Hi Sagi

Still can reproduce this issue with the change:

Thanks for validating Yi,

Would it be possible to test the following:
--
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 75336848f7a7..81ced3096433 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -444,6 +444,10 @@ struct request *blk_mq_alloc_request_hctx(struct
request_queue *q,
                 return ERR_PTR(-EXDEV);
         }
         cpu = cpumask_first_and(alloc_data.hctx->cpumask, cpu_online_mask);
+       if (cpu >= nr_cpu_ids) {
+               pr_warn("no online cpu for hctx %d\n", hctx_idx);
+               cpu = cpumask_first(alloc_data.hctx->cpumask);
+       }
         alloc_data.ctx = __blk_mq_get_ctx(q, cpu);

         rq = blk_mq_get_request(q, NULL, op, &alloc_data);
--
...


[  153.384977] BUG: unable to handle kernel paging request at
00003a9ed053bd48
[  153.393197] IP: blk_mq_get_request+0x23e/0x390

Also would it be possible to provide gdb output of:

l *(blk_mq_get_request+0x23e)

nvmf_connect_io_queue() is used in this way by asking blk-mq to allocate
request from one specific hw queue, but there may not be all online CPUs
mapped to this hw queue.

Yes, this is what I suspect..

And the following patchset may fail this kind of allocation and avoid
the kernel oops.

        https://marc.info/?l=linux-block&m=152318091025252&w=2

Thanks Ming,

But I don't want to fail the allocation, nvmf_connect_io_queue simply
needs a tag to issue the connect request, I much rather to take this
tag from an online cpu than failing it... We use this because we reserve
a tag per-queue for this, but in this case, I'd rather block until the
inflight tag complete than failing the connect.

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