[PATCH 0/3] make printk work again

[PATCH 0/3] make printk work again

[Peter Zijlstra]

This basically fixes printk by evading everything it does.

There's too many problems with printk, from sleeping locks to broken console
drivers. Stop using it.

The early_console drivers are the most robust and simple, use those.

[PATCH 1/3] printk: Fix kdb_trap_printk placement

[Peter Zijlstra]

[-- Attachment #1: peterz-printk-kdb.patch --]
[-- Type: text/plain, Size: 1276 bytes --]

Some people figured vprintk_emit() makes for a nice API and exported
it, bypassing the kdb trap.

This still leaves vprintk_nmi() outside of the kbd reach, should that
be fixed too?

Cc: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/printk/printk.c |   19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1750,6 +1750,13 @@ asmlinkage int vprintk_emit(int facility
 	/* cpu currently holding logbuf_lock in this function */
 	static unsigned int logbuf_cpu = UINT_MAX;
 
+#ifdef CONFIG_KGDB_KDB
+	if (unlikely(kdb_trap_printk)) {
+		r = vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
+		return r;
+	}
+#endif
+
 	if (level == LOGLEVEL_SCHED) {
 		level = LOGLEVEL_DEFAULT;
 		in_sched = true;
@@ -1932,17 +1939,7 @@ EXPORT_SYMBOL(printk_emit);
 
 int vprintk_default(const char *fmt, va_list args)
 {
-	int r;
-
-#ifdef CONFIG_KGDB_KDB
-	if (unlikely(kdb_trap_printk)) {
-		r = vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
-		return r;
-	}
-#endif
-	r = vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);
-
-	return r;
+	return vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);
 }
 EXPORT_SYMBOL_GPL(vprintk_default);
 

[PATCH 2/3] early_printk: Add force_early_printk kernel parameter

[Peter Zijlstra]

[-- Attachment #1: peterz-force_early_printk.patch --]
[-- Type: text/plain, Size: 2661 bytes --]

Add add the 'force_early_printk' kernel parameter to override printk()
and force it into early_printk(). This bypasses all the cruft and fail
from printk() and makes things work again.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/printk/printk.c |   74 ++++++++++++++++++++++++++++++++-----------------
 1 file changed, 49 insertions(+), 25 deletions(-)

--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -344,6 +344,42 @@ __packed __aligned(4)
 #endif
 ;
 
+#ifdef CONFIG_EARLY_PRINTK
+struct console *early_console;
+
+static bool __read_mostly force_early_printk;
+
+static int __init force_early_printk_setup(char *str)
+{
+	force_early_printk = true;
+	return 0;
+}
+early_param("force_early_printk", force_early_printk_setup);
+
+static int early_vprintk(const char *fmt, va_list args)
+{
+	char buf[512];
+	int n;
+
+	n = vscnprintf(buf, sizeof(buf), fmt, args);
+	early_console->write(early_console, buf, n);
+
+	return n;
+}
+
+asmlinkage __visible void early_printk(const char *fmt, ...)
+{
+	va_list ap;
+
+	if (!early_console)
+		return;
+
+	va_start(ap, fmt);
+	early_vprintk(fmt, ap);
+	va_end(ap);
+}
+#endif
+
 /*
  * The logbuf_lock protects kmsg buffer, indices, counters.  This can be taken
  * within the scheduler's rq lock. It must be released before calling
@@ -1751,10 +1787,13 @@ asmlinkage int vprintk_emit(int facility
 	static unsigned int logbuf_cpu = UINT_MAX;
 
 #ifdef CONFIG_KGDB_KDB
-	if (unlikely(kdb_trap_printk)) {
-		r = vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
-		return r;
-	}
+	if (unlikely(kdb_trap_printk))
+		return vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
+#endif
+
+#ifdef CONFIG_EARLY_PRINTK
+	if (force_early_printk && early_console)
+		return early_vprintk(fmt, args);
 #endif
 
 	if (level == LOGLEVEL_SCHED) {
@@ -1970,7 +2009,12 @@ asmlinkage __visible int printk(const ch
 	int r;
 
 	va_start(args, fmt);
-	r = vprintk_func(fmt, args);
+#ifdef CONFIG_EARLY_PRINTK
+	if (force_early_printk && early_console)
+		r = vprintk_default(fmt, args);
+	else
+#endif
+		r = vprintk_func(fmt, args);
 	va_end(args);
 
 	return r;
@@ -2020,26 +2064,6 @@ DEFINE_PER_CPU(printk_func_t, printk_fun
 
 #endif /* CONFIG_PRINTK */
 
-#ifdef CONFIG_EARLY_PRINTK
-struct console *early_console;
-
-asmlinkage __visible void early_printk(const char *fmt, ...)
-{
-	va_list ap;
-	char buf[512];
-	int n;
-
-	if (!early_console)
-		return;
-
-	va_start(ap, fmt);
-	n = vscnprintf(buf, sizeof(buf), fmt, ap);
-	va_end(ap);
-
-	early_console->write(early_console, buf, n);
-}
-#endif
-
 static int __add_preferred_console(char *name, int idx, char *options,
 				   char *brl_options)
 {

[PATCH 3/3] early_printk: Add simple serialization to early_vprintk()

[Peter Zijlstra]

[-- Attachment #1: peterz-early_printk-serialize.patch --]
[-- Type: text/plain, Size: 978 bytes --]

In order to avoid multiple CPUs banging on the serial port at the same
time, add simple serialization. This explicitly deals with nested
contexts (like IRQs etc.).

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/printk/printk.c |   16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -356,14 +356,28 @@ static int __init force_early_printk_set
 }
 early_param("force_early_printk", force_early_printk_setup);
 
+static int early_printk_cpu = -1;
+
 static int early_vprintk(const char *fmt, va_list args)
 {
+	int n, cpu, old;
 	char buf[512];
-	int n;
+
+	cpu = get_cpu();
+	for (;;) {
+		old = cmpxchg(&early_printk_cpu, -1, cpu);
+		if (old == -1 || old == cpu)
+			break;
+
+		cpu_relax();
+	}
 
 	n = vscnprintf(buf, sizeof(buf), fmt, args);
 	early_console->write(early_console, buf, n);
 
+	smp_store_release(&early_printk_cpu, old);
+	put_cpu();
+
 	return n;
 }
 

Re: [PATCH 3/3] early_printk: Add simple serialization to early_vprintk()

[Steven Rostedt]

On Tue, 18 Oct 2016 19:08:33 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> In order to avoid multiple CPUs banging on the serial port at the same
> time, add simple serialization. This explicitly deals with nested
> contexts (like IRQs etc.).
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---

hehe, I have the exact same patch for my -rt work.

-- Steve

>  kernel/printk/printk.c |   16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -356,14 +356,28 @@ static int __init force_early_printk_set
>  }
>  early_param("force_early_printk", force_early_printk_setup);
>  
> +static int early_printk_cpu = -1;
> +
>  static int early_vprintk(const char *fmt, va_list args)
>  {
> +	int n, cpu, old;
>  	char buf[512];
> -	int n;
> +
> +	cpu = get_cpu();
> +	for (;;) {
> +		old = cmpxchg(&early_printk_cpu, -1, cpu);
> +		if (old == -1 || old == cpu)
> +			break;
> +
> +		cpu_relax();
> +	}
>  
>  	n = vscnprintf(buf, sizeof(buf), fmt, args);
>  	early_console->write(early_console, buf, n);
>  
> +	smp_store_release(&early_printk_cpu, old);
> +	put_cpu();
> +
>  	return n;
>  }
>  
> 

Re: [PATCH 3/3] early_printk: Add simple serialization to early_vprintk()

[Peter Zijlstra]

On Tue, Oct 18, 2016 at 01:19:51PM -0400, Steven Rostedt wrote:
> 
> hehe, I have the exact same patch for my -rt work.

> > +static int early_printk_cpu = -1;
> > +
> >  static int early_vprintk(const char *fmt, va_list args)
> >  {
> > +	int n, cpu, old;
> >  	char buf[512];
> > +
> > +	cpu = get_cpu();
> > +	for (;;) {
> > +		old = cmpxchg(&early_printk_cpu, -1, cpu);
> > +		if (old == -1 || old == cpu)
> > +			break;

Looking at this again, we really should not spin using cmpxchg(), that
thrashes the cacheline.

The below is slightly better spinning... then again, this isn't
performance code.

--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -376,10 +376,16 @@ static int early_vprintk(const char *fmt
 
 	cpu = get_cpu();
 	for (;;) {
-		old = cmpxchg(&early_printk_cpu, -1, cpu);
-		if (old == -1 || old == cpu)
+		old = READ_ONCE(early_printk_cpu);
+		if (old == cpu)
 			break;
 
+		if (old == -1) {
+			old = cmpxchg(&early_printk_cpu, -1, cpu);
+			if (old == -1 || old == cpu)
+				break;
+		}
+
 		cpu_relax();
 	}
 

Re: [PATCH 3/3] early_printk: Add simple serialization to early_vprintk()

[Steven Rostedt]

On Tue, 18 Oct 2016 19:30:46 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> On Tue, Oct 18, 2016 at 01:19:51PM -0400, Steven Rostedt wrote:

> Looking at this again, we really should not spin using cmpxchg(), that
> thrashes the cacheline.
> 
> The below is slightly better spinning... then again, this isn't
> performance code.

Yeah, this is similar to the hack I had.

May want to fold this in your previous version.

-- Steve

> 
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -376,10 +376,16 @@ static int early_vprintk(const char *fmt
>  
>  	cpu = get_cpu();
>  	for (;;) {
> -		old = cmpxchg(&early_printk_cpu, -1, cpu);
> -		if (old == -1 || old == cpu)
> +		old = READ_ONCE(early_printk_cpu);
> +		if (old == cpu)
>  			break;
>  
> +		if (old == -1) {
> +			old = cmpxchg(&early_printk_cpu, -1, cpu);
> +			if (old == -1 || old == cpu)
> +				break;
> +		}
> +
>  		cpu_relax();
>  	}
>  

Re: [PATCH 0/3] make printk work again

[Jan Kara]

On Tue 18-10-16 19:08:30, Peter Zijlstra wrote:
> This basically fixes printk by evading everything it does.
> 
> There's too many problems with printk, from sleeping locks to broken console
> drivers. Stop using it.

I agree that printk is fragile and your patches are likely fine for machine
where you do kernel development. However for production servers with
hundreds of SCSI LUNs assigned I don't think it is a viable solution - I'm
pretty sure those machines would take ages to boot (if they ever boot) with
early_printk implementation. So do you intend this as "the ultimate printk
solution" or just a "kernel developers debugging aid"? :)

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH 0/3] make printk work again

[Peter Zijlstra]

On Wed, Oct 19, 2016 at 09:04:16AM +0200, Jan Kara wrote:
> On Tue 18-10-16 19:08:30, Peter Zijlstra wrote:
> > This basically fixes printk by evading everything it does.
> > 
> > There's too many problems with printk, from sleeping locks to broken console
> > drivers. Stop using it.
> 
> I agree that printk is fragile and your patches are likely fine for machine
> where you do kernel development. However for production servers with
> hundreds of SCSI LUNs assigned I don't think it is a viable solution - I'm
> pretty sure those machines would take ages to boot (if they ever boot) with
> early_printk implementation. So do you intend this as "the ultimate printk
> solution" or just a "kernel developers debugging aid"? :)

Mostly just to scratch my itch. It also completely kills dmesg, which I
can't see being popular :-) On the plus side, these 3 little patches
seems like something mergable (as opposed to my previous approach which
basically just deleted everything printk). The first also fixes a real,
and long standing, issue with kdb_printk.

But I really do not see how printk and the console drivers as exist
today can ever yield something reliable. We've been stacking band-aids
on it for a while now, and I think we're at the point where we should
say stop this madness.

Either do a complete overhaul and redesign of the entire stack, or just
give up and admit its broken crap and leave it rot.

Re: [PATCH 0/3] make printk work again

[Sergey Senozhatsky]

On (10/18/16 19:08), Peter Zijlstra wrote:
> This basically fixes printk by evading everything it does.
> 
> There's too many problems with printk, from sleeping locks to broken console
> drivers. Stop using it.
> 
> The early_console drivers are the most robust and simple, use those.

ACK

Can we also please ban that pre Because it's a bit tricky.emption thing?

	-ss

Re: [PATCH 0/3] make printk work again

[Peter Zijlstra]

On Wed, Oct 19, 2016 at 08:48:28PM +0900, Sergey Senozhatsky wrote:
> On (10/18/16 19:08), Peter Zijlstra wrote:
> > This basically fixes printk by evading everything it does.
> > 
> > There's too many problems with printk, from sleeping locks to broken console
> > drivers. Stop using it.
> > 
> > The early_console drivers are the most robust and simple, use those.
> 
> ACK
> 
> Can we also please ban that pre Because it's a bit tricky.emption thing?

Ha, so that's actually quite complicated. The 3rd patch does what is
simple and robust. Doing more gets very tricky real quick.

So actual preemption is disabled per get_cpu()/put_cpu(), and cross-cpu
interleaving is disabled by that 'lock'. But interrupt (and NMI) nesting
are still possible.

It does sporadically happen, but I've not really found it to be a
problem when reading the output.

Re: [PATCH 1/3] printk: Fix kdb_trap_printk placement

[Petr Mladek]

On Tue 2016-10-18 19:08:31, Peter Zijlstra wrote:
> Some people figured vprintk_emit() makes for a nice API and exported
> it, bypassing the kdb trap.
> 
> This still leaves vprintk_nmi() outside of the kbd reach, should that
> be fixed too?

Good question! vkdb_printf() tries to avoid a deadlock but the code is racy:

int vkdb_printf(enum kdb_msgsrc src, const char *fmt, va_list ap)
{
[...]
	/* Serialize kdb_printf if multiple cpus try to write at once.
	 * But if any cpu goes recursive in kdb, just print the output,
	 * even if it is interleaved with any other text.
	 */
	if (!KDB_STATE(PRINTF_LOCK)) {
		KDB_STATE_SET(PRINTF_LOCK);
		spin_lock_irqsave(&kdb_printf_lock, flags);
		got_printf_lock = 1;
		atomic_inc(&kdb_event);
	} else {
		__acquire(kdb_printf_lock);
	}


Let's have the following situation:

CPU1					CPU2

if (!KDB_STATE(PRINTF_LOCK)) {
	KDB_STATE_SET(PRINTF_LOCK);

					if (!KDB_STATE(PRINTF_LOCK)) {
					} else {
						__acquire(kdb_printf_lock);
					}

Now, both CPUs are in the critical section and happily writing over each
other, e.g. in

	vsnprintf(next_avail, size_avail, fmt, ap);

I quess that we want to fix this race. But I am not sure if it will
be done an NMI-safe way. I am going to send a patch for this.

Well, vkdb_printf() is called later when the messages are pushed
to the main logbuffer by printk_nmi_flush_line(). It is not perfect
but...


> Cc: Jason Wessel <jason.wessel@windriver.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Otherwise, your patch makes sense:

Reviewed-by: Petr Mladek <pmladek@suse.com>

Best Regards,
Petr

Re: [PATCH 1/3] printk: Fix kdb_trap_printk placement

[Peter Zijlstra]

On Wed, Oct 19, 2016 at 04:41:40PM +0200, Petr Mladek wrote:
> On Tue 2016-10-18 19:08:31, Peter Zijlstra wrote:
> > Some people figured vprintk_emit() makes for a nice API and exported
> > it, bypassing the kdb trap.
> > 
> > This still leaves vprintk_nmi() outside of the kbd reach, should that
> > be fixed too?
> 
> Good question! vkdb_printf() tries to avoid a deadlock but the code is racy:
> 
> int vkdb_printf(enum kdb_msgsrc src, const char *fmt, va_list ap)
> {
> [...]
> 	/* Serialize kdb_printf if multiple cpus try to write at once.
> 	 * But if any cpu goes recursive in kdb, just print the output,
> 	 * even if it is interleaved with any other text.
> 	 */
> 	if (!KDB_STATE(PRINTF_LOCK)) {
> 		KDB_STATE_SET(PRINTF_LOCK);
> 		spin_lock_irqsave(&kdb_printf_lock, flags);
> 		got_printf_lock = 1;
> 		atomic_inc(&kdb_event);
> 	} else {
> 		__acquire(kdb_printf_lock);
> 	}
> 
> 
> Let's have the following situation:
> 
> CPU1					CPU2
> 
> if (!KDB_STATE(PRINTF_LOCK)) {
> 	KDB_STATE_SET(PRINTF_LOCK);
> 
> 					if (!KDB_STATE(PRINTF_LOCK)) {
> 					} else {
> 						__acquire(kdb_printf_lock);
> 					}
> 
> Now, both CPUs are in the critical section and happily writing over each
> other, e.g. in
> 
> 	vsnprintf(next_avail, size_avail, fmt, ap);
> 
> I quess that we want to fix this race. But I am not sure if it will
> be done an NMI-safe way. I am going to send a patch for this.

Something like patch 3 in this series should do I suppose. But the
vkdb_printf() thing using spin_lock_irqsave() seems to suggest it was
never meant to be used from NMI context.

Re: [PATCH 1/3] printk: Fix kdb_trap_printk placement

[Sergey Senozhatsky]

On (10/18/16 19:08), Peter Zijlstra wrote:
> 
> Some people figured vprintk_emit() makes for a nice API and exported
> it, bypassing the kdb trap.
> 
> This still leaves vprintk_nmi() outside of the kbd reach, should that
> be fixed too?
> 
> Cc: Jason Wessel <jason.wessel@windriver.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

looks good to me.

Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

	-ss

Re: [PATCH 1/3] printk: Fix kdb_trap_printk placement

[Petr Mladek]

On Tue 2016-10-18 19:08:31, Peter Zijlstra wrote:
> Some people figured vprintk_emit() makes for a nice API and exported
> it, bypassing the kdb trap.

I think that nobody saw this problem because kdb_trap_printk was
used only for a limited number of printk's. It is just a trick
how to use generic functions to print messages in the kdb context,
e.g. for getting backtraces.

But the patch makes sense.


> This still leaves vprintk_nmi() outside of the kbd reach, should that
> be fixed too?

It is perfectly fine. Messages from NMI context are not meant for
kdb anyway.

> Cc: Jason Wessel <jason.wessel@windriver.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  kernel/printk/printk.c |   19 ++++++++-----------
>  1 file changed, 8 insertions(+), 11 deletions(-)
> 
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -1750,6 +1750,13 @@ asmlinkage int vprintk_emit(int facility
>  	/* cpu currently holding logbuf_lock in this function */
>  	static unsigned int logbuf_cpu = UINT_MAX;
>  
> +#ifdef CONFIG_KGDB_KDB
> +	if (unlikely(kdb_trap_printk)) {
> +		r = vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
> +		return r;

r is not defined. It is fixed in the next patch but it breaks
bisectability.

Please, find below an updated patch that also includes
my Reviewed-by.


>From 5adf18de45ba986ea3ae611446828238f4d65fe0 Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
Date: Tue, 18 Oct 2016 19:08:31 +0200
Subject: [PATCH 1/3] printk: Fix kdb_trap_printk placement

Some people figured vprintk_emit() makes for a nice API and exported
it, bypassing the kdb trap.

This still leaves vprintk_nmi() outside of the kbd reach, should that
be fixed too?

Cc: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 kernel/printk/printk.c | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index f7a55e9ff2f7..541ce7705353 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1781,6 +1781,11 @@ asmlinkage int vprintk_emit(int facility, int level,
 	/* cpu currently holding logbuf_lock in this function */
 	static unsigned int logbuf_cpu = UINT_MAX;
 
+#ifdef CONFIG_KGDB_KDB
+	if (unlikely(kdb_trap_printk))
+		return vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
+#endif
+
 	if (level == LOGLEVEL_SCHED) {
 		level = LOGLEVEL_DEFAULT;
 		in_sched = true;
@@ -1923,17 +1928,7 @@ asmlinkage int printk_emit(int facility, int level,
 
 int vprintk_default(const char *fmt, va_list args)
 {
-	int r;
-
-#ifdef CONFIG_KGDB_KDB
-	if (unlikely(kdb_trap_printk)) {
-		r = vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
-		return r;
-	}
-#endif
-	r = vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);
-
-	return r;
+	return vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);
 }
 EXPORT_SYMBOL_GPL(vprintk_default);
 
-- 
1.8.5.6

Re: [PATCH 2/3] early_printk: Add force_early_printk kernel parameter

[Petr Mladek]

On Tue 2016-10-18 19:08:32, Peter Zijlstra wrote:
> Add add the 'force_early_printk' kernel parameter to override printk()
> and force it into early_printk(). This bypasses all the cruft and fail
> from printk() and makes things work again.

IMHO, the patch makes perfect sense and helps with debugging
hard problems.

> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -1751,10 +1787,13 @@ asmlinkage int vprintk_emit(int facility
>  	static unsigned int logbuf_cpu = UINT_MAX;
>  
>  #ifdef CONFIG_KGDB_KDB
> -	if (unlikely(kdb_trap_printk)) {
> -		r = vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
> -		return r;
> -	}
> +	if (unlikely(kdb_trap_printk))
> +		return vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
> +#endif

Please, find below an updated patch that has also my Reviewed-by.

In particular, the above change was moved to the first patch
to fix bisectability. The result after applying both patches
is still exactly the same.


>From e1c00ae67d07767ec8e5bddb1113c2badf31f4bd Mon Sep 17 00:00:00 2001
From: Petr Mladek <pmladek@suse.com>
Date: Tue, 29 Nov 2016 13:32:56 +0100
Subject: [PATCH 2/3] early_printk: Add force_early_printk kernel parameter

Add add the 'force_early_printk' kernel parameter to override printk()
and force it into early_printk(). This bypasses all the cruft and fail
from printk() and makes things work again.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 kernel/printk/printk.c | 68 ++++++++++++++++++++++++++++++++++----------------
 1 file changed, 47 insertions(+), 21 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 541ce7705353..bb612e5c2e00 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -344,6 +344,42 @@ __packed __aligned(4)
 #endif
 ;
 
+#ifdef CONFIG_EARLY_PRINTK
+struct console *early_console;
+
+static bool __read_mostly force_early_printk;
+
+static int __init force_early_printk_setup(char *str)
+{
+	force_early_printk = true;
+	return 0;
+}
+early_param("force_early_printk", force_early_printk_setup);
+
+static int early_vprintk(const char *fmt, va_list args)
+{
+	char buf[512];
+	int n;
+
+	n = vscnprintf(buf, sizeof(buf), fmt, args);
+	early_console->write(early_console, buf, n);
+
+	return n;
+}
+
+asmlinkage __visible void early_printk(const char *fmt, ...)
+{
+	va_list ap;
+
+	if (!early_console)
+		return;
+
+	va_start(ap, fmt);
+	early_vprintk(fmt, ap);
+	va_end(ap);
+}
+#endif
+
 /*
  * The logbuf_lock protects kmsg buffer, indices, counters.  This can be taken
  * within the scheduler's rq lock. It must be released before calling
@@ -1786,6 +1822,11 @@ asmlinkage int vprintk_emit(int facility, int level,
 		return vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
 #endif
 
+#ifdef CONFIG_EARLY_PRINTK
+	if (force_early_printk && early_console)
+		return early_vprintk(fmt, args);
+#endif
+
 	if (level == LOGLEVEL_SCHED) {
 		level = LOGLEVEL_DEFAULT;
 		in_sched = true;
@@ -1959,7 +2000,12 @@ asmlinkage __visible int printk(const char *fmt, ...)
 	int r;
 
 	va_start(args, fmt);
-	r = vprintk_func(fmt, args);
+#ifdef CONFIG_EARLY_PRINTK
+	if (force_early_printk && early_console)
+		r = vprintk_default(fmt, args);
+	else
+#endif
+		r = vprintk_func(fmt, args);
 	va_end(args);
 
 	return r;
@@ -2009,26 +2055,6 @@ static size_t msg_print_text(const struct printk_log *msg, enum log_flags prev,
 
 #endif /* CONFIG_PRINTK */
 
-#ifdef CONFIG_EARLY_PRINTK
-struct console *early_console;
-
-asmlinkage __visible void early_printk(const char *fmt, ...)
-{
-	va_list ap;
-	char buf[512];
-	int n;
-
-	if (!early_console)
-		return;
-
-	va_start(ap, fmt);
-	n = vscnprintf(buf, sizeof(buf), fmt, ap);
-	va_end(ap);
-
-	early_console->write(early_console, buf, n);
-}
-#endif
-
 static int __add_preferred_console(char *name, int idx, char *options,
 				   char *brl_options)
 {
-- 
1.8.5.6

Re: [PATCH 3/3] early_printk: Add simple serialization to early_vprintk()

[Petr Mladek]

On Tue 2016-10-18 19:08:33, Peter Zijlstra wrote:
> In order to avoid multiple CPUs banging on the serial port at the same
> time, add simple serialization. This explicitly deals with nested
> contexts (like IRQs etc.).
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Makes sense. Just a small comment below.

Reviewd-by: Petr Mladek <pmladek@suse.com>

> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -356,14 +356,28 @@ static int __init force_early_printk_set
>  }
>  early_param("force_early_printk", force_early_printk_setup);
>  
> +static int early_printk_cpu = -1;

[...]

> +	for (;;) {
> +		old = cmpxchg(&early_printk_cpu, -1, cpu);
> +		if (old == -1 || old == cpu)
> +			break;
> +
> +		cpu_relax();
> +	}
>  
>  	n = vscnprintf(buf, sizeof(buf), fmt, args);
>  	early_console->write(early_console, buf, n);
>  
> +	smp_store_release(&early_printk_cpu, old);

checkpatch.pl complains about using a barrier without a comment.
The code is simple but it still might help to add something like:

	/* Releasing early_printk_cpu custom lock. */

Best Regards,
Petr

Re: [PATCH 2/3] early_printk: Add force_early_printk kernel parameter

[Steven Rostedt]

On Fri, 13 Oct 2017 15:06:09 +0200
Petr Mladek <pmladek@suse.com> wrote:
> > 
> > Can we even have !PRINTK && EARLY_PRINTK? If so it seems to me continued
> > usage of early_printk() is what makes most sense.  
> 
> Yes, !PRINTK && EARLY_PRINTK is possible at the moment. It makes some
> sense because EARLY_PRINTK needs only consoles and they are needed
> also for !PRINTK stuff.
> 
> We either should define force_early_printk only when
> PRINTK is enabled.

I think it makes sense to have force_early_printk depend on PRINTK and
EARLY_PRINTK.

 
> > The reason I did it like this and not use that function pointer thing is
> > that I didn't want to risk anybody hijacking my output ever.  
> 
> I understand. I think about refactoring the code so that all
> *printk*() variants call printk_func(). This function
> could then call the right printk implementation according
> to the context or global setting.
> 
> This way we could have all the logic on a single place and
> avoid the race.
> 
> Note that printk_func() is not longer a pointer. It is
> a function since the commit 099f1c84c0052ec1b2
> ("printk: introduce per-cpu safe_print seq buffer").

Yes, I agree with Petr here. Slapping the force printk into
printk_func() should have the same effect, as everything is hard coded
now:

asmlinkage __visible int printk(const char *fmt, ...)
{
	va_list args;
	int r;

	va_start(args, fmt);
	r = vprintk_func(fmt, args);
	va_end(args);

	return r;
}


__printf(1, 0) int vprintk_func(const char *fmt, va_list args)
{
	/* Use extra buffer in NMI when logbuf_lock is taken or in safe mode. */
	if (this_cpu_read(printk_context) & PRINTK_NMI_CONTEXT_MASK)
		return vprintk_nmi(fmt, args);

	/* Use extra buffer to prevent a recursion deadlock in safe mode. */
	if (this_cpu_read(printk_context) & PRINTK_SAFE_CONTEXT_MASK)
		return vprintk_safe(fmt, args);

	/*
	 * Use the main logbuf when logbuf_lock is available in NMI.
	 * But avoid calling console drivers that might have their own locks.
	 */
	if (this_cpu_read(printk_context) & PRINTK_NMI_DEFERRED_CONTEXT_MASK)
		return vprintk_deferred(fmt, args);

	/* No obstacles. */
	return vprintk_default(fmt, args);
}

Thus putting in the call to early_printk() at the very beginning of
vprintk_func() would have the result that Peter would like.

-- Steve

Re: [PATCH 2/3] early_printk: Add force_early_printk kernel parameter

[Peter Zijlstra]

On Fri, Oct 13, 2017 at 03:06:09PM +0200, Petr Mladek wrote:

> Or we should call early_printk() from printk() also when
> PRINTK is disabled.

This.

> > Do you mean if someone were to toggle force_early_printk at runtime?
> 
> Or that someone unregisters the early console.

That's broken anyway, nor do I think anybody does that, early_printk is
a set once never touch kinda thing.

Re: [PATCH 2/3] early_printk: Add force_early_printk kernel parameter

[Petr Mladek]

On Thu 2017-10-12 13:39:49, Peter Zijlstra wrote:
> On Thu, Oct 12, 2017 at 12:24:19PM +0200, Petr Mladek wrote:
> > On Thu 2017-09-28 14:18:25, Peter Zijlstra wrote:
> 
> > > +#ifdef CONFIG_EARLY_PRINTK
> > > +struct console *early_console;
> > > +
> > > +static bool __read_mostly force_early_printk;
> > > +
> > > +static int __init force_early_printk_setup(char *str)
> > > +{
> > > +	force_early_printk = true;
> > > +	return 0;
> > > +}
> > > +early_param("force_early_printk", force_early_printk_setup);
> > 
> > The parameter is currently used only when CONFIG_PRINTK is enabled.
> > But CONFIG_EARLY_PRINTK is independent. What would be your preferred
> > behavior when CONFIG_PRINTK is disabled, please?
> 
> Can we even have !PRINTK && EARLY_PRINTK? If so it seems to me continued
> usage of early_printk() is what makes most sense.

Yes, !PRINTK && EARLY_PRINTK is possible at the moment. It makes some
sense because EARLY_PRINTK needs only consoles and they are needed
also for !PRINTK stuff.

We either should define force_early_printk only when
PRINTK is enabled.

Or we should call early_printk() from printk() also when
PRINTK is disabled. The current implemetation is in
include/linux/printk.h, see

static inline __printf(1, 2) __cold
int printk(const char *s, ...)
{
	return 0;
}

> > > @@ -1816,6 +1852,11 @@ asmlinkage int vprintk_emit(int facility
> > >  		return vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
> > >  #endif
> > >  
> > > +#ifdef CONFIG_EARLY_PRINTK
> > > +	if (force_early_printk && early_console)
> > > +		return early_vprintk(fmt, args);
> > > +#endif
> > > +
> > >  	if (level == LOGLEVEL_SCHED) {
> > >  		level = LOGLEVEL_DEFAULT;
> > >  		in_sched = true;
> > > @@ -1939,7 +1980,12 @@ asmlinkage __visible int printk(const ch
> > >  	int r;
> > >  
> > >  	va_start(args, fmt);
> > > -	r = vprintk_func(fmt, args);
> > > +#ifdef CONFIG_EARLY_PRINTK
> > > +	if (force_early_printk && early_console)
> > > +		r = vprintk_default(fmt, args);
> > > +	else
> > > +#endif
> > > +		r = vprintk_func(fmt, args);
> > 
> > There is rather theoretical race. We skip vprintk_func() because
> > we believe that vprintk_default()/vprintk_emit() would choose
> > handle this by early_printk().
> 
> Do you mean if someone were to toggle force_early_printk at runtime?

Or that someone unregisters the early console.


> The reason I did it like this and not use that function pointer thing is
> that I didn't want to risk anybody hijacking my output ever.

I understand. I think about refactoring the code so that all
*printk*() variants call printk_func(). This function
could then call the right printk implementation according
to the context or global setting.

This way we could have all the logic on a single place and
avoid the race.

Note that printk_func() is not longer a pointer. It is
a function since the commit 099f1c84c0052ec1b2
("printk: introduce per-cpu safe_print seq buffer").

Best Regards,
Petr

Re: [PATCH 2/3] early_printk: Add force_early_printk kernel parameter

[Peter Zijlstra]

On Thu, Oct 12, 2017 at 12:24:19PM +0200, Petr Mladek wrote:
> On Thu 2017-09-28 14:18:25, Peter Zijlstra wrote:

> > +#ifdef CONFIG_EARLY_PRINTK
> > +struct console *early_console;
> > +
> > +static bool __read_mostly force_early_printk;
> > +
> > +static int __init force_early_printk_setup(char *str)
> > +{
> > +	force_early_printk = true;
> > +	return 0;
> > +}
> > +early_param("force_early_printk", force_early_printk_setup);
> 
> The parameter is currently used only when CONFIG_PRINTK is enabled.
> But CONFIG_EARLY_PRINTK is independent. What would be your preferred
> behavior when CONFIG_PRINTK is disabled, please?

Can we even have !PRINTK && EARLY_PRINTK? If so it seems to me continued
usage of early_printk() is what makes most sense.

> > @@ -1816,6 +1852,11 @@ asmlinkage int vprintk_emit(int facility
> >  		return vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
> >  #endif
> >  
> > +#ifdef CONFIG_EARLY_PRINTK
> > +	if (force_early_printk && early_console)
> > +		return early_vprintk(fmt, args);
> > +#endif
> > +
> >  	if (level == LOGLEVEL_SCHED) {
> >  		level = LOGLEVEL_DEFAULT;
> >  		in_sched = true;
> > @@ -1939,7 +1980,12 @@ asmlinkage __visible int printk(const ch
> >  	int r;
> >  
> >  	va_start(args, fmt);
> > -	r = vprintk_func(fmt, args);
> > +#ifdef CONFIG_EARLY_PRINTK
> > +	if (force_early_printk && early_console)
> > +		r = vprintk_default(fmt, args);
> > +	else
> > +#endif
> > +		r = vprintk_func(fmt, args);
> 
> There is rather theoretical race. We skip vprintk_func() because
> we believe that vprintk_default()/vprintk_emit() would choose
> handle this by early_printk().

Do you mean if someone were to toggle force_early_printk at runtime?

The reason I did it like this and not use that function pointer thing is
that I didn't want to risk anybody hijacking my output ever.

Re: [PATCH 2/3] early_printk: Add force_early_printk kernel parameter

[Petr Mladek]

On Thu 2017-09-28 14:18:25, Peter Zijlstra wrote:
> Add add the 'force_early_printk' kernel parameter to override printk()
> and force it into early_printk(). This bypasses all the cruft and fail
> from printk() and makes things work again.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  kernel/printk/printk.c |   68 +++++++++++++++++++++++++++++++++----------------
>  1 file changed, 47 insertions(+), 21 deletions(-)
> 
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -365,6 +365,42 @@ __packed __aligned(4)
>  #endif
>  ;
>  
> +#ifdef CONFIG_EARLY_PRINTK
> +struct console *early_console;
> +
> +static bool __read_mostly force_early_printk;
> +
> +static int __init force_early_printk_setup(char *str)
> +{
> +	force_early_printk = true;
> +	return 0;
> +}
> +early_param("force_early_printk", force_early_printk_setup);

The parameter is currently used only when CONFIG_PRINTK is enabled.
But CONFIG_EARLY_PRINTK is independent. What would be your preferred
behavior when CONFIG_PRINTK is disabled, please?


> @@ -1816,6 +1852,11 @@ asmlinkage int vprintk_emit(int facility
>  		return vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
>  #endif
>  
> +#ifdef CONFIG_EARLY_PRINTK
> +	if (force_early_printk && early_console)
> +		return early_vprintk(fmt, args);
> +#endif
> +
>  	if (level == LOGLEVEL_SCHED) {
>  		level = LOGLEVEL_DEFAULT;
>  		in_sched = true;
> @@ -1939,7 +1980,12 @@ asmlinkage __visible int printk(const ch
>  	int r;
>  
>  	va_start(args, fmt);
> -	r = vprintk_func(fmt, args);
> +#ifdef CONFIG_EARLY_PRINTK
> +	if (force_early_printk && early_console)
> +		r = vprintk_default(fmt, args);
> +	else
> +#endif
> +		r = vprintk_func(fmt, args);

There is rather theoretical race. We skip vprintk_func() because
we believe that vprintk_default()/vprintk_emit() would choose
handle this by early_printk().

A solution would be the clean up of the exported printk() interfaces
that I suggested in the other mail. Then we could choose the right
implementation on a single place: printk_func().

PeterZ, I guess that you do not want to spend much time on this.
But if you basically agree with my proposal, I could start
working on it and rebase this patchset on top of it.

Best Regards,
Petr

PS: I am sorry that I am complicating this rather simple patchset.
I only want to be careful. You know that the current printk code
is a mess and I would like to improve it.

Re: [PATCH 2/3] early_printk: Add force_early_printk kernel parameter

[Steven Rostedt]

On Thu, 28 Sep 2017 14:18:25 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> Add add the 'force_early_printk' kernel parameter to override printk()
> and force it into early_printk(). This bypasses all the cruft and fail
> from printk() and makes things work again.

Probably break this up into two patches. One for creation of
early_vprintk(), and the other to add the force_early_printk parameter.

-- Steve

> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  kernel/printk/printk.c |   68 +++++++++++++++++++++++++++++++++----------------
>  1 file changed, 47 insertions(+), 21 deletions(-)
> 
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -365,6 +365,42 @@ __packed __aligned(4)
>  #endif
>  ;
>  
> +#ifdef CONFIG_EARLY_PRINTK
> +struct console *early_console;
> +
> +static bool __read_mostly force_early_printk;
> +
> +static int __init force_early_printk_setup(char *str)
> +{
> +	force_early_printk = true;
> +	return 0;
> +}
> +early_param("force_early_printk", force_early_printk_setup);
> +
> +static int early_vprintk(const char *fmt, va_list args)
> +{
> +	char buf[512];
> +	int n;
> +
> +	n = vscnprintf(buf, sizeof(buf), fmt, args);
> +	early_console->write(early_console, buf, n);
> +
> +	return n;
> +}
> +
> +asmlinkage __visible void early_printk(const char *fmt, ...)
> +{
> +	va_list ap;
> +
> +	if (!early_console)
> +		return;
> +
> +	va_start(ap, fmt);
> +	early_vprintk(fmt, ap);
> +	va_end(ap);
> +}
> +#endif
> +
>  /*
>   * The logbuf_lock protects kmsg buffer, indices, counters.  This can be taken
>   * within the scheduler's rq lock. It must be released before calling
> @@ -1816,6 +1852,11 @@ asmlinkage int vprintk_emit(int facility
>  		return vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
>  #endif
>  
> +#ifdef CONFIG_EARLY_PRINTK
> +	if (force_early_printk && early_console)
> +		return early_vprintk(fmt, args);
> +#endif
> +
>  	if (level == LOGLEVEL_SCHED) {
>  		level = LOGLEVEL_DEFAULT;
>  		in_sched = true;
> @@ -1939,7 +1980,12 @@ asmlinkage __visible int printk(const ch
>  	int r;
>  
>  	va_start(args, fmt);
> -	r = vprintk_func(fmt, args);
> +#ifdef CONFIG_EARLY_PRINTK
> +	if (force_early_printk && early_console)
> +		r = vprintk_default(fmt, args);
> +	else
> +#endif
> +		r = vprintk_func(fmt, args);
>  	va_end(args);
>  
>  	return r;
> @@ -1975,26 +2021,6 @@ static size_t msg_print_text(const struc
>  static bool suppress_message_printing(int level) { return false; }
>  #endif /* CONFIG_PRINTK */
>  
> -#ifdef CONFIG_EARLY_PRINTK
> -struct console *early_console;
> -
> -asmlinkage __visible void early_printk(const char *fmt, ...)
> -{
> -	va_list ap;
> -	char buf[512];
> -	int n;
> -
> -	if (!early_console)
> -		return;
> -
> -	va_start(ap, fmt);
> -	n = vscnprintf(buf, sizeof(buf), fmt, ap);
> -	va_end(ap);
> -
> -	early_console->write(early_console, buf, n);
> -}
> -#endif
> -
>  static int __add_preferred_console(char *name, int idx, char *options,
>  				   char *brl_options)
>  {
> 

Re: [PATCH 2/3] early_printk: Add force_early_printk kernel parameter

[Randy Dunlap]

On 09/28/17 09:07, Peter Zijlstra wrote:
> On Thu, Sep 28, 2017 at 08:41:37AM -0700, Randy Dunlap wrote:
> 
>> Please add that kernel parameter to Documentation/admin-guide/kernel-parameters.txt.
> 
> Something like so?

Yes, thanks. Ack.

> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1165,6 +1165,11 @@
>  			parameter will force ia64_sal_cache_flush to call
>  			ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
>  
> +	force_early_printk
> +			Forcefully uses early_console (as per earlyprintk=)
> +			usage for regular printk, bypassing everything,
> +			including the syslog (dmesg will be empty).
> +
>  	forcepae [X86-32]
>  			Forcefully enable Physical Address Extension (PAE).
>  			Many Pentium M systems disable PAE but may have a
> 


-- 
~Randy

Re: [PATCH 2/3] early_printk: Add force_early_printk kernel parameter

[Peter Zijlstra]

On Thu, Sep 28, 2017 at 08:41:37AM -0700, Randy Dunlap wrote:

> Please add that kernel parameter to Documentation/admin-guide/kernel-parameters.txt.

Something like so?

--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1165,6 +1165,11 @@
 			parameter will force ia64_sal_cache_flush to call
 			ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
 
+	force_early_printk
+			Forcefully uses early_console (as per earlyprintk=)
+			usage for regular printk, bypassing everything,
+			including the syslog (dmesg will be empty).
+
 	forcepae [X86-32]
 			Forcefully enable Physical Address Extension (PAE).
 			Many Pentium M systems disable PAE but may have a

Re: [PATCH 2/3] early_printk: Add force_early_printk kernel parameter

[Randy Dunlap]

On 09/28/17 05:18, Peter Zijlstra wrote:

<attachment not shown>

Hi Peter,

Please add that kernel parameter to Documentation/admin-guide/kernel-parameters.txt.

thanks,
-- 
~Randy

[PATCH 2/3] early_printk: Add force_early_printk kernel parameter

[Peter Zijlstra]

[-- Attachment #1: peterz-force_early_printk.patch --]
[-- Type: text/plain, Size: 2569 bytes --]

Add add the 'force_early_printk' kernel parameter to override printk()
and force it into early_printk(). This bypasses all the cruft and fail
from printk() and makes things work again.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/printk/printk.c |   68 +++++++++++++++++++++++++++++++++----------------
 1 file changed, 47 insertions(+), 21 deletions(-)

--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -365,6 +365,42 @@ __packed __aligned(4)
 #endif
 ;
 
+#ifdef CONFIG_EARLY_PRINTK
+struct console *early_console;
+
+static bool __read_mostly force_early_printk;
+
+static int __init force_early_printk_setup(char *str)
+{
+	force_early_printk = true;
+	return 0;
+}
+early_param("force_early_printk", force_early_printk_setup);
+
+static int early_vprintk(const char *fmt, va_list args)
+{
+	char buf[512];
+	int n;
+
+	n = vscnprintf(buf, sizeof(buf), fmt, args);
+	early_console->write(early_console, buf, n);
+
+	return n;
+}
+
+asmlinkage __visible void early_printk(const char *fmt, ...)
+{
+	va_list ap;
+
+	if (!early_console)
+		return;
+
+	va_start(ap, fmt);
+	early_vprintk(fmt, ap);
+	va_end(ap);
+}
+#endif
+
 /*
  * The logbuf_lock protects kmsg buffer, indices, counters.  This can be taken
  * within the scheduler's rq lock. It must be released before calling
@@ -1816,6 +1852,11 @@ asmlinkage int vprintk_emit(int facility
 		return vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
 #endif
 
+#ifdef CONFIG_EARLY_PRINTK
+	if (force_early_printk && early_console)
+		return early_vprintk(fmt, args);
+#endif
+
 	if (level == LOGLEVEL_SCHED) {
 		level = LOGLEVEL_DEFAULT;
 		in_sched = true;
@@ -1939,7 +1980,12 @@ asmlinkage __visible int printk(const ch
 	int r;
 
 	va_start(args, fmt);
-	r = vprintk_func(fmt, args);
+#ifdef CONFIG_EARLY_PRINTK
+	if (force_early_printk && early_console)
+		r = vprintk_default(fmt, args);
+	else
+#endif
+		r = vprintk_func(fmt, args);
 	va_end(args);
 
 	return r;
@@ -1975,26 +2021,6 @@ static size_t msg_print_text(const struc
 static bool suppress_message_printing(int level) { return false; }
 #endif /* CONFIG_PRINTK */
 
-#ifdef CONFIG_EARLY_PRINTK
-struct console *early_console;
-
-asmlinkage __visible void early_printk(const char *fmt, ...)
-{
-	va_list ap;
-	char buf[512];
-	int n;
-
-	if (!early_console)
-		return;
-
-	va_start(ap, fmt);
-	n = vscnprintf(buf, sizeof(buf), fmt, ap);
-	va_end(ap);
-
-	early_console->write(early_console, buf, n);
-}
-#endif
-
 static int __add_preferred_console(char *name, int idx, char *options,
 				   char *brl_options)
 {