linux-kernel - Re: [PATCH net-next] 6pack: drop redundant locking and refcounting

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Message-ID: <aNJINihPJop9s7IR@stanley.mountain>
Date: Tue, 23 Sep 2025 10:11:50 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Qingfang Deng <dqfext@...il.com>
Cc: Andreas Koensgen <ajk@...nets.uni-bremen.de>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	linux-hams@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	syzbot+5fd749c74105b0e1b302@...kaller.appspotmail.com
Subject: Re: [PATCH net-next] 6pack: drop redundant locking and refcounting

On Tue, Sep 23, 2025 at 02:07:06PM +0800, Qingfang Deng wrote:
> The TTY layer already serializes line discipline operations with
> tty->ldisc_sem, so the extra disc_data_lock and refcnt in 6pack
> are unnecessary.
> 
> Removing them simplifies the code and also resolves a lockdep warning
> reported by syzbot. The warning did not indicate a real deadlock, since
> the write-side lock was only taken in process context with hardirqs
> disabled.
> 
> Reported-by: syzbot+5fd749c74105b0e1b302@...kaller.appspotmail.com
> Signed-off-by: Qingfang Deng <dqfext@...il.com>

checkpatch says:

WARNING: Reported-by: should be immediately followed by Closes: with a URL to the report

Which is relevant here because Google has apparently deleted their
search button and is only displaying the AI button.  "The email address
syzbot+5fd749c74105b0e1b302@...kaller.appspotmail.com is an automated
sender used by ..."  Thanks, AI!  I can still press enter to do a Google
search but there are no results with syzbot ID.

I can't find a search button on the syzbot website.

Ah.  Let's check lore.  Hooray!  How did we ever survive before lore?
https://lore.kernel.org/all/000000000000e8231f0601095c8e@google.com/

Please add the Closes tag and resend.  Otherwise it looks good.  Thanks!

This code was copy and pasted from drivers/net/ppp/ppp_synctty.c btw so
that's a similar thing if anyone wants to fix that.

KTODO: remove sp_get/put() from ppp_synctty.c

regards,
dan carpenter