From: Thomas Gleixner tglx@linutronix.de
commit 81e2073c175b887398e5bca6c004efa89983f58d upstream.
With interrupt force threading all device interrupt handlers are invoked from kernel threads. Contrary to hard interrupt context the invocation only disables bottom halfs, but not interrupts. This was an oversight back then because any code like this will have an issue:
thread(irq_A) irq_handler(A) spin_lock(&foo->lock);
interrupt(irq_B) irq_handler(B) spin_lock(&foo->lock);
This has been triggered with networking (NAPI vs. hrtimers) and console drivers where printk() happens from an interrupt which interrupted the force threaded handler.
Now people noticed and started to change the spin_lock() in the handler to spin_lock_irqsave() which affects performance or add IRQF_NOTHREAD to the interrupt request which in turn breaks RT.
Fix the root cause and not the symptom and disable interrupts before invoking the force threaded handler which preserves the regular semantics and the usefulness of the interrupt force threading as a general debugging tool.
For not RT this is not changing much, except that during the execution of the threaded handler interrupts are delayed until the handler returns. Vs. scheduling and softirq processing there is no difference.
For RT kernels there is no issue.
Fixes: 8d32a307e4fa ("genirq: Provide forced interrupt threading") Reported-by: Johan Hovold johan@kernel.org Signed-off-by: Thomas Gleixner tglx@linutronix.de Reviewed-by: Johan Hovold johan@kernel.org Acked-by: Sebastian Andrzej Siewior bigeasy@linutronix.de Link: https://lore.kernel.org/r/20210317143859.513307808@linutronix.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/irq/manage.c | 4 ++++ 1 file changed, 4 insertions(+)
--- a/kernel/irq/manage.c +++ b/kernel/irq/manage.c @@ -987,11 +987,15 @@ irq_forced_thread_fn(struct irq_desc *de irqreturn_t ret;
local_bh_disable(); + if (!IS_ENABLED(CONFIG_PREEMPT_RT_BASE)) + local_irq_disable(); ret = action->thread_fn(action->irq, action->dev_id); if (ret == IRQ_HANDLED) atomic_inc(&desc->threads_handled);
irq_finalize_oneshot(desc, action); + if (!IS_ENABLED(CONFIG_PREEMPT_RT_BASE)) + local_irq_enable(); local_bh_enable(); return ret; }