Messages in this thread | | | Date | Fri, 28 Oct 2011 14:28:05 +0200 | From | Michael Thalmeier <> | Subject | Re: [PATCH] USB: g_serial: fix deadlock with PREEMPT_RT enabled |
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On 2011-10-28 14:16, Michael Thalmeier wrote:
> In commit 44a0c0190b500ee6bcfc0976fe540f65dee2cd67 unlocking of spin_locks has > been removed. This patch party restores this functionality. > > Signed-off-by: Michael Thalmeier <michael.thalmeier@hale.at> > --- > drivers/usb/gadget/u_serial.c | 9 +++++++++ > 1 files changed, 9 insertions(+), 0 deletions(-) > > diff --git a/drivers/usb/gadget/u_serial.c b/drivers/usb/gadget/u_serial.c > index 40f7716..a925b9e 100644 > --- a/drivers/usb/gadget/u_serial.c > +++ b/drivers/usb/gadget/u_serial.c > @@ -553,7 +553,16 @@ recycle: > * a workqueue, so we won't get callbacks and can hold port_lock > */ > if (tty && do_push) { > + /* > + * Drop the lock here since it might end up calling > + * gs_flush_chars, which takes the lock. > + */ > + spin_unlock_irq(&port->port_lock); > tty_flip_buffer_push(tty); > + spin_lock_irq(&port->port_lock); > + > + /* tty may have been closed */ > + tty = port->port_tty; > } > >
In the function tty_flip_buffer_push the PRREMPT_RT patch changes the behaviour. Most serial drivers (those that don't set low_latency) assume that work is only scheduled and not executed immediately in current context. This patch only fixes this driver but other serial drivers likely have similar problems.
Michael
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