From: Jakub Kicinski <kuba@kernel.org>
To: Jeongjun Park <aha310510@gmail.com>
Cc: richardcochran@gmail.com, andrew+netdev@lunn.ch,
davem@davemloft.net, edumazet@google.com, pabeni@redhat.com,
yangbo.lu@nxp.com, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org,
syzbot+7cfb66a237c4a5fb22ad@syzkaller.appspotmail.com
Subject: Re: [PATCH net] ptp: prevent possible ABBA deadlock in ptp_clock_freerun()
Date: Mon, 7 Jul 2025 17:11:18 -0700 [thread overview]
Message-ID: <20250707171118.55fc88cc@kernel.org> (raw)
In-Reply-To: <20250705145031.140571-1-aha310510@gmail.com>
On Sat, 5 Jul 2025 23:50:31 +0900 Jeongjun Park wrote:
> ABBA deadlock occurs in the following scenario:
>
> CPU0 CPU1
> ---- ----
> n_vclocks_store()
> lock(&ptp->n_vclocks_mux) [1]
> pc_clock_adjtime()
> lock(&clk->rwsem) [2]
> ...
> ptp_clock_freerun()
> ptp_vclock_in_use()
> lock(&ptp->n_vclocks_mux) [3]
> ptp_clock_unregister()
> posix_clock_unregister()
> lock(&clk->rwsem) [4]
>
> To solve this with minimal patches, we should change ptp_clock_freerun()
> to briefly release the read lock before calling ptp_vclock_in_use() and
> then re-lock it when we're done.
Dropping locks randomly is very rarely the correct fix.
Either way - you forgot to CC Vladimir, again.
--
pw-bot: cr
next prev parent reply other threads:[~2025-07-08 0:11 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-07-05 14:50 [PATCH net] ptp: prevent possible ABBA deadlock in ptp_clock_freerun() Jeongjun Park
2025-07-08 0:11 ` Jakub Kicinski [this message]
2025-07-16 5:12 ` Jeongjun Park
2025-07-16 21:24 ` Jakub Kicinski
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