From 0b8f35aea8faf318e8a324ba2eed42fe3f8fc929 Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Wed, 6 Oct 2021 13:18:50 +0200 Subject: [PATCH 053/158] irq_work: Allow irq_work_sync() to sleep if irq_work() no IRQ support. irq_work() triggers instantly an interrupt if supported by the architecture. Otherwise the work will be processed on the next timer tick. In worst case irq_work_sync() could spin up to a jiffy. irq_work_sync() is usually used in tear down context which is fully preemptible. Based on review irq_work_sync() is invoked from preemptible context and there is one waiter at a time. This qualifies it to use rcuwait for synchronisation. Let irq_work_sync() synchronize with rcuwait if the architecture processes irqwork via the timer tick. Signed-off-by: Sebastian Andrzej Siewior Link: https://lore.kernel.org/r/20211006111852.1514359-3-bigeasy@linutronix.de --- include/linux/irq_work.h | 3 +++ kernel/irq_work.c | 10 ++++++++++ 2 files changed, 13 insertions(+) Index: linux-5.15.19-rt29/include/linux/irq_work.h =================================================================== --- linux-5.15.19-rt29.orig/include/linux/irq_work.h +++ linux-5.15.19-rt29/include/linux/irq_work.h @@ -3,6 +3,7 @@ #define _LINUX_IRQ_WORK_H #include +#include /* * An entry can be in one of four states: @@ -16,11 +17,13 @@ struct irq_work { struct __call_single_node node; void (*func)(struct irq_work *); + struct rcuwait irqwait; }; #define __IRQ_WORK_INIT(_func, _flags) (struct irq_work){ \ .node = { .u_flags = (_flags), }, \ .func = (_func), \ + .irqwait = __RCUWAIT_INITIALIZER(irqwait), \ } #define IRQ_WORK_INIT(_func) __IRQ_WORK_INIT(_func, 0) Index: linux-5.15.19-rt29/kernel/irq_work.c =================================================================== --- linux-5.15.19-rt29.orig/kernel/irq_work.c +++ linux-5.15.19-rt29/kernel/irq_work.c @@ -160,6 +160,9 @@ void irq_work_single(void *arg) * else claimed it meanwhile. */ (void)atomic_cmpxchg(&work->node.a_flags, flags, flags & ~IRQ_WORK_BUSY); + + if (!arch_irq_work_has_interrupt()) + rcuwait_wake_up(&work->irqwait); } static void irq_work_run_list(struct llist_head *list) @@ -204,6 +207,13 @@ void irq_work_tick(void) void irq_work_sync(struct irq_work *work) { lockdep_assert_irqs_enabled(); + might_sleep(); + + if (!arch_irq_work_has_interrupt()) { + rcuwait_wait_event(&work->irqwait, !irq_work_is_busy(work), + TASK_UNINTERRUPTIBLE); + return; + } while (irq_work_is_busy(work)) cpu_relax();