linux-kernel - Re: [PATCH v2] coresight: Fix possible deadlock in coresight_panic

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Message-ID: <aMP95WqHyIQq8TcS@e129823.arm.com>
Date: Fri, 12 Sep 2025 12:03:01 +0100
From: Yeoreum Yun <yeoreum.yun@....com>
To: Leo Yan <leo.yan@....com>
Cc: Sean Anderson <sean.anderson@...ux.dev>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Mike Leach <mike.leach@...aro.org>,
	Linu Cherian <lcherian@...vell.com>,
	James Clark <james.clark@...aro.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] coresight: Fix possible deadlock in coresight_panic_cb

Hi,

> Hi Sean,
>
> On Thu, Sep 11, 2025 at 11:33:15AM -0400, Sean Anderson wrote:
> > coresight_panic_cb is called with interrupts disabled during panics.
> > However, bus_for_each_dev calls bus_to_subsys which takes
> > bus_kset->list_lock without disabling IRQs. This will cause a deadlock
> > if a panic occurs while one of the other coresight functions that uses
> > bus_for_each_dev is running.
>
> The decription is a bit misleading. Even when IRQ is disabled, if an
> exception happens, a CPU still can be trapped for handling kernel panic.
>
> > Maintain a separate list of coresight devices to access during a panic.
>
> Rather than maintaining a separate list and introducing a new spinlock,
> I would argue if we can simply register panic notifier in TMC ETR and
> ETF drviers (see tmc_panic_sync_etr() and tmc_panic_sync_etf()).
>
> If there is no dependency between CoreSight modules in panic sync flow,
> it is not necessary to maintain list (and lock) for these modules.

+1 for this.
and using the spinlock in the panic_cb doesn't work on PREEMPT_RT side.

Thanks.

--
Sincerely,
Yeoreum Yun