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

[Keith Busch]

On Fri, May 31, 2024 at 05:24:21PM +0800, brookxu.cn wrote:
> From: Chunguang Xu <chunguang.xu at shopee.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 at shopee.com>
> Reviewed-by: Sagi Grimberg <sagi at grimberg.me>
> Reviewed-by: Chaitanya Kulkarni <kch at nvidia.com>

Thanks, applied to nvme-6.10.