[glibc/azanella/posix_spawn-clone3] Linux: optimize clone3 internal usage

[glibc/azanella/posix_spawn-clone3] Linux: optimize clone3 internal usage

[Adhemerval Zanella]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=c644b43efe494c57a58aa532d4686375d5e6ecbf

commit c644b43efe494c57a58aa532d4686375d5e6ecbf
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date:   Wed Sep 28 10:24:06 2022 -0300

    Linux: optimize clone3 internal usage
    
    Now that clone3 is used on more architectures, add an optimization
    to avoid calling when glibc detects that it is no supported by the
    kernel.  It also adds __ASSUME_CLONE3, which allows skip this
    optimization and issue clone3 syscall directly.
    
    It does not handle the the small window between 5.3 and 5.5 for
    posix_spawn (CLONE_CLEAR_SIGHAND was added in 5.5).
    
    Checked on x86_64-linux-gnu.

Diff:
---
 include/clone_internal.h                  |  5 +++++
 sysdeps/unix/sysv/linux/clone-internal.c  | 24 +++++++++++++++++++++++-
 sysdeps/unix/sysv/linux/kernel-features.h |  9 +++++++++
 3 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/include/clone_internal.h b/include/clone_internal.h
index 81292b3eb1..5f936dd8dc 100644
--- a/include/clone_internal.h
+++ b/include/clone_internal.h
@@ -26,6 +26,11 @@ extern int __clone3 (struct clone_args *__cl_args, size_t __size,
    fall back to clone or clone2.  */
 extern int __clone_internal (struct clone_args *__cl_args,
 			     int (*__func) (void *__arg), void *__arg);
+/* clone3 wrapper with a sticky check to avoid re-issue the syscall if
+   it fails with ENOSYS.  */
+extern int __clone3_internal (struct clone_args *cl_args,
+			      int (*func) (void *args), void *arg)
+     attribute_hidden;
 /* The fallback code which calls clone/clone2 based on clone3 arguments.  */
 extern int __clone_internal_fallback (struct clone_args *__cl_args,
 				      int (*__func) (void *__arg),
diff --git a/sysdeps/unix/sysv/linux/clone-internal.c b/sysdeps/unix/sysv/linux/clone-internal.c
index 7bc991e033..39d76733db 100644
--- a/sysdeps/unix/sysv/linux/clone-internal.c
+++ b/sysdeps/unix/sysv/linux/clone-internal.c
@@ -76,6 +76,28 @@ __clone_internal_fallback (struct clone_args *cl_args,
   return ret;
 }
 
+int
+__clone3_internal (struct clone_args *cl_args, int (*func) (void *args),
+		   void *arg)
+{
+#ifdef HAVE_CLONE3_WRAPPER
+# if __ASSUME_CLONE3
+  return __clone3 (cl_args, sizeof (*cl_args), func, arg);
+# else
+  static int clone3_supported = 1;
+  if (atomic_load_relaxed (&clone3_supported) == 1)
+    {
+      int ret = __clone3 (cl_args, sizeof (*cl_args), func, arg);
+      if (ret != -1 || errno != ENOSYS)
+	return ret;
+
+      atomic_store_relaxed (&clone3_supported, 0);
+    }
+# endif
+#endif
+  __set_errno (ENOSYS);
+  return -1;
+}
 
 int
 __clone_internal (struct clone_args *cl_args,
@@ -83,7 +105,7 @@ __clone_internal (struct clone_args *cl_args,
 {
 #ifdef HAVE_CLONE3_WRAPPER
   int saved_errno = errno;
-  int ret = __clone3 (cl_args, sizeof (*cl_args), func, arg);
+  int ret = __clone3_internal (cl_args, func, arg);
   if (ret != -1 || errno != ENOSYS)
     return ret;
 
diff --git a/sysdeps/unix/sysv/linux/kernel-features.h b/sysdeps/unix/sysv/linux/kernel-features.h
index 74adc3956b..4ecd08a98f 100644
--- a/sysdeps/unix/sysv/linux/kernel-features.h
+++ b/sysdeps/unix/sysv/linux/kernel-features.h
@@ -236,4 +236,13 @@
 # define __ASSUME_FUTEX_LOCK_PI2 0
 #endif
 
+/* The clone3 system call was introduced across on most architectures in
+   Linux 5.3.  Not all ports implements it, so it should be used along
+   HAVE_CLONE3_WRAPPER define.  */
+#if __LINUX_KERNEL_VERSION >= 0x050300
+# define __ASSUME_CLONE3 1
+#else
+# define __ASSUME_CLONE3 0
+#endif
+
 #endif /* kernel-features.h */