[PATCH] x86/apic/msi: check interupt context before reporting warning

[Yongxin Liu]

Affinity change can happen in both interrupt context and non-interrupt
context. The paranoia check for interrupt target cpu is not always true
in non-interrupt context.

For example:
  Set affinity for irq to CPU#7
  $ echo 80 > /proc/irq/default_smp_affinity

  Open serial port on different CPU.
  $taskset -c 4 agetty -L 115200 ttyS1

Will triger the following warning.

  WARNING: CPU: 4 PID: 765 at arch/x86/kernel/apic/msi.c:75 msi_set_affinity+0x16f/0x190
  Call Trace:
   irq_do_set_affinity+0x57/0x1b0
   irq_setup_affinity+0x136/0x190
   irq_startup+0xaf/0xf0
   __setup_irq+0x745/0x7e0
   ? kmem_cache_alloc_trace+0x2b5/0x450
   request_threaded_irq+0x110/0x180
   univ8250_setup_irq+0x1e2/0x220
   serial8250_do_startup+0x481/0x760
   serial8250_startup+0x1e/0x20
   uart_startup.part.22+0xf8/0x260
   uart_port_activate+0x41/0x60
   tty_port_open+0x82/0xd0
   ? _raw_spin_unlock+0x16/0x30
   uart_open+0x1e/0x30
   tty_open+0x100/0x4d0
   ? cdev_purge+0x60/0x60
   chrdev_open+0xa3/0x1c0
   ? cdev_put.part.3+0x20/0x20
   do_dentry_open+0x21f/0x380
   vfs_open+0x2f/0x40
   path_openat+0xd67/0xf60
   ? page_add_file_rmap+0xad/0x140
   ? do_set_pte+0xd7/0x210
   do_filp_open+0xc5/0x140
   do_sys_openat2+0x239/0x300
   ? do_sys_openat2+0x239/0x300
   do_sys_open+0x59/0x80
   __x64_sys_openat+0x20/0x30
   do_syscall_64+0x3f/0x90
   entry_SYSCALL_64_after_hwframe+0x44/0xae

With this patch, the warning is only reported in interrupt context and when
the target CPU is not local CPU.

Signed-off-by: Yongxin Liu <yongxin.liu@xxxxxxxxxxxxx>
---
 arch/x86/kernel/apic/msi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/apic/msi.c b/arch/x86/kernel/apic/msi.c
index 44ebe25e7703..c4c73f227eeb 100644
--- a/arch/x86/kernel/apic/msi.c
+++ b/arch/x86/kernel/apic/msi.c
@@ -72,7 +72,7 @@ msi_set_affinity(struct irq_data *irqd, const struct cpumask *mask, bool force)
 	 * Paranoia: Validate that the interrupt target is the local
 	 * CPU.
 	 */
-	if (WARN_ON_ONCE(cpu != smp_processor_id())) {
+	if (in_interrupt() && WARN_ON_ONCE(cpu != smp_processor_id())) {
 		irq_msi_update_msg(irqd, cfg);
 		return ret;
 	}
-- 
2.14.5