netdev - Re: [Patch net 1/2] net_sched: Prevent creation of classes with TC_H

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Message-ID: <20250311104835.GJ4159220@kernel.org>
Date: Tue, 11 Mar 2025 11:48:35 +0100
From: Simon Horman <horms@...nel.org>
To: Cong Wang <xiyou.wangcong@...il.com>
Cc: netdev@...r.kernel.org, jhs@...atatu.com, jiri@...nulli.us,
	mincho@...ori.io
Subject: Re: [Patch net 1/2] net_sched: Prevent creation of classes with
 TC_H_ROOT

On Thu, Mar 06, 2025 at 03:23:54PM -0800, Cong Wang wrote:
> The function qdisc_tree_reduce_backlog() uses TC_H_ROOT as a termination
> condition when traversing up the qdisc tree to update parent backlog
> counters. However, if a class is created with classid TC_H_ROOT, the
> traversal terminates prematurely at this class instead of reaching the
> actual root qdisc, causing parent statistics to be incorrectly maintained.
> In case of DRR, this could lead to a crash as reported by Mingi Cho.
> 
> Prevent the creation of any Qdisc class with classid TC_H_ROOT
> (0xFFFFFFFF) across all qdisc types, as suggested by Jamal.
> 
> Reported-by: Mingi Cho <mincho@...ori.io>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>

Hi Cong,

This change looks good to me.
But could we get a fixes tag?`

...