futex: Update comments and docs about return values of arch futex code

The architecture implementations of 'arch_futex_atomic_op_inuser()' and 'futex_atomic_cmpxchg_inatomic()' are permitted to return only -EFAULT, -EAGAIN or -ENOSYS in the case of failure. Update the comments in the asm-generic/ implementation and also a stray reference in the robust futex documentation. Signed-off-by: Will Deacon <[email protected]>
berg · Apr 26, 2019 · 4275035 · 4275035
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diff --git a/Documentation/robust-futexes.txt b/Documentation/robust-futexes.txt
@@ -218,5 +218,4 @@ All other architectures should build just fine too - but they won't have
 the new syscalls yet.
 
 Architectures need to implement the new futex_atomic_cmpxchg_inatomic()
-inline function before writing up the syscalls (that function returns
--ENOSYS right now).
+inline function before writing up the syscalls.
diff --git a/include/asm-generic/futex.h b/include/asm-generic/futex.h
@@ -23,7 +23,9 @@
  *
  * Return:
  * 0 - On success
- * <0 - On error
+ * -EFAULT - User access resulted in a page fault
+ * -EAGAIN - Atomic operation was unable to complete due to contention
+ * -ENOSYS - Operation not supported
  */
 static inline int
 arch_futex_atomic_op_inuser(int op, u32 oparg, int *oval, u32 __user *uaddr)
@@ -85,7 +87,9 @@ arch_futex_atomic_op_inuser(int op, u32 oparg, int *oval, u32 __user *uaddr)
  *
  * Return:
  * 0 - On success
- * <0 - On error
+ * -EFAULT - User access resulted in a page fault
+ * -EAGAIN - Atomic operation was unable to complete due to contention
+ * -ENOSYS - Function not implemented (only if !HAVE_FUTEX_CMPXCHG)
  */
 static inline int
 futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,