[PATCH v3 1/6] exit: perform add_device_randomness() without tasklist_lock

Mateusz Guzik
2025-02-01T16:31:24Z

Parallel calls to add_device_randomness() contend on their own.

The clone side aleady runs outside of tasklist_lock, which in turn means
any caller on the exit side extends the tasklist_lock hold time while
contending on the random-private lock.

Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
---
kernel/exit.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 3485e5fc499e..1eb2e7d36ce4 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -174,9 +174,6 @@ static void __exit_signal(struct task_struct *tsk)
sig->curr_target = next_thread(tsk);
}

- add_device_randomness((const void*) &tsk->se.sum_exec_runtime,
- sizeof(unsigned long long));
-
/*
* Accumulate here the counters for all threads as they die. We could
* skip the group leader because it is the last user of signal_struct,
@@ -278,6 +275,8 @@ void release_task(struct task_struct *p)
write_unlock_irq(&tasklist_lock);
proc_flush_pid(thread_pid);
put_pid(thread_pid);
+ add_device_randomness((const void*) &p->se.sum_exec_runtime,
+ sizeof(unsigned long long));
release_thread(p);
put_task_struct_rcu_user(p);

--
2.43.0