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Date:   Wed, 25 Nov 2020 22:01:26 +0800
From:   Boqun Feng <boqun.feng@gmail.com>
To:     Pavel Machek <pavel@ucw.cz>
Cc:     Andrea Righi <andrea.righi@canonical.com>,
        Dan Murphy <dmurphy@ti.com>, linux-leds@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] leds: trigger: fix potential deadlock with libata
Message-ID: <20201125140126.GH3025@boqun-archlinux>
References: <20201102104152.GG9930@xps-13-7390>
 <20201125124648.GJ29328@amd>
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In-Reply-To: <20201125124648.GJ29328@amd>
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On Wed, Nov 25, 2020 at 01:46:48PM +0100, Pavel Machek wrote:
> Hi!
> 
> > We have the following potential deadlock condition:
> > 
> >  ========================================================
> >  WARNING: possible irq lock inversion dependency detected
> >  5.10.0-rc2+ #25 Not tainted
> >  --------------------------------------------------------
> >  swapper/3/0 just changed the state of lock:
> >  ffff8880063bd618 (&host->lock){-...}-{2:2}, at: ata_bmdma_interrupt+0x27/0x200
> >  but this lock took another, HARDIRQ-READ-unsafe lock in the past:
> >   (&trig->leddev_list_lock){.+.?}-{2:2}
> > 
> >  and interrupts could create inverse lock ordering between them.
> > 
> >  other info that might help us debug this:
> >   Possible interrupt unsafe locking scenario:
> > 
> >         CPU0                    CPU1
> >         ----                    ----
> >    lock(&trig->leddev_list_lock);
> >                                 local_irq_disable();
> >                                 lock(&host->lock);
> >                                 lock(&trig->leddev_list_lock);
> >    <Interrupt>
> >      lock(&host->lock);
> > 
> >   *** DEADLOCK ***
> > 
> >  no locks held by swapper/3/0.
> > 
> >  the shortest dependencies between 2nd lock and 1st lock:
> >   -> (&trig->leddev_list_lock){.+.?}-{2:2} ops: 46 {
> >      HARDIRQ-ON-R at:
> >                        lock_acquire+0x15f/0x420
> >                        _raw_read_lock+0x42/0x90
> >                        led_trigger_event+0x2b/0x70
> >                        rfkill_global_led_trigger_worker+0x94/0xb0
> >                        process_one_work+0x240/0x560
> >                        worker_thread+0x58/0x3d0
> >                        kthread+0x151/0x170
> >                        ret_from_fork+0x1f/0x30
> >      IN-SOFTIRQ-R at:
> >                        lock_acquire+0x15f/0x420
> >                        _raw_read_lock+0x42/0x90
> >                        led_trigger_event+0x2b/0x70
> >                        kbd_bh+0x9e/0xc0
> >                        tasklet_action_common.constprop.0+0xe9/0x100
> >                        tasklet_action+0x22/0x30
> >                        __do_softirq+0xcc/0x46d
> >                        run_ksoftirqd+0x3f/0x70
> >                        smpboot_thread_fn+0x116/0x1f0
> >                        kthread+0x151/0x170
> >                        ret_from_fork+0x1f/0x30
> >      SOFTIRQ-ON-R at:
> >                        lock_acquire+0x15f/0x420
> >                        _raw_read_lock+0x42/0x90
> >                        led_trigger_event+0x2b/0x70
> >                        rfkill_global_led_trigger_worker+0x94/0xb0
> >                        process_one_work+0x240/0x560
> >                        worker_thread+0x58/0x3d0
> >                        kthread+0x151/0x170
> >                        ret_from_fork+0x1f/0x30
> >      INITIAL READ USE at:
> >                            lock_acquire+0x15f/0x420
> >                            _raw_read_lock+0x42/0x90
> >                            led_trigger_event+0x2b/0x70
> >                            rfkill_global_led_trigger_worker+0x94/0xb0
> >                            process_one_work+0x240/0x560
> >                            worker_thread+0x58/0x3d0
> >                            kthread+0x151/0x170
> >                            ret_from_fork+0x1f/0x30
> >    }
> >    ... key      at: [<ffffffff83da4c00>] __key.0+0x0/0x10
> >    ... acquired at:
> >     _raw_read_lock+0x42/0x90
> >     led_trigger_blink_oneshot+0x3b/0x90
> >     ledtrig_disk_activity+0x3c/0xa0
> >     ata_qc_complete+0x26/0x450
> >     ata_do_link_abort+0xa3/0xe0
> >     ata_port_freeze+0x2e/0x40
> >     ata_hsm_qc_complete+0x94/0xa0
> >     ata_sff_hsm_move+0x177/0x7a0
> >     ata_sff_pio_task+0xc7/0x1b0
> >     process_one_work+0x240/0x560
> >     worker_thread+0x58/0x3d0
> >     kthread+0x151/0x170
> >     ret_from_fork+0x1f/0x30
> > 
> >  -> (&host->lock){-...}-{2:2} ops: 69 {
> >     IN-HARDIRQ-W at:
> >                      lock_acquire+0x15f/0x420
> >                      _raw_spin_lock_irqsave+0x52/0xa0
> >                      ata_bmdma_interrupt+0x27/0x200
> >                      __handle_irq_event_percpu+0xd5/0x2b0
> >                      handle_irq_event+0x57/0xb0
> >                      handle_edge_irq+0x8c/0x230
> >                      asm_call_irq_on_stack+0xf/0x20
> >                      common_interrupt+0x100/0x1c0
> >                      asm_common_interrupt+0x1e/0x40
> >                      native_safe_halt+0xe/0x10
> >                      arch_cpu_idle+0x15/0x20
> >                      default_idle_call+0x59/0x1c0
> >                      do_idle+0x22c/0x2c0
> >                      cpu_startup_entry+0x20/0x30
> >                      start_secondary+0x11d/0x150
> >                      secondary_startup_64_no_verify+0xa6/0xab
> >     INITIAL USE at:
> >                     lock_acquire+0x15f/0x420
> >                     _raw_spin_lock_irqsave+0x52/0xa0
> >                     ata_dev_init+0x54/0xe0
> >                     ata_link_init+0x8b/0xd0
> >                     ata_port_alloc+0x1f1/0x210
> >                     ata_host_alloc+0xf1/0x130
> >                     ata_host_alloc_pinfo+0x14/0xb0
> >                     ata_pci_sff_prepare_host+0x41/0xa0
> >                     ata_pci_bmdma_prepare_host+0x14/0x30
> >                     piix_init_one+0x21f/0x600
> >                     local_pci_probe+0x48/0x80
> >                     pci_device_probe+0x105/0x1c0
> >                     really_probe+0x221/0x490
> >                     driver_probe_device+0xe9/0x160
> >                     device_driver_attach+0xb2/0xc0
> >                     __driver_attach+0x91/0x150
> >                     bus_for_each_dev+0x81/0xc0
> >                     driver_attach+0x1e/0x20
> >                     bus_add_driver+0x138/0x1f0
> >                     driver_register+0x91/0xf0
> >                     __pci_register_driver+0x73/0x80
> >                     piix_init+0x1e/0x2e
> >                     do_one_initcall+0x5f/0x2d0
> >                     kernel_init_freeable+0x26f/0x2cf
> >                     kernel_init+0xe/0x113
> >                     ret_from_fork+0x1f/0x30
> >   }
> >   ... key      at: [<ffffffff83d9fdc0>] __key.6+0x0/0x10
> >   ... acquired at:
> >     __lock_acquire+0x9da/0x2370
> >     lock_acquire+0x15f/0x420
> >     _raw_spin_lock_irqsave+0x52/0xa0
> >     ata_bmdma_interrupt+0x27/0x200
> >     __handle_irq_event_percpu+0xd5/0x2b0
> >     handle_irq_event+0x57/0xb0
> >     handle_edge_irq+0x8c/0x230
> >     asm_call_irq_on_stack+0xf/0x20
> >     common_interrupt+0x100/0x1c0
> >     asm_common_interrupt+0x1e/0x40
> >     native_safe_halt+0xe/0x10
> >     arch_cpu_idle+0x15/0x20
> >     default_idle_call+0x59/0x1c0
> >     do_idle+0x22c/0x2c0
> >     cpu_startup_entry+0x20/0x30
> >     start_secondary+0x11d/0x150
> >     secondary_startup_64_no_verify+0xa6/0xab
> > 
> > This lockdep splat is reported after:
> > commit e918188611f0 ("locking: More accurate annotations for read_lock()")
> > 
> > To clarify:
> >  - read-locks are recursive only in interrupt context (when
> >    in_interrupt() returns true)
> >  - after acquiring host->lock in CPU1, another cpu (i.e. CPU2) may call
> >    write_lock(&trig->leddev_list_lock) that would be blocked by CPU0
> >    that holds trig->leddev_list_lock in read-mode
> >  - when CPU1 (ata_ac_complete()) tries to read-lock
> >    trig->leddev_list_lock, it would be blocked by the write-lock waiter
> >    on CPU2 (because we are not in interrupt context, so the read-lock is
> >    not recursive)
> >  - at this point if an interrupt happens on CPU0 and
> >    ata_bmdma_interrupt() is executed it will try to acquire host->lock,
> >    that is held by CPU1, that is currently blocked by CPU2, so:
> > 
> >    * CPU0 blocked by CPU1
> >    * CPU1 blocked by CPU2
> >    * CPU2 blocked by CPU0
> > 
> >      *** DEADLOCK ***
> > 
> > The deadlock scenario is better represented by the following schema
> > (thanks to Boqun Feng <boqun.feng@gmail.com> for the schema and the
> > detailed explanation of the deadlock condition):
> > 
> >  CPU 0:                          CPU 1:                        CPU 2:
> >  -----                           -----                         -----
> >  led_trigger_event():
> >    read_lock(&trig->leddev_list_lock);
> >  				<workqueue>
> >  				ata_hsm_qc_complete():
> >  				  spin_lock_irqsave(&host->lock);
> >  								write_lock(&trig->leddev_list_lock);
> >  				  ata_port_freeze():
> >  				    ata_do_link_abort():
> >  				      ata_qc_complete():
> >  					ledtrig_disk_activity():
> >  					  led_trigger_blink_oneshot():
> >  					    read_lock(&trig->leddev_list_lock);
> >  					    // ^ not in in_interrupt() context, so could get blocked by CPU 2
> >  <interrupt>
> >    ata_bmdma_interrupt():
> >      spin_lock_irqsave(&host->lock);
> > 
> > Fix by using read_lock_irqsave/irqrestore() in led_trigger_event(), so
> > that no interrupt can happen in between, preventing the deadlock
> > condition.
> > 
> > Link: https://lore.kernel.org/lkml/20201101092614.GB3989@xps-13-7390/
> > Fixes: eb25cb9956cc ("leds: convert IDE trigger to common disk trigger")
> > Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
> 
> I'd hate to see this in stable 3 days after Linus merges it...
> 
> Do these need _irqsave, too?
> 
> drivers/leds/led-triggers.c:   read_lock(&trig->leddev_list_lock);
> drivers/leds/led-triggers.c:   read_unlock(&trig->leddev_list_lock);
> drivers/leds/led-triggers.c:   read_lock(&trig->leddev_list_lock);
> drivers/leds/led-triggers.c:   read_unlock(&trig->leddev_list_lock);
> 

I think so, if you mean the read_{un,}lock in led_trigger_blink_setup()
also need to convert to irq-safe version ;-)

Regards,
Boqun

> Best regards,
> 								Pavel
> 
> > ---
> >  drivers/leds/led-triggers.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
> > index 91da90cfb11d..16d1a93a10a8 100644
> > --- a/drivers/leds/led-triggers.c
> > +++ b/drivers/leds/led-triggers.c
> > @@ -378,14 +378,15 @@ void led_trigger_event(struct led_trigger *trig,
> >  			enum led_brightness brightness)
> >  {
> >  	struct led_classdev *led_cdev;
> > +	unsigned long flags;
> >  
> >  	if (!trig)
> >  		return;
> >  
> > -	read_lock(&trig->leddev_list_lock);
> > +	read_lock_irqsave(&trig->leddev_list_lock, flags);
> >  	list_for_each_entry(led_cdev, &trig->led_cdevs, trig_list)
> >  		led_set_brightness(led_cdev, brightness);
> > -	read_unlock(&trig->leddev_list_lock);
> > +	read_unlock_irqrestore(&trig->leddev_list_lock, flags);
> >  }
> >  EXPORT_SYMBOL_GPL(led_trigger_event);
> >  
> 
> -- 
> http://www.livejournal.com/~pavelmachek