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

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Date:   Thu, 9 Dec 2021 19:22:59 +0530
From:   Kashyap Desai <kashyap.desai@...adcom.com>
To:     Jens Axboe <axboe@...nel.dk>, John Garry <john.garry@...wei.com>
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

+ 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 ?

Kashyap

> >
> >
>
> Applied, thanks!
>
> [1/1] blk-mq: Fix blk_mq_tagset_busy_iter() for shared tags
>       commit: 0994c64eb4159ba019e7fedc7ba0dd6a69235b40
>
> Best regards,
> --
> Jens Axboe
>

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