On Thu, Feb 22, 2024 at 12:41:55PM -0800, Paul E. McKenney wrote: > On Thu, Feb 22, 2024 at 05:21:03PM +0100, Frederic Weisbecker wrote: > > Le Fri, Feb 16, 2024 at 05:27:38PM -0800, Boqun Feng a écrit : > > > From: "Paul E. McKenney" <paulmck@xxxxxxxxxx> > > > > > > Holding a mutex across synchronize_rcu_tasks() and acquiring > > > that same mutex in code called from do_exit() after its call to > > > exit_tasks_rcu_start() but before its call to exit_tasks_rcu_stop() > > > results in deadlock. This is by design, because tasks that are far > > > enough into do_exit() are no longer present on the tasks list, making > > > it a bit difficult for RCU Tasks to find them, let alone wait on them > > > to do a voluntary context switch. However, such deadlocks are becoming > > > more frequent. In addition, lockdep currently does not detect such > > > deadlocks and they can be difficult to reproduce. > > > > > > In addition, if a task voluntarily context switches during that time > > > (for example, if it blocks acquiring a mutex), then this task is in an > > > RCU Tasks quiescent state. And with some adjustments, RCU Tasks could > > > just as well take advantage of that fact. > > > > > > This commit therefore initializes the data structures that will be needed > > > to rely on these quiescent states and to eliminate these deadlocks. > > > > > > Link: https://lore.kernel.org/all/20240118021842.290665-1-chenzhongjin@xxxxxxxxxx/ > > > > > > Reported-by: Chen Zhongjin <chenzhongjin@xxxxxxxxxx> > > > Reported-by: Yang Jihong <yangjihong1@xxxxxxxxxx> > > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > > > Tested-by: Yang Jihong <yangjihong1@xxxxxxxxxx> > > > Tested-by: Chen Zhongjin <chenzhongjin@xxxxxxxxxx> > > > Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx> Looks good, thanks! Reviewed-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
