This is a note to let you know that I've just added the patch titled rcu-tasks: Don't delete holdouts within trc_inspect_reader() to the 5.10-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: rcu-tasks-don-t-delete-holdouts-within-trc_inspect_r.patch and it can be found in the queue-5.10 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit d87510da0f7d9b8ad77b329a3f2f5932952fa898 Author: Paul E. McKenney <paulmck@xxxxxxxxxx> Date: Tue May 25 10:12:45 2021 -0700 rcu-tasks: Don't delete holdouts within trc_inspect_reader() [ Upstream commit 1d10bf55d85d34eb73dd8263635f43fd72135d2d ] As Yanfei pointed out, although invoking trc_del_holdout() is safe from the viewpoint of the integrity of the holdout list itself, the put_task_struct() invoked by trc_del_holdout() can result in use-after-free errors due to later accesses to this task_struct structure by the RCU Tasks Trace grace-period kthread. This commit therefore removes this call to trc_del_holdout() from trc_inspect_reader() in favor of the grace-period thread's existing call to trc_del_holdout(), thus eliminating that particular class of use-after-free errors. Reported-by: "Xu, Yanfei" <yanfei.xu@xxxxxxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index 73bbe792fe1e..208acb286ec2 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -879,10 +879,9 @@ 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!!!