trc_del_holdout() invokes put_task_struct() may cause the task_struct
is freed once the task is exiting. If happened, then we shouldn't touch
the task_strcut, or it will triger an use-after-free. Here we only mark
it as checked, and grace-period kthread will romove it from holdout
list.
CPU0 CPU1
trc_add_holdout(t, bhp)
//t->usage==2
......
......
release_task
->put_task_struct_rcu_user
->delayed_put_task_struct
......
->put_task_struct(t)
//t->usage==1
check_all_holdout_tasks_trace
->trc_wait_for_one_reader
->get_task_struct
->try_invoke_on_locked_down_task(trc_inspect_reader)
->trc_del_holdout
->put_task_struct(t)
//t->usage==0 and task_struct freed
->READ_ONCE(t->trc_reader_checked)
//ops, t had been freed.
BTW, do the same thing in trc_wait_for_one_reader() when the task is a
current running task even if it is safe.
Reported-by: [email protected]
Signed-off-by: Yanfei Xu <[email protected]>
---
v1->v2:
1. improve the commit messages.
2. change the comments in codes.
kernel/rcu/tasks.h | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 36607551f966..2303cb131367 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -872,10 +872,9 @@ static bool trc_inspect_reader(struct task_struct *t, void *arg)
in_qs = likely(!t->trc_reader_nesting);
}
- // Mark as checked. Because this is called from the grace-period
- // kthread, also remove the task from the holdout list.
+ // Mark as checked so that the grace-period kthread will
+ // remove it from the holdout list.
t->trc_reader_checked = true;
- trc_del_holdout(t);
if (in_qs)
return true; // Already in quiescent state, done!!!
@@ -899,10 +898,11 @@ static void trc_wait_for_one_reader(struct task_struct *t,
if (smp_load_acquire(&t->trc_ipi_to_cpu) != -1) // Order IPI
return;
- // The current task had better be in a quiescent state.
+ // The current task had better be in a quiescent state, and
+ // mark as checked so that the grace-period kthread will
+ // remove it from the holdout list.
if (t == current) {
t->trc_reader_checked = true;
- trc_del_holdout(t);
WARN_ON_ONCE(t->trc_reader_nesting);
return;
}
--
2.27.0