On Tue, Jul 01, 2008 at 07:02:54PM +0400, Anton Vorontsov wrote: [...] > Signed-off-by: Anton Vorontsov <avorontsov@xxxxxxxxxxxxx> > --- > > On Tue, Jul 01, 2008 at 02:43:53PM +0100, Alan Cox wrote: [...] > > 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, > 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@xxxxxxxxx irc://irc.freenode.net/bd2 -- 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
