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

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Message-ID: <2739602.9NfmOOc9RC@silver>
Date:   Thu, 01 Sep 2022 17:27:53 +0200
From:   Christian Schoenebeck <linux_oss@...debyte.com>
To:     asmadeus@...ewreck.org, Schspa Shi <schspa@...il.com>
Cc:     ericvh@...il.com, lucho@...kov.net, 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

On Donnerstag, 1. September 2022 04:55:36 CEST Schspa Shi wrote:
> 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.

Are you fine with that Dominique, or do you want me to test your linked patch 
as well?

You can also explicitly tell me if you need something to be reviewed/tested.

> > 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,