[glibc] Linux: optimize clone3 internal usage

[glibc] Linux: optimize clone3 internal usage

[Adhemerval Zanella]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=98f9435f336cbee5d57a1a16373331ca1bc648db

commit 98f9435f336cbee5d57a1a16373331ca1bc648db
Author: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
Date:   Thu Jan 12 10:58:53 2023 -0300

    Linux: optimize clone3 internal usage
    
    Add an optimization to avoid calling clone3 when glibc detects that
    there is no kernel support.  It also adds __ASSUME_CLONE3, which allows
    skipping this optimization and issuing the 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.
    Reviewed-by: Carlos O'Donell <carlos@redhat.com>

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 3b6cd85f02..dd380f119e 100644
--- a/include/clone_internal.h
+++ b/include/clone_internal.h
@@ -24,6 +24,11 @@ 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-issuing 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 e125c9125e..790739cfce 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 a23d0079a1..4b5c4afbc1 100644
--- a/sysdeps/unix/sysv/linux/kernel-features.h
+++ b/sysdeps/unix/sysv/linux/kernel-features.h
@@ -241,4 +241,13 @@
 # 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 */