linux-kernel - Re: [PATCH v2] blk-mq: Fix blk_mq_tagset_busy

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Message-ID: <3389cd7b-2934-8e82-b09a-a4fdb0f00ea3@huawei.com>
Date:   Thu, 9 Dec 2021 14:42:55 +0000
From:   John Garry <john.garry@...wei.com>
To:     Kashyap Desai <kashyap.desai@...adcom.com>,
        Jens Axboe <axboe@...nel.dk>
CC:     <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <hare@...e.de>, <ming.lei@...hat.com>, <linux-scsi@...r.kernel.org>
Subject: Re: [PATCH v2] blk-mq: Fix blk_mq_tagset_busy_iter() for shared tags

On 09/12/2021 13:52, Kashyap Desai wrote:
> + scsi mailing list
> 
>> On Mon, 18 Oct 2021 17:41:23 +0800, John Garry wrote:
>>> Since it is now possible for a tagset to share a single set of tags,
>>> the iter function should not re-iter the tags for the count of #hw
>>> queues in that case. Rather it should just iter once.
> John - Recently we found issue of error hander thread never kicked off and
> this patch fix the issue.
> Without this patch, scsi error hander will not find correct host_busy
> counter.
> 
> Take one simple case. There is one IO outstanding and that is getting
> timedout.
> Now SML wants to wake up EH thread only if, below condition met
> "scsi_host_busy(shost) == shost->host_failed"
> 
> Without this patch, shared host tag enabled meagaraid_sas driver will find
> host_busy = actual outstanding * nr_hw_queues.
> Error handler thread will never be kicked-off.
> 
> This patch is mandatory for fixing shared host tag feature and require to be
> part of stable kernel.
> 
> Do you need more data for posting to stable kernel ?

To be clear, are you saying that you see the issue which patch "blk-mq: 
Fix blk_mq_tagset_busy_iter() for shared tags" fixes before v5.16-rc?

This patch (now commit 0994c64eb415) and the commit which it is supposed 
to fix, e155b0c238b2, will only be in v5.16, so I don't see anything 
which is needed in stable.

Thanks,
John