[PATCH 1/2] powerpc: Use seq_buf to avoid pr_cont() in __die()

[PATCH 1/2] powerpc: Use seq_buf to avoid pr_cont() in __die()

[Michael Ellerman]

Using pr_cont() risks having our output interleaved with other output
from other CPUs. Instead use a seq_buf to construct the line and then
print it as a whole.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
 arch/powerpc/kernel/traps.c | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 64936b60d521..431a86d3f772 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -38,6 +38,7 @@
 #include <linux/kdebug.h>
 #include <linux/ratelimit.h>
 #include <linux/context_tracking.h>
+#include <linux/seq_buf.h>
 #include <linux/smp.h>
 #include <linux/console.h>
 #include <linux/kmsg_dump.h>
@@ -255,26 +256,34 @@ NOKPROBE_SYMBOL(oops_end);
 
 static int __die(const char *str, struct pt_regs *regs, long err)
 {
+	char buf[128]; /* enough for all flags and a long platform name */
+	struct seq_buf s;
+
+	seq_buf_init(&s, buf, sizeof(buf));
+
 	printk("Oops: %s, sig: %ld [#%d]\n", str, err, ++die_counter);
 
 	if (IS_ENABLED(CONFIG_CPU_LITTLE_ENDIAN))
-		printk("LE ");
+		seq_buf_puts(&s, "LE ");
 	else
-		printk("BE ");
+		seq_buf_puts(&s, "BE ");
 
 	if (IS_ENABLED(CONFIG_PREEMPT))
-		pr_cont("PREEMPT ");
+		seq_buf_puts(&s, "PREEMPT ");
 
 	if (IS_ENABLED(CONFIG_SMP))
-		pr_cont("SMP NR_CPUS=%d ", NR_CPUS);
+		seq_buf_printf(&s, "SMP NR_CPUS=%d ", NR_CPUS);
 
 	if (debug_pagealloc_enabled())
-		pr_cont("DEBUG_PAGEALLOC ");
+		seq_buf_puts(&s, "DEBUG_PAGEALLOC ");
 
 	if (IS_ENABLED(CONFIG_NUMA))
-		pr_cont("NUMA ");
+		seq_buf_puts(&s, "NUMA ");
+
+	if (ppc_md.name)
+		seq_buf_puts(&s, ppc_md.name);
 
-	pr_cont("%s\n", ppc_md.name ? ppc_md.name : "");
+	printk("%s\n", buf);
 
 	if (notify_die(DIE_OOPS, str, regs, err, 255, SIGSEGV) == NOTIFY_STOP)
 		return 1;
-- 
2.20.1

[PATCH 2/2] powerpc: Show PAGE_SIZE in __die() output

[Michael Ellerman]

The page size the kernel is built with is useful info when debugging a
crash, so add it to the output in __die().

Result looks like eg:

  kernel BUG at drivers/misc/lkdtm/bugs.c:63!
  Oops: Exception in kernel mode, sig: 5 [#1]
  LE PAGE_SIZE=64K SMP NR_CPUS=2048 NUMA pSeries
  Modules linked in: vmx_crypto kvm binfmt_misc ip_tables

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
 arch/powerpc/kernel/traps.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 431a86d3f772..fc972e4eee5f 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -268,6 +268,18 @@ static int __die(const char *str, struct pt_regs *regs, long err)
 	else
 		seq_buf_puts(&s, "BE ");
 
+	seq_buf_puts(&s, "PAGE_SIZE=");
+	if (IS_ENABLED(CONFIG_PPC_4K_PAGES))
+		seq_buf_puts(&s, "4K ");
+	else if (IS_ENABLED(CONFIG_PPC_16K_PAGES))
+		seq_buf_puts(&s, "16K ");
+	else if (IS_ENABLED(CONFIG_PPC_64K_PAGES))
+		seq_buf_puts(&s, "64K ");
+	else if (IS_ENABLED(CONFIG_PPC_256K_PAGES))
+		seq_buf_puts(&s, "256K ");
+	else
+		BUILD_BUG_ON(1);
+
 	if (IS_ENABLED(CONFIG_PREEMPT))
 		seq_buf_puts(&s, "PREEMPT ");
 
-- 
2.20.1

Re: [PATCH 1/2] powerpc: Use seq_buf to avoid pr_cont() in __die()

[Christophe Leroy]

Le 08/01/2019 à 13:04, Michael Ellerman a écrit :
> Using pr_cont() risks having our output interleaved with other output
> from other CPUs. Instead use a seq_buf to construct the line and then
> print it as a whole.

Why not simply doing a single printk() or similar on the same model as 
X86 for instance ? 
(https://elixir.bootlin.com/linux/v5.0-rc1/source/arch/x86/kernel/dumpstack.c#L368)

Christophe

> 
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
> ---
>   arch/powerpc/kernel/traps.c | 23 ++++++++++++++++-------
>   1 file changed, 16 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
> index 64936b60d521..431a86d3f772 100644
> --- a/arch/powerpc/kernel/traps.c
> +++ b/arch/powerpc/kernel/traps.c
> @@ -38,6 +38,7 @@
>   #include <linux/kdebug.h>
>   #include <linux/ratelimit.h>
>   #include <linux/context_tracking.h>
> +#include <linux/seq_buf.h>
>   #include <linux/smp.h>
>   #include <linux/console.h>
>   #include <linux/kmsg_dump.h>
> @@ -255,26 +256,34 @@ NOKPROBE_SYMBOL(oops_end);
>   
>   static int __die(const char *str, struct pt_regs *regs, long err)
>   {
> +	char buf[128]; /* enough for all flags and a long platform name */
> +	struct seq_buf s;
> +
> +	seq_buf_init(&s, buf, sizeof(buf));
> +
>   	printk("Oops: %s, sig: %ld [#%d]\n", str, err, ++die_counter);
>   
>   	if (IS_ENABLED(CONFIG_CPU_LITTLE_ENDIAN))
> -		printk("LE ");
> +		seq_buf_puts(&s, "LE ");
>   	else
> -		printk("BE ");
> +		seq_buf_puts(&s, "BE ");
>   
>   	if (IS_ENABLED(CONFIG_PREEMPT))
> -		pr_cont("PREEMPT ");
> +		seq_buf_puts(&s, "PREEMPT ");
>   
>   	if (IS_ENABLED(CONFIG_SMP))
> -		pr_cont("SMP NR_CPUS=%d ", NR_CPUS);
> +		seq_buf_printf(&s, "SMP NR_CPUS=%d ", NR_CPUS);
>   
>   	if (debug_pagealloc_enabled())
> -		pr_cont("DEBUG_PAGEALLOC ");
> +		seq_buf_puts(&s, "DEBUG_PAGEALLOC ");
>   
>   	if (IS_ENABLED(CONFIG_NUMA))
> -		pr_cont("NUMA ");
> +		seq_buf_puts(&s, "NUMA ");
> +
> +	if (ppc_md.name)
> +		seq_buf_puts(&s, ppc_md.name);
>   
> -	pr_cont("%s\n", ppc_md.name ? ppc_md.name : "");
> +	printk("%s\n", buf);
>   
>   	if (notify_die(DIE_OOPS, str, regs, err, 255, SIGSEGV) == NOTIFY_STOP)
>   		return 1;
> 

Re: [PATCH 2/2] powerpc: Show PAGE_SIZE in __die() output

[Christophe Leroy]

Le 08/01/2019 à 13:05, Michael Ellerman a écrit :
> The page size the kernel is built with is useful info when debugging a
> crash, so add it to the output in __die().
> 
> Result looks like eg:
> 
>    kernel BUG at drivers/misc/lkdtm/bugs.c:63!
>    Oops: Exception in kernel mode, sig: 5 [#1]
>    LE PAGE_SIZE=64K SMP NR_CPUS=2048 NUMA pSeries
>    Modules linked in: vmx_crypto kvm binfmt_misc ip_tables
> 
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
> ---
>   arch/powerpc/kernel/traps.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
> index 431a86d3f772..fc972e4eee5f 100644
> --- a/arch/powerpc/kernel/traps.c
> +++ b/arch/powerpc/kernel/traps.c
> @@ -268,6 +268,18 @@ static int __die(const char *str, struct pt_regs *regs, long err)
>   	else
>   		seq_buf_puts(&s, "BE ");
>   
> +	seq_buf_puts(&s, "PAGE_SIZE=");
> +	if (IS_ENABLED(CONFIG_PPC_4K_PAGES))
> +		seq_buf_puts(&s, "4K ");
> +	else if (IS_ENABLED(CONFIG_PPC_16K_PAGES))
> +		seq_buf_puts(&s, "16K ");
> +	else if (IS_ENABLED(CONFIG_PPC_64K_PAGES))
> +		seq_buf_puts(&s, "64K ");
> +	else if (IS_ENABLED(CONFIG_PPC_256K_PAGES))
> +		seq_buf_puts(&s, "256K ");

Can't we build all the above at once using PAGE_SHIFT ?

Something like (untested):

"%dK ", 1 << (PAGE_SHIFT - 10)

Christophe

> +	else
> +		BUILD_BUG_ON(1);
> +
>   	if (IS_ENABLED(CONFIG_PREEMPT))
>   		seq_buf_puts(&s, "PREEMPT ");
>   
> 

Re: [PATCH 2/2] powerpc: Show PAGE_SIZE in __die() output

[Christophe Leroy]

Le 08/01/2019 à 13:21, Christophe Leroy a écrit :
> 
> 
> Le 08/01/2019 à 13:05, Michael Ellerman a écrit :
>> The page size the kernel is built with is useful info when debugging a
>> crash, so add it to the output in __die().
>>
>> Result looks like eg:
>>
>>    kernel BUG at drivers/misc/lkdtm/bugs.c:63!
>>    Oops: Exception in kernel mode, sig: 5 [#1]
>>    LE PAGE_SIZE=64K SMP NR_CPUS=2048 NUMA pSeries
>>    Modules linked in: vmx_crypto kvm binfmt_misc ip_tables
>>
>> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
>> ---
>>   arch/powerpc/kernel/traps.c | 12 ++++++++++++
>>   1 file changed, 12 insertions(+)
>>
>> diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
>> index 431a86d3f772..fc972e4eee5f 100644
>> --- a/arch/powerpc/kernel/traps.c
>> +++ b/arch/powerpc/kernel/traps.c
>> @@ -268,6 +268,18 @@ static int __die(const char *str, struct pt_regs 
>> *regs, long err)
>>       else
>>           seq_buf_puts(&s, "BE ");
>> +    seq_buf_puts(&s, "PAGE_SIZE=");
>> +    if (IS_ENABLED(CONFIG_PPC_4K_PAGES))
>> +        seq_buf_puts(&s, "4K ");
>> +    else if (IS_ENABLED(CONFIG_PPC_16K_PAGES))
>> +        seq_buf_puts(&s, "16K ");
>> +    else if (IS_ENABLED(CONFIG_PPC_64K_PAGES))
>> +        seq_buf_puts(&s, "64K ");
>> +    else if (IS_ENABLED(CONFIG_PPC_256K_PAGES))
>> +        seq_buf_puts(&s, "256K ");
> 
> Can't we build all the above at once using PAGE_SHIFT ?
> 
> Something like (untested):
> 
> "%dK ", 1 << (PAGE_SHIFT - 10)

Or even simplier:

"%dK ", PAGE_SIZE / 1024

Christophe


> 
> Christophe
> 
>> +    else
>> +        BUILD_BUG_ON(1);
>> +
>>       if (IS_ENABLED(CONFIG_PREEMPT))
>>           seq_buf_puts(&s, "PREEMPT ");
>>

Re: [PATCH 2/2] powerpc: Show PAGE_SIZE in __die() output

[Michael Ellerman]

Christophe Leroy <christophe.leroy@c-s.fr> writes:
> Le 08/01/2019 à 13:21, Christophe Leroy a écrit :
>> Le 08/01/2019 à 13:05, Michael Ellerman a écrit :
>>> The page size the kernel is built with is useful info when debugging a
>>> crash, so add it to the output in __die().
>>>
>>> Result looks like eg:
>>>
>>>    kernel BUG at drivers/misc/lkdtm/bugs.c:63!
>>>    Oops: Exception in kernel mode, sig: 5 [#1]
>>>    LE PAGE_SIZE=64K SMP NR_CPUS=2048 NUMA pSeries
>>>    Modules linked in: vmx_crypto kvm binfmt_misc ip_tables
>>>
>>> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
>>> ---
>>>   arch/powerpc/kernel/traps.c | 12 ++++++++++++
>>>   1 file changed, 12 insertions(+)
>>>
>>> diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
>>> index 431a86d3f772..fc972e4eee5f 100644
>>> --- a/arch/powerpc/kernel/traps.c
>>> +++ b/arch/powerpc/kernel/traps.c
>>> @@ -268,6 +268,18 @@ static int __die(const char *str, struct pt_regs 
>>> *regs, long err)
>>>       else
>>>           seq_buf_puts(&s, "BE ");
>>> +    seq_buf_puts(&s, "PAGE_SIZE=");
>>> +    if (IS_ENABLED(CONFIG_PPC_4K_PAGES))
>>> +        seq_buf_puts(&s, "4K ");
>>> +    else if (IS_ENABLED(CONFIG_PPC_16K_PAGES))
>>> +        seq_buf_puts(&s, "16K ");
>>> +    else if (IS_ENABLED(CONFIG_PPC_64K_PAGES))
>>> +        seq_buf_puts(&s, "64K ");
>>> +    else if (IS_ENABLED(CONFIG_PPC_256K_PAGES))
>>> +        seq_buf_puts(&s, "256K ");
>> 
>> Can't we build all the above at once using PAGE_SHIFT ?
>> 
>> Something like (untested):
>> 
>> "%dK ", 1 << (PAGE_SHIFT - 10)
>
> Or even simplier:
>
> "%dK ", PAGE_SIZE / 1024

Yep, good point.

Clearly I have forgotten how to program over the break (if I ever knew).

cheers

Re: [PATCH 1/2] powerpc: Use seq_buf to avoid pr_cont() in __die()

[Michael Ellerman]

Christophe Leroy <christophe.leroy@c-s.fr> writes:
> Le 08/01/2019 à 13:04, Michael Ellerman a écrit :
>> Using pr_cont() risks having our output interleaved with other output
>> from other CPUs. Instead use a seq_buf to construct the line and then
>> print it as a whole.
>
> Why not simply doing a single printk() or similar on the same model as 
> X86 for instance ? 
> (https://elixir.bootlin.com/linux/v5.0-rc1/source/arch/x86/kernel/dumpstack.c#L368)

Yeah we could do it that way, though it can become a bit of a mess.

In this case I guess it's not *too* bad:

	printk("%s PAGE_SIZE=%luK%s%s%s%s%s %s\n",
	       IS_ENABLED(CONFIG_CPU_LITTLE_ENDIAN) ? "LE" : "BE",
	       PAGE_SIZE / 1024,
	       IS_ENABLED(CONFIG_PREEMPT) ? " PREEMPT" : "",
	       IS_ENABLED(CONFIG_SMP) ? " SMP" : "",
	       IS_ENABLED(CONFIG_SMP) ? (" NR_CPUS=" __stringify(NR_CPUS)) : "",
	       debug_pagealloc_enabled() ? " DEBUG_PAGEALLOC" : "",
	       IS_ENABLED(CONFIG_NUMA) ? " NUMA" : "",
	       ppc_md.name ? ppc_md.name : "");

And the generated code is obviously a lot smaller.

So yeah I'll go with that. Thanks for the review.

cheers