linux-kernel - Re: [RESEND PATCH] nvme-fabrics: use reserved tag for reg read/write command

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Message-ID: <Zlo44PRN94sfQAoI@kbusch-mbp.dhcp.thefacebook.com>
Date: Fri, 31 May 2024 14:53:52 -0600
From: Keith Busch <kbusch@...nel.org>
To: "brookxu.cn" <brookxu.cn@...il.com>
Cc: axboe@...nel.dk, hch@....de, sagi@...mberg.me, kch@...dia.com,
	linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH] nvme-fabrics: use reserved tag for reg read/write
 command

On Fri, May 31, 2024 at 05:24:21PM +0800, brookxu.cn wrote:
> From: Chunguang Xu <chunguang.xu@...pee.com>
> 
> In some scenarios, if too many commands are issued by nvme command in
> the same time by user tasks, this may exhaust all tags of admin_q. If
> a reset (nvme reset or IO timeout) occurs before these commands finish,
> reconnect routine may fail to update nvme regs due to insufficient tags,
> which will cause kernel hang forever. In order to workaround this issue,
> maybe we can let reg_read32()/reg_read64()/reg_write32() use reserved
> tags. This maybe safe for nvmf:
> 
> 1. For the disable ctrl path,  we will not issue connect command
> 2. For the enable ctrl / fw activate path, since connect and reg_xx()
>    are called serially.
> 
> So the reserved tags may still be enough while reg_xx() use reserved tags.
> 
> Signed-off-by: Chunguang Xu <chunguang.xu@...pee.com>
> Reviewed-by: Sagi Grimberg <sagi@...mberg.me>
> Reviewed-by: Chaitanya Kulkarni <kch@...dia.com>

Thanks, applied to nvme-6.10.