linux-kernel - [Question]Question about the possibility of a problem in blk_mq_complete

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Date:   Sat, 25 Dec 2021 00:10:09 +0900
From:   Manjong Lee <mj0123.lee@...sung.com>
To:     mj0123.lee@...sung.com, axboe@...nel.dk,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     seunghwan.hyun@...sung.com, sookwan7.kim@...sung.com,
        nanich.lee@...sung.com, woosung2.lee@...sung.com,
        yt0928.kim@...sung.com, junho89.kim@...sung.com,
        jisoo2146.oh@...sung.com
Subject: [Question]Question about the possibility of a problem in
 blk_mq_complete_remote.

Dear block layer developers.

While studying the block layer code, there is something I don't understand 
about the code.
It's hard to understand by myself. So I'd like to ask for your help.

I think the error can occur when the target cpu is changed to 
online -> offline during the ipi operation due to the request complete 
process below.

However, since the return value is not checked in the code,
it seems that a problem may occur.

So I wonder is this code the real problem or is there any other defense code?

Function path.

blk_mq_complete_request_remote
    blk_mq_complete_need_ipi  << Check if the cpu of rq is online
    blk_mq_complete_send_ipi  << Assume that the target cpu becomes offline here.
        smp_call_function_single_async 
            << send ipi to cpu and return -ENXIO if cpu is offline
               but it doesn't check the return value.