linux-kernel - Re: [PATCH net,v3] net: ppp: Fix deadlock caused by unsafe-irq lock in ap

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Message-Id: <20240422085801.140509-1-aha310510@gmail.com>
Date: Mon, 22 Apr 2024 17:58:01 +0900
From: Jeongjun Park <aha310510@...il.com>
To: jirislaby@...nel.org
Cc: davem@...emloft.net,
	edumazet@...gle.com,
	gregkh@...uxfoundation.org,
	kuba@...nel.org,
	linux-kernel@...r.kernel.org,
	linux-ppp@...r.kernel.org,
	netdev@...r.kernel.org,
	pabeni@...hat.com,
	syzbot+393d0ef63475d9bb1f16@...kaller.appspotmail.com,
	syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH net,v3] net: ppp: Fix deadlock caused by unsafe-irq lock in ap_get()

Jiri Slaby wrote:
> OK, but read_unlock_irq() is not the right way to do it. It would enable
> irqs unconditionally, so serial8250_tx_chars() would not thank you in
> the above call chain.
> 
> Plus the issues Jakub had with the patch.
> 
> And what about ppp_synctty?

Hmm... If the problem is the case of calling the function in 
serial8250_tx_chars(), I think it can be solved by continuing to use 
read_lock() in ppp_asynctty_wakeup() and getting the ap by not calling
ap_get().

If I do this, will I be able to apply the existing patch to ap_get()?

Thanks.