[PATCH] sched: set TIF_NEED_RESCHED before calling __trace_set_need_resched()

[Sechang Lim]

set_tsk_need_resched() tests TIF_NEED_RESCHED, calls
__trace_set_need_resched() if the flag is clear, then sets it via
set_tsk_thread_flag().  A BPF raw_tp program attached to
sched_set_need_resched executes synchronously inside __bpf_trace_run().
On return, __bpf_trace_run() drops the RCU lock with
rcu_read_unlock_migrate(), which on the preempt-or-BH-disabled path
calls set_need_resched_current() -> set_tsk_need_resched() again.

set_tsk_thread_flag() follows the tracepoint call, so every re-entrant
frame sees TIF_NEED_RESCHED clear and calls __trace_set_need_resched()
again:

  BUG: TASK stack guard page was hit at ffffc9001224ff98
  Oops: stack guard page: 0000 [#1] SMP KASAN PTI
  RIP: 0010:__bpf_trace_sched_set_need_resched_tp+0x1c/0x190
  Call Trace:
   trace_sched_set_need_resched_tp+0x110/0x130
   set_tsk_need_resched include/linux/sched.h:2076
   set_need_resched_current include/linux/sched.h:2094
   rcu_read_unlock_special+0x43a/0x440
   __rcu_read_unlock+0x9e/0x120
   rcu_read_unlock_migrate+0xa9/0x240
   __bpf_trace_run+0x131/0x180
   bpf_trace_run3+0x333/0x430
   __bpf_trace_sched_set_need_resched_tp+0x13a/0x190
   trace_sched_set_need_resched_tp+0x110/0x130
   set_tsk_need_resched include/linux/sched.h:2076
   ...

Replace the separate test_tsk_thread_flag() + set_tsk_thread_flag() pair
with test_and_set_tsk_thread_flag().

Fixes: adcc3bfa8806 ("sched: Adapt sched tracepoints for RV task model")
Signed-off-by: Sechang Lim <rhkrqnwk98@xxxxxxxxx>
---
 include/linux/sched.h | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index ee06cba5c6f5..c9efd08dae92 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2071,10 +2071,9 @@ static inline int test_tsk_thread_flag(struct task_struct *tsk, int flag)
 
 static inline void set_tsk_need_resched(struct task_struct *tsk)
 {
-	if (tracepoint_enabled(sched_set_need_resched_tp) &&
-	    !test_tsk_thread_flag(tsk, TIF_NEED_RESCHED))
+	if (!test_and_set_tsk_thread_flag(tsk, TIF_NEED_RESCHED) &&
+	    tracepoint_enabled(sched_set_need_resched_tp))
 		__trace_set_need_resched(tsk, TIF_NEED_RESCHED);
-	set_tsk_thread_flag(tsk,TIF_NEED_RESCHED);
 }
 
 static inline void clear_tsk_need_resched(struct task_struct *tsk)
-- 
2.43.0