On Fri, Sep 08, 2023 at 10:36:03PM +0200, Frederic Weisbecker wrote: > The callbacks migration is performed through an explicit call from > the hotplug control CPU right after the death of the target CPU and > before proceeding with the CPUHP_ teardown functions. > > This is unusual but necessary and yet uncommented. Summarize the reason > as explained in the changelog of: > > a58163d8ca2c (rcu: Migrate callbacks earlier in the CPU-offline timeline) > > Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx> Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > --- > kernel/cpu.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/kernel/cpu.c b/kernel/cpu.c > index a41a6fff3c91..b135bb481be1 100644 > --- a/kernel/cpu.c > +++ b/kernel/cpu.c > @@ -1352,7 +1352,14 @@ static int takedown_cpu(unsigned int cpu) > cpuhp_bp_sync_dead(cpu); > > tick_cleanup_dead_cpu(cpu); > + > + /* > + * Callbacks must be re-integrated right away to the RCU state machine. > + * Otherwise an RCU callback could block a further teardown function > + * waiting for its completion. > + */ > rcutree_migrate_callbacks(cpu); > + > return 0; > } > > -- > 2.41.0 >
