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[ Upstream commit 3c7b30f704 ]
The BCM2835 pinctrl driver acquires a spinlock in its ->irq_enable,
->irq_disable and ->irq_set_type callbacks. Spinlocks become sleeping
locks with CONFIG_PREEMPT_RT_FULL=y, therefore invocation of one of the
callbacks in atomic context may cause a hard lockup if at least two GPIO
pins in the same bank are used as interrupts. The issue doesn't occur
with just a single interrupt pin per bank because the lock is never
contended. I'm experiencing such lockups with GPIO 8 and 28 used as
level-triggered interrupts, i.e. with ->irq_disable being invoked on
reception of every IRQ.
The critical section protected by the spinlock is very small (one bitop
and one RMW of an MMIO register), hence converting to a raw spinlock
seems a better trade-off than converting the driver to threaded IRQ
handling (which would increase latency to handle an interrupt).
Cc: Mathias Duckeck <m.duckeck@kunbus.de>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Acked-by: Julia Cartwright <julia@ni.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.