Re: [PATCH] irqchip/meson-gpio: Fix HARDIRQ-safe -> HARDIRQ-unsafe lock order

Marc Zyngier
2020-04-16T09:41:02Z

On Tue, 14 Apr 2020 17:52:25 +0200
Jerome Brunet <jbrunet@baylibre.com> wrote:

Hi Jerome,

> On Tue 14 Apr 2020 at 15:20, Marc Zyngier <maz@kernel.org> wrote:
>
> > On Tue, 7 Apr 2020 15:46:58 +0100
> > Marc Zyngier <maz@kernel.org> wrote:
> >
> > +Jerome, Martin,
> >
> >> Running a lockedp-enabled kernel on a vim3l board (Amlogic SM1)
> >> leads to the following splat:
> >>
> >> [ 13.557138] WARNING: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected
> >> [ 13.587485] ip/456 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
> >> [ 13.625922] ffff000059908cf0 (&irq_desc_lock_class){-.-.}-{2:2}, at: __setup_irq+0xf8/0x8d8
> >> [ 13.632273] which would create a new lock dependency:
> >> [ 13.637272] (&irq_desc_lock_class){-.-.}-{2:2} -> (&ctl->lock){+.+.}-{2:2}
> >> [ 13.644209]
> >> [ 13.644209] but this new dependency connects a HARDIRQ-irq-safe lock:
> >> [ 13.654122] (&irq_desc_lock_class){-.-.}-{2:2}
> >> [ 13.654125]
> >> [ 13.654125] ... which became HARDIRQ-irq-safe at:
> >> [ 13.664759] lock_acquire+0xec/0x368
> >> [ 13.666926] _raw_spin_lock+0x60/0x88
> >> [ 13.669979] handle_fasteoi_irq+0x30/0x178
> >> [ 13.674082] generic_handle_irq+0x38/0x50
> >> [ 13.678098] __handle_domain_irq+0x6c/0xc8
> >> [ 13.682209] gic_handle_irq+0x5c/0xb0
> >> [ 13.685872] el1_irq+0xd0/0x180
> >> [ 13.689010] arch_cpu_idle+0x40/0x220
> >> [ 13.692732] default_idle_call+0x54/0x60
> >> [ 13.696677] do_idle+0x23c/0x2e8
> >> [ 13.699903] cpu_startup_entry+0x30/0x50
> >> [ 13.703852] rest_init+0x1e0/0x2b4
> >> [ 13.707301] arch_call_rest_init+0x18/0x24
> >> [ 13.711449] start_kernel+0x4ec/0x51c
> >> [ 13.715167]
> >> [ 13.715167] to a HARDIRQ-irq-unsafe lock:
> >> [ 13.722426] (&ctl->lock){+.+.}-{2:2}
> >> [ 13.722430]
> >> [ 13.722430] ... which became HARDIRQ-irq-unsafe at:
> >> [ 13.732319] ...
> >> [ 13.732324] lock_acquire+0xec/0x368
> >> [ 13.735985] _raw_spin_lock+0x60/0x88
> >> [ 13.739452] meson_gpio_irq_domain_alloc+0xcc/0x290
> >> [ 13.744392] irq_domain_alloc_irqs_hierarchy+0x24/0x60
> >> [ 13.749586] __irq_domain_alloc_irqs+0x160/0x2f0
> >> [ 13.754254] irq_create_fwspec_mapping+0x118/0x320
> >> [ 13.759073] irq_create_of_mapping+0x78/0xa0
> >> [ 13.763360] of_irq_get+0x6c/0x80
> >> [ 13.766701] of_mdiobus_register_phy+0x10c/0x238 [of_mdio]
> >> [ 13.772227] of_mdiobus_register+0x158/0x380 [of_mdio]
> >> [ 13.777388] mdio_mux_init+0x180/0x2e8 [mdio_mux]
> >> [ 13.782128] g12a_mdio_mux_probe+0x290/0x398 [mdio_mux_meson_g12a]
> >> [ 13.788349] platform_drv_probe+0x5c/0xb0
> >> [ 13.792379] really_probe+0xe4/0x448
> >> [ 13.795979] driver_probe_device+0xe8/0x140
> >> [ 13.800189] __device_attach_driver+0x94/0x120
> >> [ 13.804639] bus_for_each_drv+0x84/0xd8
> >> [ 13.808474] __device_attach+0xe4/0x168
> >> [ 13.812361] device_initial_probe+0x1c/0x28
> >> [ 13.816592] bus_probe_device+0xa4/0xb0
> >> [ 13.820430] deferred_probe_work_func+0xa8/0x100
> >> [ 13.825064] process_one_work+0x264/0x688
> >> [ 13.829088] worker_thread+0x4c/0x458
> >> [ 13.832768] kthread+0x154/0x158
> >> [ 13.836018] ret_from_fork+0x10/0x18
> >> [ 13.839612]
> >> [ 13.839612] other info that might help us debug this:
> >> [ 13.839612]
> >> [ 13.850354] Possible interrupt unsafe locking scenario:
> >> [ 13.850354]
> >> [ 13.855720] CPU0 CPU1
> >> [ 13.858774] ---- ----
> >> [ 13.863242] lock(&ctl->lock);
> >> [ 13.866330] local_irq_disable();
> >> [ 13.872233] lock(&irq_desc_lock_class);
> >> [ 13.878705] lock(&ctl->lock);
> >> [ 13.884297] <Interrupt>
> >> [ 13.886857] lock(&irq_desc_lock_class);
> >> [ 13.891014]
> >> [ 13.891014] *** DEADLOCK ***
> >>
> >> The issue can occur when CPU1 is doing something like irq_set_type()
> >> and CPU0 performing an interrupt allocation, for example. Taking
> >> an interrupt (like the one being reconfigured) would lead to a
> >> deadlock.
>
> Just to make sure I understand
> * the 1st trace is a CPU getting interrupted while setting the irq type
> * the 2nd trace is another CPU trying to allocate an irq for network PHY.

The traces are only what lockdep sees as a dangerous behaviour, not
necessarily what actually leads to a deadlock. The deadlock scenario is
the one outlined just before "*** DEADLOCK ***", and a way to get there
is my interpretation just above.

> >>
> >> A solution to this is:
> >>
> >> - Reorder the locking so that meson_gpio_irq_update_bits takes the lock
> >> itself at all times, instead of relying on the caller to lock or not,
> >> hence making the RMW sequence atomic,
> >>
> >> - Rework the critical section in meson_gpio_irq_request_channel to only
> >> cover the allocation itself, and let the gpio_irq_sel_pin callback
> >> deal with its own locking if required,
> >>
> >> - Take the private spin-lock with interrupts disabled at all times
>
> Looks like the only safe path if I understand correctly.
> The patch below looks good to me.
>
> >>
> >> Signed-off-by: Marc Zyngier <maz@kernel.org>
>
> Thanks for the fix Marc.
>
> Reviewed-by: Jerome Brunet <jbrunet@baylibre.com>

Thanks,

M.
--
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