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Date: Thu, 25 Sep 2025 17:22:52 +0100
From: Leo Yan <leo.yan@arm.com>
To: Sean Anderson <sean.anderson@linux.dev>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>, coresight@lists.linaro.org,
	linux-arm-kernel@lists.infradead.org,
	Yeoreum Yun <yeoreum.yun@arm.com>,
	Linu Cherian <lcherian@marvell.com>,
	Mike Leach <mike.leach@linaro.org>, linux-kernel@vger.kernel.org,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	James Clark <james.clark@linaro.org>
Subject: Re: [PATCH v5 3/3] coresight: Fix possible deadlock in
 coresight_panic_cb
Message-ID: <20250925162252.GE7985@e132581.arm.com>
References: <20250925150342.1845615-1-sean.anderson@linux.dev>
 <20250925150342.1845615-4-sean.anderson@linux.dev>
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In-Reply-To: <20250925150342.1845615-4-sean.anderson@linux.dev>

On Thu, Sep 25, 2025 at 11:03:42AM -0400, Sean Anderson wrote:
> Panics can occur at any time, so taking locks may cause a deadlock (such
> as if the panicking CPU held the lock).  coresight_panic_cb uses
> bus_for_each_dev, but that calls bus_to_subsys which takes
> bus_kset->list_lock.
> 
> Instead of registering a single panic notifier and iterating over
> coresight devices, register a panic notifier for each coresight device
> that requires it (letting the atomic notifier list handle iteration).
> atomic_notifier_chain_unregister will just return -ENOENT if a notifier
> block isn't on the list, so it's safe to call when we haven't registered
> a notifier.
> 
> Fixes: 46006ceb5d02 ("coresight: core: Add provision for panic callbacks")
> Signed-off-by: Sean Anderson <sean.anderson@linux.dev>

Reviewed-by: Leo Yan <leo.yan@arm.com>