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[ Upstream commit b1bbd20f35e19774ea01989320495e09ac44fba3 ] Some triggers call led_trigger_event() from their activate() callback to initialize the brightness of the LED for which the trigger is being activated. In order for the LED's initial state to be set correctly this requires that the led_trigger_event() call uses the new version of trigger->led_cdevs, which has the new LED. AFAICT led_trigger_event() will always use the new version when it is running on the same CPU as where the list_add_tail_rcu() call was made, which is why the missing synchronize_rcu() has not lead to bug reports. But if activate() is pre-empted, sleeps or uses a worker then the led_trigger_event() call may run on another CPU which may still use the old trigger->led_cdevs list. Add a synchronize_rcu() call to ensure that any led_trigger_event() calls done from activate() always use the new list. Triggers using led_trigger_event() from their activate() callback are: net/bluetooth/leds.c, net/rfkill/core.c and drivers/tty/vt/keyboard.c. Signed-off-by: Hans de Goede <hdegoede@redhat.com> Link: https://lore.kernel.org/r/20240531120124.75662-1-hdegoede@redhat.com Signed-off-by: Lee Jones <lee@kernel.org> Stable-dep-of: ab477b766edd ("leds: triggers: Flush pending brightness before activating trigger") Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.