Re: [PATCH v8 16/27] m68k: Switch to new sys-off handler API

[Dmitry Osipenko <dmitry.osipenko@collabora.com>]

On 5/31/22 22:04, Geert Uytterhoeven wrote:
> Hi Dmitry,
> 
> On Tue, May 10, 2022 at 1:34 AM Dmitry Osipenko
> <dmitry.osipenko@collabora.com> wrote:
>> Kernel now supports chained power-off handlers. Use
>> register_power_off_handler() that registers power-off handlers and
>> do_kernel_power_off() that invokes chained power-off handlers. Legacy
>> pm_power_off() will be removed once all drivers will be converted to
>> the new sys-off API.
>>
>> Normally arch code should adopt only the do_kernel_power_off() at first,
>> but m68k is a special case because it uses pm_power_off() "inside out",
>> i.e. pm_power_off() invokes machine_power_off() [in fact it does nothing],
>> while it's machine_power_off() that should invoke the pm_power_off(), and
>> thus, we can't convert platforms to the new API separately. There are only
>> two platforms changed here, so it's not a big deal.
>>
>> Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
>> Reviewed-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> 
> Thanks for your patch, which is now commit f0f7e5265b3b37b0
> ("m68k: Switch to new sys-off handler API") upstream.
> 
>> --- a/arch/m68k/emu/natfeat.c
>> +++ b/arch/m68k/emu/natfeat.c
>> @@ -15,6 +15,7 @@
>>  #include <linux/string.h>
>>  #include <linux/kernel.h>
>>  #include <linux/module.h>
>> +#include <linux/reboot.h>
>>  #include <linux/io.h>
>>  #include <asm/machdep.h>
>>  #include <asm/natfeat.h>
>> @@ -90,5 +91,5 @@ void __init nf_init(void)
>>         pr_info("NatFeats found (%s, %lu.%lu)\n", buf, version >> 16,
>>                 version & 0xffff);
>>
>> -       mach_power_off = nf_poweroff;
>> +       register_platform_power_off(nf_poweroff);
> 
> Unfortunately nothing is registered, as this is called very early
> (from setup_arch(), before the memory allocator is available.
> Hence register_sys_off_handler() fails with -ENOMEM, and poweroff
> stops working.
> 
> Possible solutions:
>   - As at most one handler can be registered,
>     register_platform_power_off() could use a static struct sys_off_handler
>     instance,
>   - Keep mach_power_off, and call register_platform_power_off() later.
> 
> Anything else?
> Thanks!
> 
>> --- a/arch/m68k/mac/config.c
>> +++ b/arch/m68k/mac/config.c
>> @@ -12,6 +12,7 @@
>>
>>  #include <linux/errno.h>
>>  #include <linux/module.h>
>> +#include <linux/reboot.h>
>>  #include <linux/types.h>
>>  #include <linux/mm.h>
>>  #include <linux/tty.h>
>> @@ -140,7 +141,6 @@ void __init config_mac(void)
>>         mach_hwclk = mac_hwclk;
>>         mach_reset = mac_reset;
>>         mach_halt = mac_poweroff;
>> -       mach_power_off = mac_poweroff;
>>  #if IS_ENABLED(CONFIG_INPUT_M68K_BEEP)
>>         mach_beep = mac_mksound;
>>  #endif
>> @@ -160,6 +160,8 @@ void __init config_mac(void)
>>
>>         if (macintosh_config->ident == MAC_MODEL_IICI)
>>                 mach_l2_flush = via_l2_flush;
>> +
>> +       register_platform_power_off(mac_poweroff);
>>  }
> 
> This must have the same problem.

The static variant should be better, IMO. I'm not sure whether other platforms won't face the same problem once they will start using register_platform_power_off(). I'll send the fix, thank you for the testing!

--- >8 ---

diff --git a/kernel/reboot.c b/kernel/reboot.c
index a091145ee710..4fea05d387dc 100644
--- a/kernel/reboot.c
+++ b/kernel/reboot.c
@@ -315,6 +315,37 @@ static int sys_off_notify(struct notifier_block *nb,
 	return handler->sys_off_cb(&data);
 }
 
+static struct sys_off_handler platform_sys_off_handler;
+
+static struct sys_off_handler *alloc_sys_off_handler(int priority)
+{
+	struct sys_off_handler *handler;
+
+	/*
+	 * Platforms like m68k can't allocate sys_off handler dynamically
+	 * at the early boot time.
+	 */
+	if (priority == SYS_OFF_PRIO_PLATFORM) {
+		handler = &platform_sys_off_handler;
+		if (handler->cb_data)
+			return ERR_PTR(-EBUSY);
+	} else {
+		handler = kzalloc(sizeof(*handler), GFP_KERNEL);
+		if (!handler)
+			return ERR_PTR(-ENOMEM);
+	}
+
+	return handler;
+}
+
+static void free_sys_off_handler(struct sys_off_handler *handler)
+{
+	if (handler == &platform_sys_off_handler)
+		memset(handler, 0, sizeof(*handler));
+	else
+		kfree(handler);
+}
+
 /**
  *	register_sys_off_handler - Register sys-off handler
  *	@mode: Sys-off mode
@@ -345,9 +376,9 @@ register_sys_off_handler(enum sys_off_mode mode,
 	struct sys_off_handler *handler;
 	int err;
 
-	handler = kzalloc(sizeof(*handler), GFP_KERNEL);
-	if (!handler)
-		return ERR_PTR(-ENOMEM);
+	handler = alloc_sys_off_handler(priority);
+	if (IS_ERR(handler))
+		return handler;
 
 	switch (mode) {
 	case SYS_OFF_MODE_POWER_OFF_PREPARE:
@@ -364,7 +395,7 @@ register_sys_off_handler(enum sys_off_mode mode,
 		break;
 
 	default:
-		kfree(handler);
+		free_sys_off_handler(handler);
 		return ERR_PTR(-EINVAL);
 	}
 
@@ -391,7 +422,7 @@ register_sys_off_handler(enum sys_off_mode mode,
 	}
 
 	if (err) {
-		kfree(handler);
+		free_sys_off_handler(handler);
 		return ERR_PTR(err);
 	}
 
@@ -422,7 +453,7 @@ void unregister_sys_off_handler(struct sys_off_handler *handler)
 	/* sanity check, shall never happen */
 	WARN_ON(err);
 
-	kfree(handler);
+	free_sys_off_handler(handler);
 }
 EXPORT_SYMBOL_GPL(unregister_sys_off_handler);