[PATCH 1/2] arm64: Call __show_regs directly

[PATCH 1/2] arm64: Call __show_regs directly

[Kefeng Wang]

Call __show_regs directly in longjmp_break_handler() and
__do_user_fault(), it is to prepare for dump stack when
softlockup detected.

Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
---
 arch/arm64/kernel/probes/kprobes.c | 4 ++--
 arch/arm64/mm/fault.c              | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index c5c4594..d849d98 100644
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c
@@ -522,9 +522,9 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 		pr_err("current sp %lx does not match saved sp %lx\n",
 		       orig_sp, stack_addr);
 		pr_err("Saved registers for jprobe %p\n", jp);
-		show_regs(saved_regs);
+		__show_regs(saved_regs);
 		pr_err("Current registers\n");
-		show_regs(regs);
+		__show_regs(regs);
 		BUG();
 	}
 	unpause_graph_tracing();
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 37b95df..c3f2b10 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -250,7 +250,7 @@ static void __do_user_fault(struct task_struct *tsk, unsigned long addr,
 			tsk->comm, task_pid_nr(tsk), inf->name, sig,
 			addr, esr);
 		show_pte(tsk->mm, addr);
-		show_regs(regs);
+		__show_regs(regs);
 	}
 
 	tsk->thread.fault_address = addr;
-- 
1.7.12.4

[PATCH 2/2] arm64: Add dump_backtrace() in show_regs

[Kefeng Wang]

When the system trigger a softlockup(eg, infinite loop when
PREEMPT_NONE), it only shows regs without stack trace, which
makes it difficult to adress the issue.

Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
---
 arch/arm64/include/asm/stacktrace.h | 1 +
 arch/arm64/kernel/process.c         | 1 +
 arch/arm64/kernel/traps.c           | 2 +-
 3 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
index 801a16db..5b6eafc 100644
--- a/arch/arm64/include/asm/stacktrace.h
+++ b/arch/arm64/include/asm/stacktrace.h
@@ -30,5 +30,6 @@ struct stackframe {
 extern int unwind_frame(struct task_struct *tsk, struct stackframe *frame);
 extern void walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
 			    int (*fn)(struct stackframe *, void *), void *data);
+extern void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk);
 
 #endif	/* __ASM_STACKTRACE_H */
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index ae2a835..af1ea25 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -210,6 +210,7 @@ void __show_regs(struct pt_regs *regs)
 void show_regs(struct pt_regs * regs)
 {
 	__show_regs(regs);
+	dump_backtrace(regs, NULL);
 }
 
 static void tls_thread_flush(void)
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index d4d6ae0..368c3c8 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -140,7 +140,7 @@ static void dump_instr(const char *lvl, struct pt_regs *regs)
 	}
 }
 
-static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
+void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
 {
 	struct stackframe frame;
 	unsigned long irq_stack_ptr;
-- 
1.7.12.4

[PATCH 1/2] arm64: Call __show_regs directly

[Mark Rutland]

Hi,

I see these patches are effectively a v2 of [1].

Please cite prior patch series when posting updates. The context really
helps review.

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2017-March/494840.html

On Mon, May 08, 2017 at 09:56:54PM +0800, Kefeng Wang wrote:
> Call __show_regs directly in longjmp_break_handler() and
> __do_user_fault(), it is to prepare for dump stack when
> softlockup detected.
> 
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>

The above doesn't explain the problem clearly. How about:

  Generic code expects show_regs() to also dump the stack, but arm64's
  show_reg() does not do this. Some arm64 callers of show_regs() *only*
  want the registers dumped, without the stack.

  To enable generic code to work as expected, we need to make
  show_regs() dump the stack. Where we only want the registers dumped,
  we must use __show_regs().

  This patch updates code to use __show_regs() where only registers are
  desired. A subsequent patch will modify show_regs().

... with that:

Acked-by: Mark Rutland <mark.rutland@arm.com>

Thanks,
Mark.

> ---
>  arch/arm64/kernel/probes/kprobes.c | 4 ++--
>  arch/arm64/mm/fault.c              | 2 +-
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
> index c5c4594..d849d98 100644
> --- a/arch/arm64/kernel/probes/kprobes.c
> +++ b/arch/arm64/kernel/probes/kprobes.c
> @@ -522,9 +522,9 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
>  		pr_err("current sp %lx does not match saved sp %lx\n",
>  		       orig_sp, stack_addr);
>  		pr_err("Saved registers for jprobe %p\n", jp);
> -		show_regs(saved_regs);
> +		__show_regs(saved_regs);
>  		pr_err("Current registers\n");
> -		show_regs(regs);
> +		__show_regs(regs);
>  		BUG();
>  	}
>  	unpause_graph_tracing();
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index 37b95df..c3f2b10 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -250,7 +250,7 @@ static void __do_user_fault(struct task_struct *tsk, unsigned long addr,
>  			tsk->comm, task_pid_nr(tsk), inf->name, sig,
>  			addr, esr);
>  		show_pte(tsk->mm, addr);
> -		show_regs(regs);
> +		__show_regs(regs);
>  	}
>  
>  	tsk->thread.fault_address = addr;
> -- 
> 1.7.12.4
> 

[PATCH 2/2] arm64: Add dump_backtrace() in show_regs

[Mark Rutland]

On Mon, May 08, 2017 at 09:56:55PM +0800, Kefeng Wang wrote:
> When the system trigger a softlockup(eg, infinite loop when
> PREEMPT_NONE), it only shows regs without stack trace, which
> makes it difficult to adress the issue.

How about:

  Generic code expects show_regs() to dump the stack, but arm64's
  show_regs() does not. This makes it hard to debug softlockups and
  other issues that reesult in show_regs() being called.

  This patch updates arm64's show_regs() to dump the stack, as common
  code expects.

> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> ---
>  arch/arm64/include/asm/stacktrace.h | 1 +
>  arch/arm64/kernel/process.c         | 1 +
>  arch/arm64/kernel/traps.c           | 2 +-
>  3 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
> index 801a16db..5b6eafc 100644
> --- a/arch/arm64/include/asm/stacktrace.h
> +++ b/arch/arm64/include/asm/stacktrace.h
> @@ -30,5 +30,6 @@ struct stackframe {
>  extern int unwind_frame(struct task_struct *tsk, struct stackframe *frame);
>  extern void walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
>  			    int (*fn)(struct stackframe *, void *), void *data);
> +extern void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk);
>  
>  #endif	/* __ASM_STACKTRACE_H */
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index ae2a835..af1ea25 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -210,6 +210,7 @@ void __show_regs(struct pt_regs *regs)
>  void show_regs(struct pt_regs * regs)
>  {
>  	__show_regs(regs);
> +	dump_backtrace(regs, NULL);
>  }

I believe that as we pass the regs down, this should trigger the frame
skipping that we want, as I mentioned in reply to v1 [1].

So FWIW, with the commit message fixup:

Acked-by: Mark Rutland <mark.rutland@arm.com>

Thanks,
Mark.

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2017-March/496377.html

>  static void tls_thread_flush(void)
> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> index d4d6ae0..368c3c8 100644
> --- a/arch/arm64/kernel/traps.c
> +++ b/arch/arm64/kernel/traps.c
> @@ -140,7 +140,7 @@ static void dump_instr(const char *lvl, struct pt_regs *regs)
>  	}
>  }
>  
> -static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
> +void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
>  {
>  	struct stackframe frame;
>  	unsigned long irq_stack_ptr;
> -- 
> 1.7.12.4
> 

[PATCH 2/2] arm64: Add dump_backtrace() in show_regs

[Kefeng Wang]

On 2017/5/8 23:04, Mark Rutland wrote:
> On Mon, May 08, 2017 at 09:56:55PM +0800, Kefeng Wang wrote:
>> When the system trigger a softlockup(eg, infinite loop when
>> PREEMPT_NONE), it only shows regs without stack trace, which
>> makes it difficult to adress the issue.
> 
> How about:
> 
>   Generic code expects show_regs() to dump the stack, but arm64's
>   show_regs() does not. This makes it hard to debug softlockups and
>   other issues that reesult in show_regs() being called.
> 
>   This patch updates arm64's show_regs() to dump the stack, as common
>   code expects.
> 

Will update, thanks.

>> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
>> ---
>>  arch/arm64/include/asm/stacktrace.h | 1 +
>>  arch/arm64/kernel/process.c         | 1 +
>>  arch/arm64/kernel/traps.c           | 2 +-
>>  3 files changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
>> index 801a16db..5b6eafc 100644
>> --- a/arch/arm64/include/asm/stacktrace.h
>> +++ b/arch/arm64/include/asm/stacktrace.h
>> @@ -30,5 +30,6 @@ struct stackframe {
>>  extern int unwind_frame(struct task_struct *tsk, struct stackframe *frame);
>>  extern void walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
>>  			    int (*fn)(struct stackframe *, void *), void *data);
>> +extern void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk);
>>  
>>  #endif	/* __ASM_STACKTRACE_H */
>> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
>> index ae2a835..af1ea25 100644
>> --- a/arch/arm64/kernel/process.c
>> +++ b/arch/arm64/kernel/process.c
>> @@ -210,6 +210,7 @@ void __show_regs(struct pt_regs *regs)
>>  void show_regs(struct pt_regs * regs)
>>  {
>>  	__show_regs(regs);
>> +	dump_backtrace(regs, NULL);
>>  }
> 
> I believe that as we pass the regs down, this should trigger the frame
> skipping that we want, as I mentioned in reply to v1 [1].
> 
> So FWIW, with the commit message fixup:
> 
> Acked-by: Mark Rutland <mark.rutland@arm.com>

Thanks for your careful guidance, will update both.

Kefeng

> 
> Thanks,
> Mark.
> 
> [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2017-March/496377.html
> 
>>  static void tls_thread_flush(void)
>> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
>> index d4d6ae0..368c3c8 100644
>> --- a/arch/arm64/kernel/traps.c
>> +++ b/arch/arm64/kernel/traps.c
>> @@ -140,7 +140,7 @@ static void dump_instr(const char *lvl, struct pt_regs *regs)
>>  	}
>>  }
>>  
>> -static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
>> +void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
>>  {
>>  	struct stackframe frame;
>>  	unsigned long irq_stack_ptr;
>> -- 
>> 1.7.12.4
>>
> 
> .
> 

[PATCH v2 1/2] arm64: Call __show_regs directly

[Kefeng Wang]

Generic code expects show_regs() to also dump the stack, but arm64's
show_reg() does not do this. Some arm64 callers of show_regs() *only*
want the registers dumped, without the stack.

To enable generic code to work as expected, we need to make
show_regs() dump the stack. Where we only want the registers dumped,
we must use __show_regs().

This patch updates code to use __show_regs() where only registers are
desired. A subsequent patch will modify show_regs().

Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
---

v1->v2:
- Update the changelog according to Mark's kindly review, thanks Mark again.

Please see the background from link [1].

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2017-March/494840.html

 arch/arm64/kernel/probes/kprobes.c | 4 ++--
 arch/arm64/mm/fault.c              | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index c5c4594..d849d98 100644
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c
@@ -522,9 +522,9 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 		pr_err("current sp %lx does not match saved sp %lx\n",
 		       orig_sp, stack_addr);
 		pr_err("Saved registers for jprobe %p\n", jp);
-		show_regs(saved_regs);
+		__show_regs(saved_regs);
 		pr_err("Current registers\n");
-		show_regs(regs);
+		__show_regs(regs);
 		BUG();
 	}
 	unpause_graph_tracing();
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 37b95df..c3f2b10 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -250,7 +250,7 @@ static void __do_user_fault(struct task_struct *tsk, unsigned long addr,
 			tsk->comm, task_pid_nr(tsk), inf->name, sig,
 			addr, esr);
 		show_pte(tsk->mm, addr);
-		show_regs(regs);
+		__show_regs(regs);
 	}
 
 	tsk->thread.fault_address = addr;
-- 
1.7.12.4

[PATCH v2 2/2] arm64: Add dump_backtrace() in show_regs

[Kefeng Wang]

Generic code expects show_regs() to dump the stack, but arm64's
show_regs() does not. This makes it hard to debug softlockups and
other issues that result in show_regs() being called.

This patch updates arm64's show_regs() to dump the stack, as common
code expects.

Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
---
 arch/arm64/include/asm/stacktrace.h | 1 +
 arch/arm64/kernel/process.c         | 1 +
 arch/arm64/kernel/traps.c           | 2 +-
 3 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
index 801a16db..5b6eafc 100644
--- a/arch/arm64/include/asm/stacktrace.h
+++ b/arch/arm64/include/asm/stacktrace.h
@@ -30,5 +30,6 @@ struct stackframe {
 extern int unwind_frame(struct task_struct *tsk, struct stackframe *frame);
 extern void walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
 			    int (*fn)(struct stackframe *, void *), void *data);
+extern void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk);
 
 #endif	/* __ASM_STACKTRACE_H */
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index ae2a835..af1ea25 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -210,6 +210,7 @@ void __show_regs(struct pt_regs *regs)
 void show_regs(struct pt_regs * regs)
 {
 	__show_regs(regs);
+	dump_backtrace(regs, NULL);
 }
 
 static void tls_thread_flush(void)
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index d4d6ae0..368c3c8 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -140,7 +140,7 @@ static void dump_instr(const char *lvl, struct pt_regs *regs)
 	}
 }
 
-static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
+void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
 {
 	struct stackframe frame;
 	unsigned long irq_stack_ptr;
-- 
1.7.12.4

[PATCH v2 2/2] arm64: Add dump_backtrace() in show_regs

[Mark Rutland]

Hi,

On Tue, May 09, 2017 at 09:53:37AM +0800, Kefeng Wang wrote:
> Generic code expects show_regs() to dump the stack, but arm64's
> show_regs() does not. This makes it hard to debug softlockups and
> other issues that result in show_regs() being called.
> 
> This patch updates arm64's show_regs() to dump the stack, as common
> code expects.
> 
> Acked-by: Mark Rutland <mark.rutland@arm.com>
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> ---
>  arch/arm64/include/asm/stacktrace.h | 1 +
>  arch/arm64/kernel/process.c         | 1 +
>  arch/arm64/kernel/traps.c           | 2 +-
>  3 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
> index 801a16db..5b6eafc 100644
> --- a/arch/arm64/include/asm/stacktrace.h
> +++ b/arch/arm64/include/asm/stacktrace.h
> @@ -30,5 +30,6 @@ struct stackframe {
>  extern int unwind_frame(struct task_struct *tsk, struct stackframe *frame);
>  extern void walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
>  			    int (*fn)(struct stackframe *, void *), void *data);
> +extern void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk);
>  
>  #endif	/* __ASM_STACKTRACE_H */
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index ae2a835..af1ea25 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -210,6 +210,7 @@ void __show_regs(struct pt_regs *regs)
>  void show_regs(struct pt_regs * regs)
>  {
>  	__show_regs(regs);
> +	dump_backtrace(regs, NULL);
>  }
>  
>  static void tls_thread_flush(void)
> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> index d4d6ae0..368c3c8 100644
> --- a/arch/arm64/kernel/traps.c
> +++ b/arch/arm64/kernel/traps.c
> @@ -140,7 +140,7 @@ static void dump_instr(const char *lvl, struct pt_regs *regs)
>  	}
>  }
>  
> -static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
> +void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
>  {
>  	struct stackframe frame;
>  	unsigned long irq_stack_ptr;

I just realised that we'll need one additional fixup:

diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 0805b44..f452fcc 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -728,8 +728,6 @@ static int bug_handler(struct pt_regs *regs, unsigned int esr)
                break;
 
        case BUG_TRAP_TYPE_WARN:
-               /* Ideally, report_bug() should backtrace for us... but no. */
-               dump_backtrace(regs, NULL);
                break;
 
        default:

... since report_bug() will call show_regs(), and dump the stack itself
now.

With that change, these patches will also fix *_ONCE() traps spewing
backtraces every time they're invoked, which was a side-effect of
commit:

  19d436268dde9538 ("debug: Add _ONCE() logic to report_bug()")

Would you mind folding that into a v3?

Thanks,
Mark.

[PATCH v2 2/2] arm64: Add dump_backtrace() in show_regs

[Will Deacon]

On Wed, May 24, 2017 at 11:09:49AM +0100, Mark Rutland wrote:
> On Tue, May 09, 2017 at 09:53:37AM +0800, Kefeng Wang wrote:
> > Generic code expects show_regs() to dump the stack, but arm64's
> > show_regs() does not. This makes it hard to debug softlockups and
> > other issues that result in show_regs() being called.
> > 
> > This patch updates arm64's show_regs() to dump the stack, as common
> > code expects.
> > 
> > Acked-by: Mark Rutland <mark.rutland@arm.com>
> > Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>

[...]

> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> index 0805b44..f452fcc 100644
> --- a/arch/arm64/kernel/traps.c
> +++ b/arch/arm64/kernel/traps.c
> @@ -728,8 +728,6 @@ static int bug_handler(struct pt_regs *regs, unsigned int esr)
>                 break;
>  
>         case BUG_TRAP_TYPE_WARN:
> -               /* Ideally, report_bug() should backtrace for us... but no. */
> -               dump_backtrace(regs, NULL);
>                 break;
>  
>         default:
> 
> ... since report_bug() will call show_regs(), and dump the stack itself
> now.
> 
> With that change, these patches will also fix *_ONCE() traps spewing
> backtraces every time they're invoked, which was a side-effect of
> commit:
> 
>   19d436268dde9538 ("debug: Add _ONCE() logic to report_bug()")
> 
> Would you mind folding that into a v3?

I've queued this locally, so I can just fold that in too. No need to repost.

I'll push what I have at -rc3.

Cheers,

Will