From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robin Murphy Subject: Re: [PATCH] serial/amba-pl011: Disable interrupts around TX softirq Date: Fri, 05 Jun 2015 19:03:42 +0100 Message-ID: <5571E47E.5020800@arm.com> References: <1433513267-24163-1-git-send-email-Dave.Martin@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1433513267-24163-1-git-send-email-Dave.Martin@arm.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Dave P Martin , "linux-serial@vger.kernel.org" , Greg Kroah-Hartman Cc: Russell King , =?ISO-8859-2?Q?Jakub_Kici=F1ski?= , Andre Przywara , Andrew Jackson , Graeme Gregory , popcorn mix , Jorge Ramirez-Ortiz , "linux-arm-kernel@lists.infradead.org" List-Id: linux-serial@vger.kernel.org On 05/06/15 15:07, Dave P Martin wrote: > pl011_tx_softirq() currently uses spin_{,un}lock(), which are not > sufficient to inhibit pl011_int() from being triggered by a local > IRQ and trying to re-take the same lock. This can lead to > deadlocks. > > This patch uses the _irq() locking variants instead to ensure that > pl011_int() handling for a given port is deferred until any > pl011_tx_softirq() work for that port is complete. > > Signed-off-by: Dave Martin > --- > > Another candidate for v4.1 if possible (sorry!) -- I thought this change > was already in, but it went astray when I was refactoring. > > This patch conflicts with tty-next like the previous patch, since it > fixes code that is removed by tty-next. The correct resolution for > the resulting merge conflict is to keep the code from tty-next. > > > I am not 100% certain yet whether some rare deadlocks that Robin is > seeing are caused by this issue, or whether this patch fixes them -- > he's testing atm. FWIW, I've been running Juno in a startup/shutdown loop with a very noisy systemd all afternoon and haven't hit a problem yet with this patch applied. Testing without this patch yesterday I saw 3 or 4 lockdep splats in about the same amount of time. I'll leave it going over the weekend just to make sure, though. Robin. > > The patch is straightforward and using non _irq() locking in a workitem > that expects the lock to protect against interrupt handlers on the same > CPU is clearly wrong. > > > Cheers > ---Dave > > > drivers/tty/serial/amba-pl011.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c > index 763eb20..0cc622a 100644 > --- a/drivers/tty/serial/amba-pl011.c > +++ b/drivers/tty/serial/amba-pl011.c > @@ -1360,9 +1360,9 @@ static void pl011_tx_softirq(struct work_struct *work) > struct uart_amba_port *uap = > container_of(dwork, struct uart_amba_port, tx_softirq_work); > > - spin_lock(&uap->port.lock); > + spin_lock_irq(&uap->port.lock); > while (pl011_tx_chars(uap)) ; > - spin_unlock(&uap->port.lock); > + spin_unlock_irq(&uap->port.lock); > } > > static void pl011_tx_irq_seen(struct uart_amba_port *uap) > From mboxrd@z Thu Jan 1 00:00:00 1970 From: robin.murphy@arm.com (Robin Murphy) Date: Fri, 05 Jun 2015 19:03:42 +0100 Subject: [PATCH] serial/amba-pl011: Disable interrupts around TX softirq In-Reply-To: <1433513267-24163-1-git-send-email-Dave.Martin@arm.com> References: <1433513267-24163-1-git-send-email-Dave.Martin@arm.com> Message-ID: <5571E47E.5020800@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 05/06/15 15:07, Dave P Martin wrote: > pl011_tx_softirq() currently uses spin_{,un}lock(), which are not > sufficient to inhibit pl011_int() from being triggered by a local > IRQ and trying to re-take the same lock. This can lead to > deadlocks. > > This patch uses the _irq() locking variants instead to ensure that > pl011_int() handling for a given port is deferred until any > pl011_tx_softirq() work for that port is complete. > > Signed-off-by: Dave Martin > --- > > Another candidate for v4.1 if possible (sorry!) -- I thought this change > was already in, but it went astray when I was refactoring. > > This patch conflicts with tty-next like the previous patch, since it > fixes code that is removed by tty-next. The correct resolution for > the resulting merge conflict is to keep the code from tty-next. > > > I am not 100% certain yet whether some rare deadlocks that Robin is > seeing are caused by this issue, or whether this patch fixes them -- > he's testing atm. FWIW, I've been running Juno in a startup/shutdown loop with a very noisy systemd all afternoon and haven't hit a problem yet with this patch applied. Testing without this patch yesterday I saw 3 or 4 lockdep splats in about the same amount of time. I'll leave it going over the weekend just to make sure, though. Robin. > > The patch is straightforward and using non _irq() locking in a workitem > that expects the lock to protect against interrupt handlers on the same > CPU is clearly wrong. > > > Cheers > ---Dave > > > drivers/tty/serial/amba-pl011.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c > index 763eb20..0cc622a 100644 > --- a/drivers/tty/serial/amba-pl011.c > +++ b/drivers/tty/serial/amba-pl011.c > @@ -1360,9 +1360,9 @@ static void pl011_tx_softirq(struct work_struct *work) > struct uart_amba_port *uap = > container_of(dwork, struct uart_amba_port, tx_softirq_work); > > - spin_lock(&uap->port.lock); > + spin_lock_irq(&uap->port.lock); > while (pl011_tx_chars(uap)) ; > - spin_unlock(&uap->port.lock); > + spin_unlock_irq(&uap->port.lock); > } > > static void pl011_tx_irq_seen(struct uart_amba_port *uap) >