netdev - Re: [PATCH net] net: Add a gfp_t parameter in ip_fib_metrics

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Date:   Tue, 29 Nov 2022 09:33:45 -0700
From:   David Ahern <dsahern@...nel.org>
To:     Duoming Zhou <duoming@....edu.cn>, linux-kernel@...r.kernel.org
Cc:     davem@...emloft.net, yoshfuji@...ux-ipv6.org, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com, netdev@...r.kernel.org
Subject: Re: [PATCH net] net: Add a gfp_t parameter in ip_fib_metrics_init to
 support atomic context

On 11/28/22 10:53 PM, Duoming Zhou wrote:
> The ip_fib_metrics_init() do not support atomic context, because it
> calls "kzalloc(..., GFP_KERNEL)". When ip_fib_metrics_init() is used
> in atomic context, the sleep-in-atomic-context bug will happen.

Did you actually hit this sleep-in-atomic-context bug or is it theory
based on code analysis?

> 
> For example, the neigh_proxy_process() is a timer handler that is
> used to process the proxy request that is timeout. But it could call
> ip_fib_metrics_init(). As a result, the can_block flag in ipv6_add_addr()
> and the gfp_flags in addrconf_f6i_alloc() and ip6_route_info_create()
> are useless. The process is shown below.
> 
>     (atomic context)
> neigh_proxy_process()
>   pndisc_redo()
>     ndisc_recv_ns()
>       addrconf_dad_failure()
>         ipv6_add_addr(..., bool can_block)
>           addrconf_f6i_alloc(..., gfp_t gfp_flags)

	cfg has fc_mx == NULL.

>             ip6_route_info_create(..., gfp_t gfp_flags)

	rt->fib6_metrics = ip_fib_metrics_init(net, cfg->fc_mx, cfg->fc_mx_len,
extack);

>               ip_fib_metrics_init()

        if (!fc_mx)
                return (struct dst_metrics *)&dst_default_metrics;


>                 kzalloc(..., GFP_KERNEL) //may sleep
>