From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave.Martin@arm.com (Dave P Martin) Date: Mon, 8 Jun 2015 12:34:11 +0100 Subject: [PATCH] serial/amba-pl011: Disable interrupts around TX softirq In-Reply-To: <55756FC5.5000801@arm.com> References: <1433513267-24163-1-git-send-email-Dave.Martin@arm.com> <5571E47E.5020800@arm.com> <55756FC5.5000801@arm.com> Message-ID: <20150608113406.GA3654@e103592.cambridge.arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, Jun 08, 2015 at 11:34:45AM +0100, Robin Murphy wrote: > On 05/06/15 19:03, Robin Murphy wrote: > > 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. > > Having still seen nothing over several hundred more reboot cycles, I'm > satisfied that the irq vs. softirq race explains the deadlock and that > this patch fixes it, so; > > Tested-by: Robin Murphy Thanks for this Cheers ---Dave From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave P Martin Subject: Re: [PATCH] serial/amba-pl011: Disable interrupts around TX softirq Date: Mon, 8 Jun 2015 12:34:11 +0100 Message-ID: <20150608113406.GA3654@e103592.cambridge.arm.com> References: <1433513267-24163-1-git-send-email-Dave.Martin@arm.com> <5571E47E.5020800@arm.com> <55756FC5.5000801@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <55756FC5.5000801@arm.com> Content-Disposition: inline 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: Robin Murphy Cc: Russell King , Jakub =?utf-8?B?S2ljacWEc2tp?= , Greg Kroah-Hartman , Andrew Jackson , Graeme Gregory , "linux-serial@vger.kernel.org" , Andre Przywara , popcorn mix , Jorge Ramirez-Ortiz , "linux-arm-kernel@lists.infradead.org" List-Id: linux-serial@vger.kernel.org On Mon, Jun 08, 2015 at 11:34:45AM +0100, Robin Murphy wrote: > On 05/06/15 19:03, Robin Murphy wrote: > > 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. > > Having still seen nothing over several hundred more reboot cycles, I'm > satisfied that the irq vs. softirq race explains the deadlock and that > this patch fixes it, so; > > Tested-by: Robin Murphy Thanks for this Cheers ---Dave