On 2024-08-06 12:27:03 [+0200], Jerome Brunet wrote:
With PREEMPT_RT enabled, spinlocks become preemptible.
With PREEMPT_RT enabled a spinlock_t becomes a sleeping lock.
This is usually not a problem with spinlocks used in IRQ context since IRQ handlers get threaded. However, if IRQF_ONESHOT is set, the upper half of a threaded irq handler won't be threaded and this causes scheduling problems if spinlocks are used in the upper half, like with regmap when '.fast_io' is set.
… However, if IRQF_ONESHOT is set, the primary handler won't be force-threaded and runs always in hardirq context. This is a problem because spinlock_t requires a preemptible context on PREEMPT_RT.
In this particular instance, it is actually better to do everything in the bottom half and it solves the problem with PREEMPT_RT.
threaded handler
The term "bottom half" is usually used with softirq. The IRQ part has a primary handler and a threaded handler.
Reported-by: Arseniy Krasnov avkrasnov@salutedevices.com Closes: https://lore.kernel.org/linux-amlogic/20240729131652.3012327-1-avkrasnov@sal... Suggested-by: Sebastian Andrzej Siewior bigeasy@linutronix.de Fixes: b11d26660dff ("ASoC: meson: axg-fifo: use threaded irq to check periods") Signed-off-by: Jerome Brunet jbrunet@baylibre.com
sound/soc/meson/axg-fifo.c | 26 ++++++++++---------------- 1 file changed, 10 insertions(+), 16 deletions(-)
diff --git a/sound/soc/meson/axg-fifo.c b/sound/soc/meson/axg-fifo.c index 7e6090af720b..d0d05fa44d66 100644 --- a/sound/soc/meson/axg-fifo.c +++ b/sound/soc/meson/axg-fifo.c @@ -251,8 +244,9 @@ int axg_fifo_pcm_open(struct snd_soc_component *component, if (ret) return ret;
- ret = request_threaded_irq(fifo->irq, axg_fifo_pcm_irq_block,
axg_fifo_pcm_irq_block_thread,
- /* Use the bottom half of a threaded irq with non-atomic links */
This requests only a threaded handler. There is no "bottom half of a threaded IRQ".
- ret = request_threaded_irq(fifo->irq, NULL,
axg_fifo_pcm_irq_block, IRQF_ONESHOT, dev_name(dev), ss);
Sebastian