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Received: from shell.armlinux.org.uk ([2001:4d48:ad52:3201:5054:ff:fe00:4ec]:54548) by pandora.armlinux.org.uk with esmtpsa (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.90_1) (envelope-from ) id 1gvSX7-0002IG-G7; Sun, 17 Feb 2019 19:55:25 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.89) (envelope-from ) id 1gvSX6-0006Xk-RG; Sun, 17 Feb 2019 19:55:24 +0000 Date: Sun, 17 Feb 2019 19:55:24 +0000 From: Russell King - ARM Linux admin To: Andrew Lunn Cc: netdev , Vivien Didelot Subject: Re: [PATCH] net: dsa: mv88e6xxx: Add lockdep classes to fix false positive splat Message-ID: <20190217195524.rhc4rsvzsalptyua@shell.armlinux.org.uk> References: <20190217181143.14817-1-andrew@lunn.ch> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190217181143.14817-1-andrew@lunn.ch> User-Agent: NeoMutt/20170113 (1.7.2) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Sun, Feb 17, 2019 at 07:11:43PM +0100, Andrew Lunn wrote: > The following false positive lockdep splat has been observed. > > ====================================================== > WARNING: possible circular locking dependency detected > 4.20.0+ #302 Not tainted > ------------------------------------------------------ > systemd-udevd/160 is trying to acquire lock: > edea6080 (&chip->reg_lock){+.+.}, at: __setup_irq+0x640/0x704 > > but task is already holding lock: > edff0340 (&desc->request_mutex){+.+.}, at: __setup_irq+0xa0/0x704 > > which lock already depends on the new lock. > > the existing dependency chain (in reverse order) is: > > -> #1 (&desc->request_mutex){+.+.}: > mutex_lock_nested+0x1c/0x24 > __setup_irq+0xa0/0x704 > request_threaded_irq+0xd0/0x150 > mv88e6xxx_probe+0x41c/0x694 [mv88e6xxx] > mdio_probe+0x2c/0x54 > really_probe+0x200/0x2c4 > driver_probe_device+0x5c/0x174 > __driver_attach+0xd8/0xdc > bus_for_each_dev+0x58/0x7c > bus_add_driver+0xe4/0x1f0 > driver_register+0x7c/0x110 > mdio_driver_register+0x24/0x58 > do_one_initcall+0x74/0x2e8 > do_init_module+0x60/0x1d0 > load_module+0x1968/0x1ff4 > sys_finit_module+0x8c/0x98 > ret_fast_syscall+0x0/0x28 > 0xbedf2ae8 > > -> #0 (&chip->reg_lock){+.+.}: > __mutex_lock+0x50/0x8b8 > mutex_lock_nested+0x1c/0x24 > __setup_irq+0x640/0x704 > request_threaded_irq+0xd0/0x150 > mv88e6xxx_g2_irq_setup+0xcc/0x1b4 [mv88e6xxx] > mv88e6xxx_probe+0x44c/0x694 [mv88e6xxx] > mdio_probe+0x2c/0x54 > really_probe+0x200/0x2c4 > driver_probe_device+0x5c/0x174 > __driver_attach+0xd8/0xdc > bus_for_each_dev+0x58/0x7c > bus_add_driver+0xe4/0x1f0 > driver_register+0x7c/0x110 > mdio_driver_register+0x24/0x58 > do_one_initcall+0x74/0x2e8 > do_init_module+0x60/0x1d0 > load_module+0x1968/0x1ff4 > sys_finit_module+0x8c/0x98 > ret_fast_syscall+0x0/0x28 > 0xbedf2ae8 > > other info that might help us debug this: > > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > lock(&desc->request_mutex); > lock(&chip->reg_lock); > lock(&desc->request_mutex); > lock(&chip->reg_lock); > > &desc->request_mutex refer to two different mutex. #1 is the GPIO for > the chip interrupt. #2 is the chained interrupt between global 1 and > global 2. > > Add lockdep classes to the GPIO interrupt to avoid this. > > Reported-by: Russell King > Signed-off-by: Andrew Lunn > --- > > Hi Russell > > Does this fix it for you on Clearfog? Yes, that also fixes the problem, but I do think this is just papering over mv88e6xxx needlessly holding locks when it doesn't need to do so. > > drivers/net/dsa/mv88e6xxx/chip.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c > index 32e7af5caa69..936d53a92144 100644 > --- a/drivers/net/dsa/mv88e6xxx/chip.c > +++ b/drivers/net/dsa/mv88e6xxx/chip.c > @@ -442,12 +442,20 @@ static int mv88e6xxx_g1_irq_setup_common(struct mv88e6xxx_chip *chip) > > static int mv88e6xxx_g1_irq_setup(struct mv88e6xxx_chip *chip) > { > + static struct lock_class_key lock_key; > + static struct lock_class_key request_key; > int err; > > err = mv88e6xxx_g1_irq_setup_common(chip); > if (err) > return err; > > + /* These lock classes tells lockdep that global 1 irqs are in > + * a different category than their parent GPIO, so it won't > + * report false recursion. > + */ > + irq_set_lockdep_class(chip->irq, &lock_key, &request_key); > + > err = request_threaded_irq(chip->irq, NULL, > mv88e6xxx_g1_irq_thread_fn, > IRQF_ONESHOT | IRQF_SHARED, > -- > 2.20.1 > > -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up