From: Andrea Righi <arighi@nvidia.com> mainline inclusion from mainline-v6.14-rc3 commit 1626e5ef0b00386a4fd083fa7c46c8edbd75f9b4 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/IDC9YK Reference: https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commi... -------------------------------- While performing the rq locking dance in dispatch_to_local_dsq(), we may trigger the following lock imbalance condition, in particular when multiple tasks are rapidly changing CPU affinity (i.e., running a `stress-ng --race-sched 0`): [ 13.413579] ===================================== [ 13.413660] WARNING: bad unlock balance detected! [ 13.413729] 6.13.0-virtme #15 Not tainted [ 13.413792] ------------------------------------- [ 13.413859] kworker/1:1/80 is trying to release lock (&rq->__lock) at: [ 13.413954] [<ffffffff873c6c48>] dispatch_to_local_dsq+0x108/0x1a0 [ 13.414111] but there are no more locks to release! [ 13.414176] [ 13.414176] other info that might help us debug this: [ 13.414258] 1 lock held by kworker/1:1/80: [ 13.414318] #0: ffff8b66feb41698 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x20/0x90 [ 13.414612] [ 13.414612] stack backtrace: [ 13.415255] CPU: 1 UID: 0 PID: 80 Comm: kworker/1:1 Not tainted 6.13.0-virtme #15 [ 13.415505] Workqueue: 0x0 (events) [ 13.415567] Sched_ext: dsp_local_on (enabled+all), task: runnable_at=-2ms [ 13.415570] Call Trace: [ 13.415700] <TASK> [ 13.415744] dump_stack_lvl+0x78/0xe0 [ 13.415806] ? dispatch_to_local_dsq+0x108/0x1a0 [ 13.415884] print_unlock_imbalance_bug+0x11b/0x130 [ 13.415965] ? dispatch_to_local_dsq+0x108/0x1a0 [ 13.416226] lock_release+0x231/0x2c0 [ 13.416326] _raw_spin_unlock+0x1b/0x40 [ 13.416422] dispatch_to_local_dsq+0x108/0x1a0 [ 13.416554] flush_dispatch_buf+0x199/0x1d0 [ 13.416652] balance_one+0x194/0x370 [ 13.416751] balance_scx+0x61/0x1e0 [ 13.416848] prev_balance+0x43/0xb0 [ 13.416947] __pick_next_task+0x6b/0x1b0 [ 13.417052] __schedule+0x20d/0x1740 This happens because dispatch_to_local_dsq() is racing with dispatch_dequeue() and, when the latter wins, we incorrectly assume that the task has been moved to dst_rq. Fix by properly tracking the currently locked rq. Fixes: 4d3ca89bdd31 ("sched_ext: Refactor consume_remote_task()") Signed-off-by: Andrea Righi <arighi@nvidia.com> Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Zicheng Qu <quzicheng@huawei.com> --- kernel/sched/ext.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index b98de1532d6c..53cd45cf4fcc 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -2584,6 +2584,9 @@ static void dispatch_to_local_dsq(struct rq *rq, struct scx_dispatch_q *dst_dsq, { struct rq *src_rq = task_rq(p); struct rq *dst_rq = container_of(dst_dsq, struct rq, scx.local_dsq); +#ifdef CONFIG_SMP + struct rq *locked_rq = rq; +#endif /* * We're synchronized against dequeue through DISPATCHING. As @p can't @@ -2620,8 +2623,9 @@ static void dispatch_to_local_dsq(struct rq *rq, struct scx_dispatch_q *dst_dsq, atomic_long_set_release(&p->scx.ops_state, SCX_OPSS_NONE); /* switch to @src_rq lock */ - if (rq != src_rq) { - raw_spin_rq_unlock(rq); + if (locked_rq != src_rq) { + raw_spin_rq_unlock(locked_rq); + locked_rq = src_rq; raw_spin_rq_lock(src_rq); } @@ -2639,6 +2643,8 @@ static void dispatch_to_local_dsq(struct rq *rq, struct scx_dispatch_q *dst_dsq, } else { move_remote_task_to_local_dsq(p, enq_flags, src_rq, dst_rq); + /* task has been moved to dst_rq, which is now locked */ + locked_rq = dst_rq; } /* if the destination CPU is idle, wake it up */ @@ -2647,8 +2653,8 @@ static void dispatch_to_local_dsq(struct rq *rq, struct scx_dispatch_q *dst_dsq, } /* switch back to @rq lock */ - if (rq != dst_rq) { - raw_spin_rq_unlock(dst_rq); + if (locked_rq != rq) { + raw_spin_rq_unlock(locked_rq); raw_spin_rq_lock(rq); } #else /* CONFIG_SMP */ -- 2.34.1