mainline inclusion from mainline-v7.0-rc1 commit 94894c9c477e53bcea052e075c53f89df3d2a33e category: bugfix bugzilla: https://atomgit.com/openeuler/kernel/issues/8689 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- [ Upstream commit 94894c9c477e53bcea052e075c53f89df3d2a33e ] CPU0 becomes overloaded when hosting a CPU-bound RT task, a non-CPU-bound RT task, and a CFS task stuck in kernel space. When other CPUs switch from RT to non-RT tasks, RT load balancing (LB) is triggered; with HAVE_RT_PUSH_IPI enabled, they send IPIs to CPU0 to drive the execution of rto_push_irq_work_func. During push_rt_task on CPU0, if next_task->prio < rq->donor->prio, resched_curr() sets NEED_RESCHED and after the push operation completes, CPU0 calls rto_next_cpu(). Since only CPU0 is overloaded in this scenario, rto_next_cpu() should ideally return -1 (no further IPI needed). However, multiple CPUs invoking tell_cpu_to_push() during LB increments rd->rto_loop_next. Even when rd->rto_cpu is set to -1, the mismatch between rd->rto_loop and rd->rto_loop_next forces rto_next_cpu() to restart its search from -1. With CPU0 remaining overloaded (satisfying rt_nr_migratory && rt_nr_total > 1), it gets reselected, causing CPU0 to queue irq_work to itself and send self-IPIs repeatedly. As long as CPU0 stays overloaded and other CPUs run pull_rt_tasks(), it falls into an infinite self-IPI loop, which triggers a CPU hardlockup due to continuous self-interrupts. The trigging scenario is as follows: cpu0 cpu1 cpu2 pull_rt_task tell_cpu_to_push <------------irq_work_queue_on rto_push_irq_work_func push_rt_task resched_curr(rq) pull_rt_task rto_next_cpu tell_cpu_to_push <-------------------------- atomic_inc(rto_loop_next) rd->rto_loop != next rto_next_cpu irq_work_queue_on rto_push_irq_work_func Fix redundant self-IPI by filtering the initiating CPU in rto_next_cpu(). This solution has been verified to effectively eliminate spurious self-IPIs and prevent CPU hardlockup scenarios. Fixes: 4bdced5c9a29 ("sched/rt: Simplify the IPI based RT balancing logic") Suggested-by: Steven Rostedt (Google) <rostedt@goodmis.org> Suggested-by: K Prateek Nayak <kprateek.nayak@amd.com> Signed-off-by: Chen Jinghuang <chenjinghuang2@huawei.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org> Reviewed-by: Valentin Schneider <vschneid@redhat.com> Link: https://patch.msgid.link/20260122012533.673768-1-chenjinghuang2@huawei.com Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Chen Jinghuang <chenjinghuang2@huawei.com> --- kernel/sched/rt.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 549b9ecfda7d..48d53bf0161b 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -2231,6 +2231,7 @@ static void push_rt_tasks(struct rq *rq) */ static int rto_next_cpu(struct root_domain *rd) { + int this_cpu = smp_processor_id(); int next; int cpu; @@ -2254,6 +2255,10 @@ static int rto_next_cpu(struct root_domain *rd) rd->rto_cpu = cpu; + /* Do not send IPI to self */ + if (cpu == this_cpu) + continue; + if (cpu < nr_cpu_ids) return cpu; -- 2.34.1