6.18-stable review patch. If anyone has any objections, please let me know.
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From: Zqiang qiang.zhang@linux.dev
[ Upstream commit 1dd6c84f1c544e552848a8968599220bd464e338 ]
When loading the ebpf scheduler, the tasks in the scx_tasks list will be traversed and invoke __setscheduler_class() to get new sched_class. however, this would also incorrectly set the per-cpu migration task's->sched_class to rt_sched_class, even after unload, the per-cpu migration task's->sched_class remains sched_rt_class.
The log for this issue is as follows:
./scx_rustland --stats 1 [ 199.245639][ T630] sched_ext: "rustland" does not implement cgroup cpu.weight [ 199.269213][ T630] sched_ext: BPF scheduler "rustland" enabled 04:25:09 [INFO] RustLand scheduler attached
bpftrace -e 'iter:task /strcontains(ctx->task->comm, "migration")/ { printf("%s:%d->%pS\n", ctx->task->comm, ctx->task->pid, ctx->task->sched_class); }' Attaching 1 probe... migration/0:24->rt_sched_class+0x0/0xe0 migration/1:27->rt_sched_class+0x0/0xe0 migration/2:33->rt_sched_class+0x0/0xe0 migration/3:39->rt_sched_class+0x0/0xe0 migration/4:45->rt_sched_class+0x0/0xe0 migration/5:52->rt_sched_class+0x0/0xe0 migration/6:58->rt_sched_class+0x0/0xe0 migration/7:64->rt_sched_class+0x0/0xe0
sched_ext: BPF scheduler "rustland" disabled (unregistered from user space) EXIT: unregistered from user space 04:25:21 [INFO] Unregister RustLand scheduler
bpftrace -e 'iter:task /strcontains(ctx->task->comm, "migration")/ { printf("%s:%d->%pS\n", ctx->task->comm, ctx->task->pid, ctx->task->sched_class); }' Attaching 1 probe... migration/0:24->rt_sched_class+0x0/0xe0 migration/1:27->rt_sched_class+0x0/0xe0 migration/2:33->rt_sched_class+0x0/0xe0 migration/3:39->rt_sched_class+0x0/0xe0 migration/4:45->rt_sched_class+0x0/0xe0 migration/5:52->rt_sched_class+0x0/0xe0 migration/6:58->rt_sched_class+0x0/0xe0 migration/7:64->rt_sched_class+0x0/0xe0
This commit therefore generate a new scx_setscheduler_class() and add check for stop_sched_class to replace __setscheduler_class().
Fixes: f0e1a0643a59 ("sched_ext: Implement BPF extensible scheduler class") Cc: stable@vger.kernel.org # v6.12+ Signed-off-by: Zqiang qiang.zhang@linux.dev Reviewed-by: Andrea Righi arighi@nvidia.com Signed-off-by: Tejun Heo tj@kernel.org [ Adjust context ] Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/sched/ext.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-)
--- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -210,6 +210,14 @@ static struct scx_dispatch_q *find_user_ return rhashtable_lookup_fast(&sch->dsq_hash, &dsq_id, dsq_hash_params); }
+static const struct sched_class *scx_setscheduler_class(struct task_struct *p) +{ + if (p->sched_class == &stop_sched_class) + return &stop_sched_class; + + return __setscheduler_class(p->policy, p->prio); +} + /* * scx_kf_mask enforcement. Some kfuncs can only be called from specific SCX * ops. When invoking SCX ops, SCX_CALL_OP[_RET]() should be used to indicate @@ -3994,8 +4002,7 @@ static void scx_disable_workfn(struct kt scx_task_iter_start(&sti); while ((p = scx_task_iter_next_locked(&sti))) { const struct sched_class *old_class = p->sched_class; - const struct sched_class *new_class = - __setscheduler_class(p->policy, p->prio); + const struct sched_class *new_class = scx_setscheduler_class(p); struct sched_enq_and_set_ctx ctx;
if (old_class != new_class && p->se.sched_delayed) @@ -4779,8 +4786,7 @@ static int scx_enable(struct sched_ext_o scx_task_iter_start(&sti); while ((p = scx_task_iter_next_locked(&sti))) { const struct sched_class *old_class = p->sched_class; - const struct sched_class *new_class = - __setscheduler_class(p->policy, p->prio); + const struct sched_class *new_class = scx_setscheduler_class(p); struct sched_enq_and_set_ctx ctx;
if (!tryget_task_struct(p))