Refactor PI mutexes internal definitions

This patch adds the generic futex_lock_pi and futex_unlock_pi to wrap
around the syscall machinery required to issue the syscall calls. It
simplifies a bit the futex code required to implement PI mutexes.

No function changes, checked on x86_64-linux-gnu.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

sysdeps/nptl/futex-internal.h

@@ -381,4 +381,90 @@ futex_wake (unsigned int* futex_word, int processes_to_wake, int private)
     }
 }
 
+/* The operation checks the value of the futex, if the value is 0, then
+   it is atomically set to the caller's thread ID.  If the futex value is
+   nonzero, it is atomically sets the FUTEX_WAITERS bit, which signals wrt
+   other futex owner that it cannot unlock the futex in user space by
+   atomically by setting its value to 0.
+
+   If more than one wait operations is issued, the enqueueing of the waiters
+   are done in descending priority order.
+
+   The ABSTIME arguments provides an absolute timeout (measured against the
+   CLOCK_REALTIME clock).  If TIMEOUT is NULL, the operation will block
+   indefinitely.
+
+   Returns:
+
+     - 0 if woken by a PI unlock operation or spuriously.
+     - EAGAIN if the futex owner thread ID is about to exit, but has not yet
+       handled the state cleanup.
+     - EDEADLK if the futex is already locked by the caller.
+     - ESRCH if the thread ID int he futex does not exist.
+     - EINVAL is the state is corrupted or if there is a waiter on the
+       futex.
+     - ETIMEDOUT if the ABSTIME expires.
+*/
+static __always_inline int
+futex_lock_pi (unsigned int *futex_word, const struct timespec *abstime,
+	       int private)
+{
+  int err = lll_futex_timed_lock_pi (futex_word, abstime, private);
+  switch (err)
+    {
+    case 0:
+    case -EAGAIN:
+    case -EINTR:
+    case -ETIMEDOUT:
+    case -ESRCH:
+    case -EDEADLK:
+    case -EINVAL: /* This indicates either state corruption or that the kernel
+		     found a waiter on futex address which is waiting via
+		     FUTEX_WAIT or FUTEX_WAIT_BITSET.  This is reported on
+		     some futex_lock_pi usage (pthread_mutex_timedlock for
+		     instance).  */
+      return -err;
+
+    case -EFAULT: /* Must have been caused by a glibc or application bug.  */
+    case -ENOSYS: /* Must have been caused by a glibc bug.  */
+    /* No other errors are documented at this time.  */
+    default:
+      futex_fatal_error ();
+    }
+}
+
+/* Wakes the top priority waiter that called a futex_lock_pi operation on
+   the futex.
+
+   Returns the same values as futex_lock_pi under those same conditions;
+   additionally, returns EPERM when the caller is not allowed to attach
+   itself to the futex.  */
+static __always_inline int
+futex_unlock_pi (unsigned int *futex_word, int private)
+{
+  int err = lll_futex_timed_unlock_pi (futex_word, private);
+  switch (err)
+    {
+    case 0:
+    case -EAGAIN:
+    case -EINTR:
+    case -ETIMEDOUT:
+    case -ESRCH:
+    case -EDEADLK:
+    case -ENOSYS:
+    case -EPERM:  /*  The caller is not allowed to attach itself to the futex.
+		      Used to check if PI futexes are supported by the
+		      kernel.  */
+      return -err;
+
+    case -EINVAL: /* Either due to wrong alignment or due to the timeout not
+		     being normalized.  Must have been caused by a glibc or
+		     application bug.  */
+    case -EFAULT: /* Must have been caused by a glibc or application bug.  */
+    /* No other errors are documented at this time.  */
+    default:
+      futex_fatal_error ();
+    }
+}
+
 #endif  /* futex-internal.h */