linux-kernel - Re: [PATCH] blk-mq: Do not lookup ctx with invalid index

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Message-ID: <20210614113706.astexefgfo4tuejr@beryllium.lan>
Date:   Mon, 14 Jun 2021 13:37:06 +0200
From:   Daniel Wagner <dwagner@...e.de>
To:     linux-block@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH] blk-mq: Do not lookup ctx with invalid index

On Tue, Jun 08, 2021 at 08:33:39PM +0200, Daniel Wagner wrote:
> cpumask_first_and() returns >= nr_cpu_ids if the two provided masks do
> not share a common bit. Verify we get a valid value back from
> cpumask_first_and().

So I got feedback on this issue (but not on the patch itself yet). The
system starts with 16 virtual CPU cores and during the test 4 cores are
removed[1] and as soon there is an error on the storage side, the reset
code on the host ends up in this path and crashes. I still don't
understand why the CPU removal is not updating the CPU mask correctly
before we hit the reset path. I'll continue to investigate.

[1] echo 0 > /sys/devices/system/cpu/cpu#/online