linux-kernel - Re: [PATCH] p9: trans_fd: Fix deadlock when connection cancel

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Message-ID: <m2bkrz7qc8.fsf@gmail.com>
Date:   Thu, 01 Sep 2022 10:55:36 +0800
From:   Schspa Shi <schspa@...il.com>
To:     asmadeus@...ewreck.org
Cc:     ericvh@...il.com, lucho@...kov.net, linux_oss@...debyte.com,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, v9fs-developer@...ts.sourceforge.net,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] p9: trans_fd: Fix deadlock when connection cancel


asmadeus@...ewreck.org writes:

> Schspa Shi wrote on Thu, Sep 01, 2022 at 02:09:50AM +0800:
>> To fix it, we can add extra reference counter to avoid deadlock, and
>> decrease it after we unlock the client->lock.
>
> Thanks for the patch!
>
> Unfortunately I already sent a slightly different version to the list,
> hidden in another syzbot thread, here:
> https://lkml.kernel.org/r/YvyD053bdbGE9xoo@codewreck.org
>
> (yes, sorry, not exactly somewhere I'd expect someone to find it... 9p
> hasn't had many contributors recently)
>
>
> Basically instead of taking an extra lock I just released the client
> lock before calling p9_client_cb, so it shouldn't hang anymore.
>
> We don't need the lock to call the cb as in p9_conn_cancel we already
> won't accept any new request and by this point the requests are in a
> local list that isn't shared anywhere.
>

Ok, thank you for pointing that out.

> If you have a test setup, would you mind testing my patch?
> That's the main reason I was delaying pushing it.
>

I have test it with my enviroment, it not hang anymore.

> Since you went out of your way to make this patch if you agree with my
> approach I don't mind adding your sign off or another mark of having
> worked on it.
>
> Thank you,

-- 
BRs
Schspa Shi