From: Sean Anderson <sean.anderson@linux.dev>
To: Yeoreum Yun <yeoreum.yun@arm.com>, Leo Yan <leo.yan@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>,
coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Mike Leach <mike.leach@linaro.org>,
Linu Cherian <lcherian@marvell.com>,
James Clark <james.clark@linaro.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] coresight: Fix possible deadlock in coresight_panic_cb
Date: Fri, 12 Sep 2025 10:38:44 -0400 [thread overview]
Message-ID: <6d833ea6-328f-4743-abfa-fb09b168849e@linux.dev> (raw)
In-Reply-To: <aMP95WqHyIQq8TcS@e129823.arm.com>
On 9/12/25 07:03, Yeoreum Yun wrote:
> 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.
Yeah, I was thinking about this as I was preparing v2 of this patch.
> +1 for this.
> and using the spinlock in the panic_cb doesn't work on PREEMPT_RT side.
What do you mean by this? I am using lockdep and it did not warn about this,
so I assume that on PREEMPT_RT IRQs remain enabled in this path.
--Sean
next prev parent reply other threads:[~2025-09-12 14:38 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-09-11 15:33 [PATCH v2] coresight: Fix possible deadlock in coresight_panic_cb Sean Anderson
2025-09-12 9:35 ` Leo Yan
2025-09-12 11:03 ` Yeoreum Yun
2025-09-12 14:38 ` Sean Anderson [this message]
2025-09-13 4:30 ` Yeoreum Yun
2025-09-15 14:32 ` Sean Anderson
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