btf: Add a new kfunc flag which allows to mark a function to be sleepable

This allows to declare a kfunc as sleepable and prevents its use in
a non sleepable program.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Co-developed-by: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Hao Luo <haoluo@google.com>
Link: https://lore.kernel.org/r/20220805214821.1058337-2-haoluo@google.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/linux/btf.h

@@ -49,6 +49,7 @@
  * for this case.
  */
 #define KF_TRUSTED_ARGS (1 << 4) /* kfunc only takes trusted pointer arguments */
+#define KF_SLEEPABLE   (1 << 5) /* kfunc may sleep */
 
 struct btf;
 struct btf_member;