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Subject: Re: [PATCH] scsi: ufs: Fix proper API to send HPB pre-request
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From:   Bart Van Assche <bvanassche@acm.org>
Message-ID: <42ca5f60-4c57-ade1-5fb7-be935ac4ccce@acm.org>
Date:   Thu, 28 Oct 2021 13:04:06 -0700
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On 10/28/21 12:12 PM, James Bottomley wrote:
> I think the deadlock is triggered if the system is down to its last
> reserved request on the memory clearing device and the next entry in
> the queue for this device is one which does a fanout so we can't
> service it with the single reserved request we have left for the
> purposes of making forward progress.  Sending it back doesn't help,
> assuming this is the only memory clearing path, because retrying it
> won't help ... we have to succeed with a request on this path to move
> forward with clearing memory.
> 
> I think this problem could be solved by processing the WRITE BUFFER and
> the request serially by hijacking the request sent down, but we can't
> solve it if we try to allocate a new request.

Hi James,

How about fixing the abuse of blk_insert_cloned_request() in the UFS HPB
before the v5.16 SCSI pull request is sent to Linus and implementing the
proposal from your email at a later time? I'm proposing to defer further
UFS HPB rework since the issue described above only affects UFS HPB users
and does not obstruct maintenance or refactoring of the block layer core.

Thanks,

Bart.