Re: [PATCH v2] serial: 8250: fix shared interrupts issues with SMP and RT kernels
From: Anton Vorontsov <hidden>
Date: 2008-07-09 19:29:59
Also in:
lkml
On Tue, Jul 01, 2008 at 07:02:54PM +0400, Anton Vorontsov wrote: [...]
Signed-off-by: Anton Vorontsov <redacted> --- On Tue, Jul 01, 2008 at 02:43:53PM +0100, Alan Cox wrote:
[...]
quoted
It looks correct to me except that you cannot use spin_lock/disable_irq in that way safely. You must always disable_irq before taking the lock, or prove it is safe and use disable_irq_nosync The reason: CPU#0 spin_lock_... [taken] CPU#1 IRQ CPU#1 spin_lock [waits] CPU#0 disable_irq (deadlock)This deadlock possibility is interesting by itself, thanks for mentioning it. But this can't happen here. IRQ will not grab the up->port.lock, because port isn't registered in the 8250 IRQ handling chain (yet).
Alan, are there any issues with the proof or the patch itself? Thanks,
quoted hunk ↗ jump to hunk
As for _nosync, probably this is good idea indeed, and should be safe AFAICS. 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..cad0c2d 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_nosync(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
-- Anton Vorontsov email: cbouatmailru@gmail.com irc://irc.freenode.net/bd2