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Re: [PATCH] kasan: Respect /proc/sys/kernel/traceoff_on_warning

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  Re: [PATCH] kasan: Respect /proc/sys/kernel/traceoff_on_warning Peter Zijlstra <peterz@infradead.org> - 2017-01-25 15:30 +0100
    Re: [PATCH] kasan: Respect /proc/sys/kernel/traceoff_on_warning Alexander Potapenko <glider@google.com> - 2017-01-25 15:40 +0100
      Re: [PATCH] kasan: Respect /proc/sys/kernel/traceoff_on_warning Alexander Potapenko <glider@google.com> - 2017-01-25 15:40 +0100
      Re: [PATCH] kasan: Respect /proc/sys/kernel/traceoff_on_warning Peter Zijlstra <peterz@infradead.org> - 2017-01-25 15:40 +0100

#1566645 — Re: [PATCH] kasan: Respect /proc/sys/kernel/traceoff_on_warning

On Wed, Jan 25, 2017 at 03:25:24PM +0100, Peter Zijlstra wrote:
> 
> After much waiting I finally reproduced a KASAN issue, only to find my
> trace-buffer empty of useful information because it got spooled out :/
> 
> Make kasan_report honour the /proc/sys/kernel/traceoff_on_warning
> interface.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---

Seems to compile better when you add the required header files...

 mm/kasan/report.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index b82b3e2..3653ed1 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -24,6 +24,7 @@
 #include <linux/types.h>
 #include <linux/kasan.h>
 #include <linux/module.h>
+#include <linux/ftrace.h>
 
 #include <asm/sections.h>
 
@@ -300,6 +301,8 @@ void kasan_report(unsigned long addr, size_t size,
 	if (likely(!kasan_report_enabled()))
 		return;
 
+	disable_trace_on_warning();
+
 	info.access_addr = (void *)addr;
 	info.access_size = size;
 	info.is_write = is_write;

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#1566650

On Wed, Jan 25, 2017 at 3:28 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Wed, Jan 25, 2017 at 03:25:24PM +0100, Peter Zijlstra wrote:
>>
>> After much waiting I finally reproduced a KASAN issue, only to find my
>> trace-buffer empty of useful information because it got spooled out :/
>>
>> Make kasan_report honour the /proc/sys/kernel/traceoff_on_warning
>> interface.
>>
>> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
>> ---
>
> Seems to compile better when you add the required header files...
>
>  mm/kasan/report.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> index b82b3e2..3653ed1 100644
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -24,6 +24,7 @@
>  #include <linux/types.h>
>  #include <linux/kasan.h>
>  #include <linux/module.h>
> +#include <linux/ftrace.h>
>
>  #include <asm/sections.h>
>
> @@ -300,6 +301,8 @@ void kasan_report(unsigned long addr, size_t size,
>         if (likely(!kasan_report_enabled()))
>                 return;
>
> +       disable_trace_on_warning();
> +
Who is going to enable tracing back after we're done?
Note that KASAN errors are not fatal, and the first one may possibly
occur quite early.
>         info.access_addr = (void *)addr;
>         info.access_size = size;
>         info.is_write = is_write;



-- 
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Straße, 33
80636 München

Geschäftsführer: Matthew Scott Sucherman, Paul Terence Manicle
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg

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#1566652

On Wed, Jan 25, 2017 at 3:35 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Wed, Jan 25, 2017 at 03:32:11PM +0100, Alexander Potapenko wrote:
>
>> > @@ -300,6 +301,8 @@ void kasan_report(unsigned long addr, size_t size,
>> >         if (likely(!kasan_report_enabled()))
>> >                 return;
>> >
>> > +       disable_trace_on_warning();
>> > +
>> Who is going to enable tracing back after we're done?
>
> The user..
>
>> Note that KASAN errors are not fatal, and the first one may possibly
>> occur quite early.
>
> WARN*() isn't fatal either, and it does the same thing. Note that
> traceoff_on_warning is default disabled. You have to explicitly request
> this.
Ah, that makes sense. Sorry, I wasn't aware of that interface before.



-- 
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Straße, 33
80636 München

Geschäftsführer: Matthew Scott Sucherman, Paul Terence Manicle
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg

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#1566653

On Wed, Jan 25, 2017 at 03:32:11PM +0100, Alexander Potapenko wrote:

> > @@ -300,6 +301,8 @@ void kasan_report(unsigned long addr, size_t size,
> >         if (likely(!kasan_report_enabled()))
> >                 return;
> >
> > +       disable_trace_on_warning();
> > +
> Who is going to enable tracing back after we're done?

The user..

> Note that KASAN errors are not fatal, and the first one may possibly
> occur quite early.

WARN*() isn't fatal either, and it does the same thing. Note that
traceoff_on_warning is default disabled. You have to explicitly request
this.

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