[PATCH bpf-next v3 1/3] bpf: Add bpf_tail_call_cnt to task_struct

[Leon Hwang <hffilwlqm@gmail.com>]

In order to get rid of propagating tail call counter by rax and stack,
it's to store tail call counter at task_struct.

Then, at the prologue of bpf prog, it has to initialise the tail call
counter at task_struct. And when tail call happens, it has to compare
and increment the tail call counter at task_struct.

Signed-off-by: Leon Hwang <hffilwlqm@gmail.com>
---
 include/linux/sched.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 3c2abbc587b49..d0696fcabf14f 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1501,6 +1501,8 @@ struct task_struct {
 	struct bpf_local_storage __rcu	*bpf_storage;
 	/* Used for BPF run context */
 	struct bpf_run_ctx		*bpf_ctx;
+	/* Used for BPF run time */
+	u32				bpf_tail_call_cnt;
 #endif
 
 #ifdef CONFIG_GCC_PLUGIN_STACKLEAK
-- 
2.44.0