From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Thalmeier Subject: Re: [PATCH] USB: g_serial: fix deadlock with PREEMPT_RT enabled Date: Fri, 28 Oct 2011 14:28:05 +0200 Message-ID: <4EAA9FD5.4070202@hale.at> References: <1319804185-18559-1-git-send-email-michael.thalmeier@hale.at> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: rt , lkml , Michael Thalmeier To: Thomas Gleixner Return-path: Received: from mx11.lb01.inode.at ([62.99.145.13]:24351 "EHLO mx.inode.at" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753397Ab1J1M1I (ORCPT ); Fri, 28 Oct 2011 08:27:08 -0400 In-Reply-To: <1319804185-18559-1-git-send-email-michael.thalmeier@hale.at> Sender: linux-rt-users-owner@vger.kernel.org List-ID: 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 > --- > 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 -- Scanned by MailScanner.