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Message-ID: <a37f9c82-9f25-c5ba-f941-1cedf8c10187@kernel.org>
Date:   Tue, 29 Nov 2022 09:33:45 -0700
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Subject: Re: [PATCH net] net: Add a gfp_t parameter in ip_fib_metrics_init to
 support atomic context
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To:     Duoming Zhou <duoming@zju.edu.cn>, linux-kernel@vger.kernel.org
Cc:     davem@davemloft.net, yoshfuji@linux-ipv6.org, edumazet@google.com,
        kuba@kernel.org, pabeni@redhat.com, netdev@vger.kernel.org
References: <20221129055317.53788-1-duoming@zju.edu.cn>
From:   David Ahern <dsahern@kernel.org>
In-Reply-To: <20221129055317.53788-1-duoming@zju.edu.cn>
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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
>