[PATCH v4 9/9] blk-mq: issue warning when offlining hctx with online isolcpus

Daniel Wagner
2024-12-19T15:57:12Z

When we offlining a hardware context which also serves isolcpus mapped
to it, any IO issued by the isolcpus will stall as there is nothing
which handles the interrupts etc.

This configuration/setup is not supported at this point thus just issue
a warning.

Signed-off-by: Daniel Wagner <wagi@kernel.org>
---
block/blk-mq.c | 43 ++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 42 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index de15c0c76f874a2a863b05a23e0f3dba20cb6488..f9af0f5dd6aac8da855777acf2ffc61128f15a74 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3619,6 +3619,45 @@ static bool blk_mq_hctx_has_requests(struct blk_mq_hw_ctx *hctx)
return data.has_rq;
}

+static void blk_mq_hctx_check_isolcpus_online(struct blk_mq_hw_ctx *hctx, unsigned int cpu)
+{
+ const struct cpumask *hk_mask;
+ int i;
+
+ if (!housekeeping_enabled(HK_TYPE_MANAGED_IRQ))
+ return;
+
+ hk_mask = housekeeping_cpumask(HK_TYPE_MANAGED_IRQ);
+
+ for (i = 0; i < hctx->nr_ctx; i++) {
+ struct blk_mq_ctx *ctx = hctx->ctxs[i];
+
+ if (ctx->cpu == cpu)
+ continue;
+
+ /*
+ * Check if this context has at least one online
+ * housekeeping CPU in this case the hardware context is
+ * usable.
+ */
+ if (cpumask_test_cpu(ctx->cpu, hk_mask) &&
+ cpu_online(ctx->cpu))
+ break;
+
+ /*
+ * The context doesn't have any online housekeeping CPUs
+ * but there might be an online isolated CPU mapped to
+ * it.
+ */
+ if (cpu_is_offline(ctx->cpu))
+ continue;
+
+ pr_warn("%s: offlining hctx%d but there is still an online isolcpu CPU %d mapped to it, IO stalls expected\n",
+ hctx->queue->disk->disk_name,
+ hctx->queue_num, ctx->cpu);
+ }
+}
+
static bool blk_mq_hctx_has_online_cpu(struct blk_mq_hw_ctx *hctx,
unsigned int this_cpu)
{
@@ -3638,8 +3677,10 @@ static bool blk_mq_hctx_has_online_cpu(struct blk_mq_hw_ctx *hctx,
continue;

/* this hctx has at least one online CPU */
- if (this_cpu != cpu)
+ if (this_cpu != cpu) {
+ blk_mq_hctx_check_isolcpus_online(hctx, this_cpu);
return true;
+ }
}

return false;

--
2.47.1