rcu: Synchronize ->qsmaskinitnext in rcu_boost_kthread_setaffinity()

Once either rcutree_online_cpu() or rcutree_dead_cpu() is invoked
concurrently, the following rcu_boost_kthread_setaffinity() race can
occur:

        CPU 1                               CPU2
mask = rcu_rnp_online_cpus(rnp);
...

                                   mask = rcu_rnp_online_cpus(rnp);
                                   ...
                                   set_cpus_allowed_ptr(t, cm);

set_cpus_allowed_ptr(t, cm);

This results in CPU2's update being overwritten by that of CPU1, and
thus the possibility of ->boost_kthread_task continuing to run on a
to-be-offlined CPU.

This commit therefore eliminates this race by relying on the pre-existing
acquisition of ->boost_kthread_mutex to serialize the full process of
changing the affinity of ->boost_kthread_task.

Signed-off-by: Pingfan Liu <[email protected]>
Cc: David Woodhouse <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Neeraj Upadhyay <[email protected]>
Cc: Josh Triplett <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Lai Jiangshan <[email protected]>
Cc: Joel Fernandes <[email protected]>
Cc: "Jason A. Donenfeld" <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>

0 files changed, 0 insertions, 0 deletions