From 57d12209790d3f006cd215d073780f3162d507c4 Mon Sep 17 00:00:00 2001 From: Radu Rendec Date: Sun, 5 Jul 2026 17:09:50 -0400 Subject: genirq: Remove unnecessary NULL check of the kstat_irqs field The kstat_irqs field of struct irq_desc is used to store a per-cpu count of interrupt events. It is initialized in init_desc(), along with all the other fields in struct irq_desc that need explicit initialization, and therefore it's always available (non-NULL) for any valid interrupt descriptor (with a caveat - see below). When CONFIG_SPARSE_IRQ is enabled, all interrupt descriptors are always allocated dynamically via alloc_desc(), which calls init_desc(), so in that case kstat_irqs is guaranteed to be non-NULL before a valid struct irq_desc pointer is even returned. By contrast, when CONFIG_SPARSE_IRQ is disabled, interrupt descriptors are allocated statically in the irq_desc[] array, and kstat_irqs is initialized implicitly to NULL. The per-cpu pointer is initialized only later, for all descriptors, via start_kernel() -> early_irq_init() -> init_desc(). The kstat_irqs field is used mostly for printing interrupt statistics (i.e. reading /proc/interrupts), and that cannot happen until much later, when user-space is fully initialized. So, there is no concern with that use case. The list below includes all functions where the NULL check is removed, along with a list of all possible call chains and/or a brief explanation of why it's safe to remove the NULL check in that case. * irq_desc_kstat_cpu() [include/linux/irqdesc.h] - All direct call sites use it for printing IRQ statistics. - Indirect call site: per_cpu_count_show() - also used for printing interruptstatistics. * kstat_irqs_cpu() [kernel/irq/irqdesc.c] - Called by sun3_int7() and sun3_int5() [arch/m68k/sun3/sun3ints.c] These are interrupt handlers and cannot be called until their corresponding interrupts are initialized in sun3_init_IRQ(). The call chain leading to that is: start_kernel() -> init_IRQ() [arch/m68k/kernel/ints.c] -> mach_init_IRQ = sun3_init_IRQ() The init_IRQ() call happens right *after* the early_irq_init() call, which means the descriptors are already fully initialized by the time the interrupt handlers are even registered. - Called by show_interrupts() [arch/s390/kernel/irq.c] - used for printing interrupt statistics. * kstat_irqs() [kernel/irq/irqdesc.c] The only possible call chain is via fs/proc/stat.c: stat_open() -> show_stat() -> show_all_irqs() -> kstat_irqs_usr() -> kstat_irqs() It is used for printing interrupt statistics. * kstat_snapshot_irqs() The only possible call chain is via kernel/watchdog.c: watchdog_timer_fn() -> is_softlockup() -> start_counting_irqs() -> kstat_snapshot_irqs() The watchdog timer cannot fire early, before early_irq_init(). * kstat_get_irq_since_snapshot() The only possible call chain is via kernel/watchdog.c: watchdog_timer_fn() -> report_cpu_status() -> print_irq_counts() -> kstat_get_irq_since_snapshot() The watchdog timer cannot fire early, before early_irq_init(). Signed-off-by: Radu Rendec Signed-off-by: Thomas Gleixner Link: https://patch.msgid.link/20260705210951.2717741-2-radu@rendec.net --- include/linux/irqdesc.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include/linux') diff --git a/include/linux/irqdesc.h b/include/linux/irqdesc.h index 8080db17c1b1..779d6023c5c2 100644 --- a/include/linux/irqdesc.h +++ b/include/linux/irqdesc.h @@ -146,7 +146,7 @@ extern struct irq_desc irq_desc[NR_IRQS]; static inline unsigned int irq_desc_kstat_cpu(struct irq_desc *desc, unsigned int cpu) { - return desc->kstat_irqs ? per_cpu(desc->kstat_irqs->cnt, cpu) : 0; + return per_cpu(desc->kstat_irqs->cnt, cpu); } static inline struct irq_desc *irq_data_to_desc(struct irq_data *data) -- cgit v1.2.3