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Date:   Mon, 07 Sep 2020 15:13:19 +0300
From:   Vlad Buslov <vlad@...lov.dev>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org,
        syzbot+80e32b5d1f9923f8ace6@...kaller.appspotmail.com,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Vlad Buslov <vladbu@...lanox.com>,
        Jiri Pirko <jiri@...nulli.us>
Subject: Re: [Patch net] act_ife: load meta modules before tcf_idr_check_alloc()


On Sat 05 Sep 2020 at 08:14, Jakub Kicinski <kuba@...nel.org> wrote:
> On Thu,  3 Sep 2020 19:10:11 -0700 Cong Wang wrote:
>> The following deadlock scenario is triggered by syzbot:
>> 
>> Thread A:				Thread B:
>> tcf_idr_check_alloc()
>> ...
>> populate_metalist()
>>   rtnl_unlock()
>> 					rtnl_lock()
>> 					...
>>   request_module()			tcf_idr_check_alloc()
>>   rtnl_lock()
>> 
>> At this point, thread A is waiting for thread B to release RTNL
>> lock, while thread B is waiting for thread A to commit the IDR
>> change with tcf_idr_insert() later.
>> 
>> Break this deadlock situation by preloading ife modules earlier,
>> before tcf_idr_check_alloc(), this is fine because we only need
>> to load modules we need potentially.
>> 
>> Reported-and-tested-by: syzbot+80e32b5d1f9923f8ace6@...kaller.appspotmail.com
>> Fixes: 0190c1d452a9 ("net: sched: atomically check-allocate action")
>> Cc: Jamal Hadi Salim <jhs@...atatu.com>
>> Cc: Vlad Buslov <vladbu@...lanox.com>
>
> Vlad, it'd have been nice to see your review tag here.

Reviewed. Sorry for the delay.

>
>> Cc: Jiri Pirko <jiri@...nulli.us>
>> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
>
> LGTM, applied and queued for stable, thank you Cong!

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