Commit 1d10bf55 authored May 25, 2021 by Paul E. McKenney

rcu-tasks: Don't delete holdouts within trc_inspect_reader()



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@windriver.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

parent 05bc276c

kernel/rcu/tasks.h

+2 −3

Original line number	Diff line number	Diff line
		@@ -953,10 +953,9 @@ 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!!!