8250's initialization routines relies on the fact that _irqsave spinlock will disable local hardirqs, so that the driver can issue IRQ-triggering operations before registering the port in the IRQ chain. With RT kernels and preemptable hardirqs this isn't true, _irqsave spinlock does not disable local hardirqs, and this causes following trace: $ cat /dev/ttyS1 irq 42: nobody cared (try booting with the "irqpoll" option) Call Trace: [C0475EB0] [C0008A98] show_stack+0x4c/0x1ac (unreliable) [C0475EF0] [C004BBD4] __report_bad_irq+0x34/0xb8 [C0475F10] [C004BD38] note_interrupt+0xe0/0x308 [C0475F50] [C004B09C] thread_simple_irq+0xdc/0x104 [C0475F70] [C004B3FC] do_irqd+0x338/0x3c8 [C0475FC0] [C00398E0] kthread+0xf8/0x100 [C0475FF0] [C0011FE0] original_kernel_thread+0x44/0x60 handlers: [<c02112c4>] (serial8250_interrupt+0x0/0x138) Disabling IRQ #42 After this, all serial ports on the given IRQ are non-functional. To fix the issue we should explicitly disable shared IRQ before issuing any IRQ-triggering operations. I also changed spin_lock_irqsave to the ordinary spin_lock, since it seems to be safe: chain does not contain new port (yet), thus nobody will interfere us from the ISRs. Signed-off-by: Anton Vorontsov <avorontsov@xxxxxxxxxxxxx> --- drivers/serial/8250.c | 8 ++++++-- 1 files changed, 6 insertions(+), 2 deletions(-) diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c index 76ccef7..702e0d3 100644 --- a/drivers/serial/8250.c +++ b/drivers/serial/8250.c @@ -1831,7 +1831,9 @@ static int serial8250_startup(struct uart_port *port) * the interrupt is enabled. Delays are necessary to * allow register changes to become visible. */ - spin_lock_irqsave(&up->port.lock, flags); + spin_lock(&up->port.lock); + if (up->port.flags & UPF_SHARE_IRQ) + disable_irq(up->port.irq); wait_for_xmitr(up, UART_LSR_THRE); serial_out_sync(up, UART_IER, UART_IER_THRI); @@ -1843,7 +1845,9 @@ static int serial8250_startup(struct uart_port *port) iir = serial_in(up, UART_IIR); serial_out(up, UART_IER, 0); - spin_unlock_irqrestore(&up->port.lock, flags); + if (up->port.flags & UPF_SHARE_IRQ) + enable_irq(up->port.irq); + spin_unlock(&up->port.lock); /* * If the interrupt is not reasserted, setup a timer to -- 1.5.5.4 -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
