc_cleanup_pop_restore (struct _pthread_cleanup_buffer *buffer)
 
   THREAD_SETMEM (self, cleanup, buffer->__prev);
 
-  int cancelhandling;
-  if (__builtin_expect (buffer->__canceltype != PTHREAD_CANCEL_DEFERRED, 0)
-      && ((cancelhandling = THREAD_GETMEM (self, cancelhandling))
-	  & CANCELTYPE_BITMASK) == 0)
-    {
-      while (1)
-	{
-	  int curval = THREAD_ATOMIC_CMPXCHG_VAL (self, cancelhandling,
-						  cancelhandling
-						  | CANCELTYPE_BITMASK,
-						  cancelhandling);
-	  if (__glibc_likely (curval == cancelhandling))
-	    /* Successfully replaced the value.  */
-	    break;
-
-	  /* Prepare for the next round.  */
-	  cancelhandling = curval;
-	}
-
+  THREAD_SETMEM (self, canceltype, buffer->__canceltype);
+  if (buffer->__canceltype == PTHREAD_CANCEL_ASYNCHRONOUS)
       __pthread_testcancel ();
-    }
 }
 libc_hidden_def (__libc_cleanup_pop_restore)
diff --git a/nptl/pthread_cancel.c b/nptl/pthread_cancel.c
index f4f0836..de4659a 100644
--- a/nptl/pthread_cancel.c
+++ b/nptl/pthread_cancel.c
@@ -53,7 +53,7 @@ sigcancel_handler (int sig, siginfo_t *si, void *ctx)
   /* Set the return value.  */
   THREAD_SETMEM (self, result, PTHREAD_CANCELED);
   /* Make sure asynchronous cancellation is still enabled.  */
-  if ((ch & CANCELTYPE_BITMASK) != 0)
+  if (self->canceltype == PTHREAD_CANCEL_ASYNCHRONOUS)
     __do_cancel ();
 }
 
@@ -104,8 +104,8 @@ __pthread_cancel (pthread_t th)
 #endif
 
       THREAD_SETMEM (pd, result, PTHREAD_CANCELED);
-      if ((oldch & CANCELSTATE_BITMASK) == 0
-	  && (oldch & CANCELTYPE_BITMASK) != 0)
+      if (pd->cancelstate == PTHREAD_CANCEL_ENABLE
+	  && pd->canceltype == PTHREAD_CANCEL_ASYNCHRONOUS)
 	__do_cancel ();
       return 0;
     }
diff --git a/nptl/pthread_setcanceltype.c b/nptl/pthread_setcanceltype.c
index ae5df1d..e7b24ae 100644
--- a/nptl/pthread_setcanceltype.c
+++ b/nptl/pthread_setcanceltype.c
@@ -29,43 +29,11 @@ __pthread_setcanceltype (int type, int *oldtype)
 
   volatile struct pthread *self = THREAD_SELF;
 
-  int oldval = THREAD_GETMEM (self, cancelhandling);
-  while (1)
-    {
-      int newval = (type == PTHREAD_CANCEL_ASYNCHRONOUS
-		    ? oldval | CANCELTYPE_BITMASK
-		    : oldval & ~CANCELTYPE_BITMASK);
-
-      /* Store the old value.  */
-      if (oldtype != NULL)
-	*oldtype = ((oldval & CANCELTYPE_BITMASK)
-		    ? PTHREAD_CANCEL_ASYNCHRONOUS : PTHREAD_CANCEL_DEFERRED);
-
-      /* Avoid doing unnecessary work.  The atomic operation can
-	 potentially be expensive if the memory has to be locked and
-	 remote cache lines have to be invalidated.  */
-      if (oldval == newval)
-	break;
-
-      /* Update the cancel handling word.  This has to be done
-	 atomically since other bits could be modified as well.  */
-      int curval = THREAD_ATOMIC_CMPXCHG_VAL (self, cancelhandling, newval,
-					      oldval);
-      if (__glibc_likely (curval == oldval))
-	{
-	  if (self->cancelstate == PTHREAD_CANCEL_ENABLE
-	      && CANCEL_CANCELED_AND_ASYNCHRONOUS (newval))
-	    {
-	      THREAD_SETMEM (self, result, PTHREAD_CANCELED);
-	      __do_cancel ();
-	    }
-
-	  break;
-	}
-
-      /* Prepare for the next round.  */
-      oldval = curval;
-    }
+  if (oldtype != NULL)
+    *oldtype = self->canceltype;
+  self->canceltype = type;
+  if (type == PTHREAD_CANCEL_ASYNCHRONOUS)
+    __pthread_testcancel ();
 
   return 0;
 }
diff --git a/sysdeps/nptl/dl-tls_init_tp.c b/sysdeps/nptl/dl-tls_init_tp.c
index 378b26a..b7b3bb1 100644
--- a/sysdeps/nptl/dl-tls_init_tp.c
+++ b/sysdeps/nptl/dl-tls_init_tp.c
@@ -96,4 +96,5 @@ __tls_init_tp (void)
   THREAD_SETMEM (pd, stackblock_size, (size_t) __libc_stack_end);
 
   THREAD_SETMEM (pd, cancelstate, PTHREAD_CANCEL_ENABLE);
+  THREAD_SETMEM (pd, canceltype, PTHREAD_CANCEL_DEFERRED);
 }