6.17-stable review patch. If anyone has any objections, please let me know.
------------------
From: Tejun Heo tj@kernel.org
[ Upstream commit d452972858e5cfa4262320ab74fe8f016460b96f ]
The qmap dump operation was destructively consuming queue entries while displaying them. As dump can be triggered anytime, this can easily lead to stalls. Add a temporary dump_store queue and modify the dump logic to pop entries, display them, and then restore them back to the original queue. This allows dump operations to be performed without affecting the scheduler's queue state.
Note that if racing against new enqueues during dump, ordering can get mixed up, but this is acceptable for debugging purposes.
Acked-by: Andrea Righi arighi@nvidia.com Signed-off-by: Tejun Heo tj@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- tools/sched_ext/scx_qmap.bpf.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-)
diff --git a/tools/sched_ext/scx_qmap.bpf.c b/tools/sched_ext/scx_qmap.bpf.c index 69d877501cb72..cd50a94326e3a 100644 --- a/tools/sched_ext/scx_qmap.bpf.c +++ b/tools/sched_ext/scx_qmap.bpf.c @@ -56,7 +56,8 @@ struct qmap { queue1 SEC(".maps"), queue2 SEC(".maps"), queue3 SEC(".maps"), - queue4 SEC(".maps"); + queue4 SEC(".maps"), + dump_store SEC(".maps");
struct { __uint(type, BPF_MAP_TYPE_ARRAY_OF_MAPS); @@ -578,11 +579,26 @@ void BPF_STRUCT_OPS(qmap_dump, struct scx_dump_ctx *dctx) return;
scx_bpf_dump("QMAP FIFO[%d]:", i); + + /* + * Dump can be invoked anytime and there is no way to iterate in + * a non-destructive way. Pop and store in dump_store and then + * restore afterwards. If racing against new enqueues, ordering + * can get mixed up. + */ bpf_repeat(4096) { if (bpf_map_pop_elem(fifo, &pid)) break; + bpf_map_push_elem(&dump_store, &pid, 0); scx_bpf_dump(" %d", pid); } + + bpf_repeat(4096) { + if (bpf_map_pop_elem(&dump_store, &pid)) + break; + bpf_map_push_elem(fifo, &pid, 0); + } + scx_bpf_dump("\n"); } }