The following commit has been merged into the sched/core branch of tip: Commit-ID: ded467dc83ac7173f1532bb0faa25022ff8769e5 Gitweb: https://git.kernel.org/tip/ded467dc83ac7173f1532bb0faa25022ff8769e5 Author: Peter Zijlstra <[email protected]> AuthorDate: Thu, 01 Oct 2020 16:13:01 +02:00 Committer: Peter Zijlstra <[email protected]> CommitterDate: Tue, 10 Nov 2020 18:39:01 +01:00
sched, lockdep: Annotate ->pi_lock recursion There's a valid ->pi_lock recursion issue where the actual PI code tries to wake up the stop task. Make lockdep aware so it doesn't complain about this. Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Reviewed-by: Valentin Schneider <[email protected]> Reviewed-by: Daniel Bristot de Oliveira <[email protected]> Link: https://lkml.kernel.org/r/[email protected] --- kernel/sched/core.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 6ea593c..9ce2fc7 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2658,6 +2658,7 @@ int select_task_rq(struct task_struct *p, int cpu, int sd_flags, int wake_flags) void sched_set_stop_task(int cpu, struct task_struct *stop) { + static struct lock_class_key stop_pi_lock; struct sched_param param = { .sched_priority = MAX_RT_PRIO - 1 }; struct task_struct *old_stop = cpu_rq(cpu)->stop; @@ -2673,6 +2674,20 @@ void sched_set_stop_task(int cpu, struct task_struct *stop) sched_setscheduler_nocheck(stop, SCHED_FIFO, ¶m); stop->sched_class = &stop_sched_class; + + /* + * The PI code calls rt_mutex_setprio() with ->pi_lock held to + * adjust the effective priority of a task. As a result, + * rt_mutex_setprio() can trigger (RT) balancing operations, + * which can then trigger wakeups of the stop thread to push + * around the current task. + * + * The stop task itself will never be part of the PI-chain, it + * never blocks, therefore that ->pi_lock recursion is safe. + * Tell lockdep about this by placing the stop->pi_lock in its + * own class. + */ + lockdep_set_class(&stop->pi_lock, &stop_pi_lock); } cpu_rq(cpu)->stop = stop;
