7.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Haris Okanovic commit e74798f2f8e1562f2bbd2fed8d81929eeef39ffc upstream. irq_seq_show() must be idempotent since it may be called multiple times to render the same record, e.g. when seq_file's buffer is exceeded. It emits the CPU header behind the one-shot print_header flag, which the first pass clears, so the header is lost with the discarded buffer. This can be seen on large systems, such as 8g.48xl (192 CPUs) and 8i.96xl (384 CPUs) AWS instance types: $ head -1 /proc/interrupts 9: 0 0 ... 0 GICv3 25 Level vgic Replace print_header with the position of the first record and include the header whenever that record is emitted. Fixes: 171cc0d9eed1 ("genirq/proc: Speed up /proc/interrupts iteration") Signed-off-by: Haris Okanovic Signed-off-by: Thomas Gleixner Tested-by: Michael Kelley Reviewed-by: Radu Rendec Link: https://patch.msgid.link/20260911-dev-harisokn-proc-interrupts-fix-b4-v1-1-f9ff208efcfa@amazon.com Signed-off-by: Greg Kroah-Hartman --- kernel/irq/proc.c | 24 +++++++++++++++++------- 1 file changed, 17 insertions(+), 7 deletions(-) --- a/kernel/irq/proc.c +++ b/kernel/irq/proc.c @@ -462,7 +462,7 @@ int __weak arch_show_interrupts(struct s static DEFINE_RAW_SPINLOCK(irq_proc_constraints_lock); static struct irq_proc_constraints { - bool print_header; + loff_t first_pos; unsigned int num_prec; unsigned int chip_width; } irq_proc_constraints __read_mostly = { @@ -543,14 +543,13 @@ static int irq_seq_show(struct seq_file struct irqaction *action; /* Print header for the first interrupt? */ - if (constr->print_header) { + if (p->index == constr->first_pos) { unsigned int cpu; seq_printf(p, "%*s", constr->num_prec + 8, ""); for_each_online_cpu(cpu) seq_printf(p, "CPU%-8d", cpu); seq_putc(p, '\n'); - constr->print_header = false; } if (desc == ARCH_PROC_IRQDESC) @@ -635,14 +634,25 @@ static void *irq_seq_next_desc(loff_t *p static void *irq_seq_start(struct seq_file *f, loff_t *pos) { - if (!*pos) { - struct irq_proc_constraints *constr = f->private; + struct irq_proc_constraints *constr = f->private; + bool first = !*pos; + void *ret; + if (first) { constr->num_prec = READ_ONCE(irq_proc_constraints.num_prec); constr->chip_width = READ_ONCE(irq_proc_constraints.chip_width); - constr->print_header = true; } - return irq_seq_next_desc(pos); + + ret = irq_seq_next_desc(pos); + + /* + * Record position of the first output record so that irq_seq_show() + * knows where to write the header. + */ + if (first) + constr->first_pos = *pos; + + return ret; } static void *irq_seq_next(struct seq_file *f, void *v, loff_t *pos)