linux-kernel - Re: [PATCH v14 1/2] leds: core: Introduce LED pattern trigger

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Date:   Fri, 9 Nov 2018 09:13:58 +0100
From:   Pavel Machek <pavel@....cz>
To:     Baolin Wang <baolin.wang@...aro.org>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        rteysseyre@...il.com,
        Björn Andersson <bjorn.andersson@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        Linux LED Subsystem <linux-leds@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v14 1/2] leds: core: Introduce LED pattern trigger

On Wed 2018-11-07 11:23:52, Baolin Wang wrote:
> Hi Geert,
> 
> On 6 November 2018 at 23:57, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > Hi Baolin,
> >
> > On Tue, Oct 2, 2018 at 6:39 PM Baolin Wang <baolin.wang@...aro.org> wrote:
> >> This patch adds one new led trigger that LED device can configure
> >> the software or hardware pattern and trigger it.
> >>
> >> Consumers can write 'pattern' file to enable the software pattern
> >> which alters the brightness for the specified duration with one
> >> software timer.
> >>
> >> Moreover consumers can write 'hw_pattern' file to enable the hardware
> >> pattern for some LED controllers which can autonomously control
> >> brightness over time, according to some preprogrammed hardware
> >> patterns.
> >>
> >> Signed-off-by: Raphael Teysseyre <rteysseyre@...il.com>
> >> Signed-off-by: Baolin Wang <baolin.wang@...aro.org>
> >
> >> --- /dev/null
> >> +++ b/drivers/leds/trigger/ledtrig-pattern.c
> >> @@ -0,0 +1,431 @@
> >
> >> +static void pattern_trig_timer_function(struct timer_list *t)
> >> +{
> >> +       struct pattern_trig_data *data = from_timer(data, t, timer);
> >> +
> >> +       mutex_lock(&data->lock);
> >
> > Timer functions run in interrupt context, hence if CONFIG_DEBUG_ATOMIC_SLEEP=y:
> >
> > BUG: sleeping function called from invalid context at kernel/locking/mutex.c:254
> > in_atomic(): 1, irqs_disabled(): 0, pid: 0, name: swapper/1
> > CPU: 1 PID: 0 Comm: swapper/1 Not tainted
> > 4.20.0-rc1-koelsch-00841-ga338c8181013c1a9 #171
> > Hardware name: Generic R-Car Gen2 (Flattened Device Tree)
> > [<c020f19c>] (unwind_backtrace) from [<c020aecc>] (show_stack+0x10/0x14)
> > [<c020aecc>] (show_stack) from [<c07affb8>] (dump_stack+0x7c/0x9c)
> > [<c07affb8>] (dump_stack) from [<c02417d4>] (___might_sleep+0xf4/0x158)
> > [<c02417d4>] (___might_sleep) from [<c07c92c4>] (mutex_lock+0x18/0x60)
> > [<c07c92c4>] (mutex_lock) from [<c067b28c>]
> > (pattern_trig_timer_function+0x1c/0x11c)
> > [<c067b28c>] (pattern_trig_timer_function) from [<c027f6fc>]
> > (call_timer_fn+0x1c/0x90)
> > [<c027f6fc>] (call_timer_fn) from [<c027f944>] (expire_timers+0x94/0xa4)
> > [<c027f944>] (expire_timers) from [<c027fc98>] (run_timer_softirq+0x108/0x15c)
> > [<c027fc98>] (run_timer_softirq) from [<c02021cc>] (__do_softirq+0x1d4/0x258)
> > [<c02021cc>] (__do_softirq) from [<c0224d24>] (irq_exit+0x64/0xc4)
> > [<c0224d24>] (irq_exit) from [<c0268dd0>] (__handle_domain_irq+0x80/0xb4)
> > [<c0268dd0>] (__handle_domain_irq) from [<c045e1b0>] (gic_handle_irq+0x58/0x90)
> > [<c045e1b0>] (gic_handle_irq) from [<c02019f8>] (__irq_svc+0x58/0x74)
> > Exception stack(0xeb483f60 to 0xeb483fa8)
> > 3f60: 00000000 00000000 eb9afaa0 c0217e80 00000000 ffffe000 00000000 c0e06408
> > 3f80: 00000002 c0e0647c c0c6a5f0 00000000 c0e04900 eb483fb0 c0207ea8 c0207e98
> > 3fa0: 60020013 ffffffff
> > [<c02019f8>] (__irq_svc) from [<c0207e98>] (arch_cpu_idle+0x1c/0x38)
> > [<c0207e98>] (arch_cpu_idle) from [<c0247ca8>] (do_idle+0x138/0x268)
> > [<c0247ca8>] (do_idle) from [<c0248050>] (cpu_startup_entry+0x18/0x1c)
> > [<c0248050>] (cpu_startup_entry) from [<402022ec>] (0x402022ec)
> >
> > Either this should use a spinlock instead of a mutex, or the timer
> > function should kick a workqueue to do the real work.
> >
> 
> Ah, sorry I missed this. Good catch.
> 
> After more thinking, the easy fix is that I think we can remove the
> mutex lock in pattern_trig_timer_function(). Since the mutex lock is
> used to protect the pattern trigger data, but before changing new
> pattern trigger data (pattern values or repeat value) by users, we
> always cancel the timer firstly to clear previous patterns'
> performance. That means there is no race in
> pattern_trig_timer_function(), so we can drop the mutex lock in
> pattern_trig_timer_function() to avoid this issue.
> 
> I will send one patch to fix this issue. Thanks.

That's kind of interesting, but yes, it should work.

									Pavel

-- 
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