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Message-ID: <20220720034300.6d2905b8@wim.jer> Date: Wed, 20 Jul 2022 03:43:00 +0200 From: Jeroen Roovers <jer@...all.nl> To: "Guilherme G. Piccoli" <gpiccoli@...lia.com> Cc: akpm@...ux-foundation.org, bhe@...hat.com, pmladek@...e.com, kexec@...ts.infradead.org, linux-kernel@...r.kernel.org, linux-hyperv@...r.kernel.org, netdev@...r.kernel.org, x86@...nel.org, kernel-dev@...lia.com, kernel@...ccoli.net, halves@...onical.com, fabiomirmar@...il.com, alejandro.j.jimenez@...cle.com, andriy.shevchenko@...ux.intel.com, arnd@...db.de, bp@...en8.de, corbet@....net, d.hatayama@...fujitsu.com, dave.hansen@...ux.intel.com, dyoung@...hat.com, feng.tang@...el.com, gregkh@...uxfoundation.org, mikelley@...rosoft.com, hidehiro.kawai.ez@...achi.com, jgross@...e.com, john.ogness@...utronix.de, keescook@...omium.org, luto@...nel.org, mhiramat@...nel.org, mingo@...hat.com, paulmck@...nel.org, peterz@...radead.org, rostedt@...dmis.org, senozhatsky@...omium.org, stern@...land.harvard.edu, tglx@...utronix.de, vgoyal@...hat.com, vkuznets@...hat.com, will@...nel.org, linux-parisc@...r.kernel.org, "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>, Helge Deller <deller@....de> Subject: Re: [PATCH v2 07/13] parisc: Replace regular spinlock with spin_trylock on panic path Hi Guilherme, On Tue, 19 Jul 2022 16:53:20 -0300 "Guilherme G. Piccoli" <gpiccoli@...lia.com> wrote: > The panic notifiers' callbacks execute in an atomic context, with > interrupts/preemption disabled, and all CPUs not running the panic > function are off, so it's very dangerous to wait on a regular > spinlock, there's a risk of deadlock. > > Refactor the panic notifier of parisc/power driver to make use > of spin_trylock - for that, we've added a second version of the > soft-power function. Also, some comments were reorganized and > trailing white spaces, useless header inclusion and blank lines > were removed. > > Cc: "James E.J. Bottomley" <James.Bottomley@...senPartnership.com> > Acked-by: Helge Deller <deller@....de> # parisc > Signed-off-by: Guilherme G. Piccoli <gpiccoli@...lia.com> > > --- > > V2: > - Added Helge's ACK - thanks! > > arch/parisc/include/asm/pdc.h | 1 + > arch/parisc/kernel/firmware.c | 27 +++++++++++++++++++++++---- > drivers/parisc/power.c | 17 ++++++++++------- > 3 files changed, 34 insertions(+), 11 deletions(-) > > diff --git a/arch/parisc/include/asm/pdc.h > b/arch/parisc/include/asm/pdc.h index b643092d4b98..7a106008e258 > 100644 --- a/arch/parisc/include/asm/pdc.h > +++ b/arch/parisc/include/asm/pdc.h > @@ -83,6 +83,7 @@ int pdc_do_firm_test_reset(unsigned long > ftc_bitmap); int pdc_do_reset(void); > int pdc_soft_power_info(unsigned long *power_reg); > int pdc_soft_power_button(int sw_control); > +int pdc_soft_power_button_panic(int sw_control); > void pdc_io_reset(void); > void pdc_io_reset_devices(void); > int pdc_iodc_getc(void); > diff --git a/arch/parisc/kernel/firmware.c > b/arch/parisc/kernel/firmware.c index 6a7e315bcc2e..0e2f70b592f4 > 100644 --- a/arch/parisc/kernel/firmware.c > +++ b/arch/parisc/kernel/firmware.c > @@ -1232,15 +1232,18 @@ int __init pdc_soft_power_info(unsigned long > *power_reg) } > > /* > - * pdc_soft_power_button - Control the soft power button behaviour > - * @sw_control: 0 for hardware control, 1 for software control > + * pdc_soft_power_button{_panic} - Control the soft power button > behaviour > + * @sw_control: 0 for hardware control, 1 for software control > * > * > * This PDC function places the soft power button under software or > * hardware control. > - * Under software control the OS may control to when to allow to > shut > - * down the system. Under hardware control pressing the power button > + * Under software control the OS may control to when to allow to shut > + * down the system. Under hardware control pressing the power button > * powers off the system immediately. > + * > + * The _panic version relies in spin_trylock to prevent deadlock > + * on panic path. in => on > */ > int pdc_soft_power_button(int sw_control) > { > @@ -1254,6 +1257,22 @@ int pdc_soft_power_button(int sw_control) > return retval; > } > > +int pdc_soft_power_button_panic(int sw_control) > +{ > + int retval; > + unsigned long flags; > + > + if (!spin_trylock_irqsave(&pdc_lock, flags)) { > + pr_emerg("Couldn't enable soft power button\n"); > + return -EBUSY; /* ignored by the panic notifier */ > + } > + > + retval = mem_pdc_call(PDC_SOFT_POWER, PDC_SOFT_POWER_ENABLE, > __pa(pdc_result), sw_control); > + spin_unlock_irqrestore(&pdc_lock, flags); > + > + return retval; > +} > + > /* > * pdc_io_reset - Hack to avoid overlapping range registers of > Bridges devices. > * Primarily a problem on T600 (which parisc-linux doesn't support) > but diff --git a/drivers/parisc/power.c b/drivers/parisc/power.c > index 456776bd8ee6..8512884de2cf 100644 > --- a/drivers/parisc/power.c > +++ b/drivers/parisc/power.c > @@ -37,7 +37,6 @@ > #include <linux/module.h> > #include <linux/init.h> > #include <linux/kernel.h> > -#include <linux/notifier.h> > #include <linux/panic_notifier.h> > #include <linux/reboot.h> > #include <linux/sched/signal.h> > @@ -175,16 +174,21 @@ static void powerfail_interrupt(int code, void > *x) > > > -/* parisc_panic_event() is called by the panic handler. > - * As soon as a panic occurs, our tasklets above will not be > - * executed any longer. This function then re-enables the > - * soft-power switch and allows the user to switch off the system > +/* > + * parisc_panic_event() is called by the panic handler. > + * > + * As soon as a panic occurs, our tasklets above will not > + * be executed any longer. This function then re-enables > + * the soft-power switch and allows the user to switch off > + * the system. We rely in pdc_soft_power_button_panic() > + * since this version spin_trylocks (instead of regular > + * spinlock), preventing deadlocks on panic path. > */ > static int parisc_panic_event(struct notifier_block *this, > unsigned long event, void *ptr) > { > /* re-enable the soft-power switch */ > - pdc_soft_power_button(0); > + pdc_soft_power_button_panic(0); > return NOTIFY_DONE; > } > > @@ -193,7 +197,6 @@ static struct notifier_block parisc_panic_block = > { .priority = INT_MAX, > }; > > - > static int __init power_init(void) > { > unsigned long ret; Kind regards, jer
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