[PATCH v5 3/3] coresight: Fix possible deadlock in coresight_panic_cb

[Leo Yan]

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 at linux.dev>

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