Commit 851a723e45 ("sched: Always clear user_cpus_ptr in
do_set_cpus_allowed()") added a kfree() call to free any user
provided affinity mask, if present. It was changed later to use
kfree_rcu() in commit 9a5418bc48 ("sched/core: Use kfree_rcu()
in do_set_cpus_allowed()") to avoid a circular locking dependency
problem.
It turns out that even kfree_rcu() isn't safe for avoiding
circular locking problem. As reported by kernel test robot,
the following circular locking dependency now exists:
&rdp->nocb_lock --> rcu_node_0 --> &rq->__lock
Solve this by breaking the rcu_node_0 --> &rq->__lock chain by moving
the resched_cpu() out from under rcu_node lock.
[peterz: heavily borrowed from Waiman's Changelog]
[paulmck: applied Z qiang feedback]
Fixes: 851a723e45 ("sched: Always clear user_cpus_ptr in do_set_cpus_allowed()")
Reported-by: kernel test robot <oliver.sang@intel.com>
Acked-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/oe-lkp/202310302207.a25f1a30-oliver.sang@intel.com
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
85d68222dd