linux-kernel - Re: [PATCH RFC v2 03/18] scsi: core: Implement reserved command handling

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 20 Jun 2022 11:05:43 +0200
From:   Christoph Hellwig <hch@....de>
To:     Damien Le Moal <damien.lemoal@...nsource.wdc.com>
Cc:     Hannes Reinecke <hare@...e.de>, John Garry <john.garry@...wei.com>,
        Bart Van Assche <bvanassche@....org>, axboe@...nel.dk,
        jejb@...ux.ibm.com, martin.petersen@...cle.com, brking@...ibm.com,
        hch@....de, linux-block@...r.kernel.org, linux-ide@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
        chenxiang66@...ilicon.com
Subject: Re: [PATCH RFC v2 03/18] scsi: core: Implement reserved command
 handling

On Mon, Jun 20, 2022 at 06:02:30PM +0900, Damien Le Moal wrote:
> So reserving a tag/req to be able to do NCQ at the cost of max qd being 31
> works for that. We could keep max qd at 32 by creating one more "fake" tag
> and having a request for it, that is, having the fake tag visible to the
> block layer as a reserved tag, as John's series is doing, but for the
> reserved tags, we actually need to use an effective tag (qc->hw_tag) when
> issuing the commands. And for that, we can reuse the tag of one of the
> failed commands.

Take a look at the magic flush request in blk-flush.c, which is
preallocated but borrows a tag from the request that wants a pre- or
post-flush.  The logic is rather ugly, but maybe it might actually
become cleaner by generalizing it a bit.