| Message ID | 20210317143859.513307808@linutronix.de |
|---|---|
| State | New |
| Headers | show |
| Series | [1/1] genirq: Disable interrupts for force threaded handlers | expand |
On Wed, Mar 17 2021 at 15:48, Sebastian Andrzej Siewior wrote: > On 2021-03-17 15:38:52 [+0100], Thomas Gleixner wrote: >> thread(irq_A) >> irq_handler(A) >> spin_lock(&foo->lock); >> >> interrupt(irq_B) >> irq_handler(B) >> spin_lock(&foo->lock); > > It will not because both threads will wake_up(thread). It is an issue if > - if &foo->lock is shared between a hrtimer and threaded-IRQ > - if &foo->lock is shared between a non-threaded and thread-IRQ > - if &foo->lock is shared between a printk() in hardirq context and > thread-IRQ as I learned today. That's the point and it's entirely clear from the above: A is thread context and B is hard interrupt context and if the lock is shared then it's busted. Otherwise we would not have this discussion at all.
On 2021-03-17 17:23:39 [+0100], Johan Hovold wrote: > > > thread(irq_A) > > > irq_handler(A) > > > spin_lock(&foo->lock); > > > > > > interrupt(irq_B) > > > irq_handler(B) > > > spin_lock(&foo->lock); > > > > It will not because both threads will wake_up(thread). > > Note that the above says "interrupt(irq_B)" suggesting it's a > non-threaded interrupt unlike irq_A. I missed that bit, thanks. Sebastian
--- a/kernel/irq/manage.c +++ b/kernel/irq/manage.c @@ -1142,11 +1142,15 @@ irq_forced_thread_fn(struct irq_desc *de irqreturn_t ret; local_bh_disable(); + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + 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)) + local_irq_enable(); local_bh_enable(); return ret; }
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> Cc: Eric Dumazet <edumazet@google.com> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: netdev <netdev@vger.kernel.org> Cc: "David S. Miller" <davem@davemloft.net> Cc: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Andy Shevchenko <andy.shevchenko@gmail.com> CC: Peter Zijlstra <peterz@infradead.org> Cc: linux-serial@vger.kernel.org Cc: netdev <netdev@vger.kernel.org> --- kernel/irq/manage.c | 4 ++++ 1 file changed, 4 insertions(+)