[v2] ARC: prevent showing irrelevant exception info in signal message

We process signals in the end of syscall/exception handler.
It the signal is fatal we print register's content using
show_regs function. show_regs() also prints information about
last exception happened.

In case of multicore system we can catch the situation when we
will print wrong information about exception. See the example:

Hi Vineet,

any chance you could look at this?
Otherwise we will both forget what it is all about :)

On Tue, 2018-08-07 at 16:59 +0300, Eugeniy Paltsev wrote:
> We process signals in the end of syscall/exception handler.
> It the signal is fatal we print register's content using
> show_regs function. show_regs() also prints information about
> last exception happened.
> 
> In case of multicore system we can catch the situation when we
> will print wrong information about exception. See the example:
> ______________________________
> CPU-0: started to handle page fault
> CPU-1: sent signal to process, which is executed on CPU-0
> CPU-0: ended page fault handle. Started to process signal before
>        returnig to userspace. Process signal, which is send from
>        CPU-0. As th signal is fatal we call show_regs().
>        show_regs() will show information about last exception
>        which is *page fault* (instead of "trap" which is used for
>        signals and happened on CPU-0)
> 
> So we will get message like this:
>    # ./waitpid02
>   potentially unexpected fatal signal 8.
>   Path: /home/waitpid02
>   CPU: 0 PID: 100 Comm: waitpid02 Not tainted 4.10.0-rc4 #2
>   task: 9f11c200 task.stack: 9f3ae000
> 
>   [ECR   ]: 0x00050200 => Invalid Write @ 0x00000000 by insn @ 0x000123ec
>   [EFA   ]: 0x00000000
>   [BLINK ]: 0x123ea
>   [ERET  ]: 0x123ec
>     @off 0x123ec in [/home/waitpid02]
>     VMA: 0x00010000 to 0x00016000
>   [STAT32]: 0x80080882 : IE U
>   BTA: 0x000123ea  SP: 0x5ffd3db0  FP: 0x00000000
>   LPS: 0x20031684 LPE: 0x2003169a LPC: 0x00000006
>   [-----other-info-----]
> 
> This message is confusing because it show information about page fault
> ( [ECR   ]: 0x00050200 => Invalid Write ) which is absolutely irrelevant
> to signal.
> 
> This situation was reproduced with waitpid02 LTP test.
> _____________________________
> 
> So remove printing information about exceptions from show_regs()
> to avoid confusing messages. Print information about exceptions
> only in required places instead of show_regs()
> 
> Now we don't print information about exceptions if signal is simply
> send by another userspace app. So in case of waitpid02 we will print
> next message:
> _____________________________
>    # ./waitpid02
>   potentially unexpected fatal signal 8.
>   Path: /root/waitpid02
>   CPU: 2 PID: 105 Comm: waitpid02 Not tainted 4.18.0-rc8-00002-gde0f6d6aeb53-dirty #17
>   [ECR   ]: 0x00050100
>   [EFA   ]: 0x00000000
>   [BLINK ]: 0x20001486
>   [-----other-info-----]
> _____________________________
> 
> This patch fix
> STAR 9001146055: waitpid02: Invalid Write @ 0x00000000 by insn @ 0x000123ec
> 
> NOTE:
> To be more clear I give examples of different faults (signal-based,
> userspace/kernelspace exception-based) with different values of
> "/proc/sys/kernel/print-fatal-signals" option.
> 
> 0) NULL pointer access from user space, print-fatal-signals == 1:
> ------------>8---------------
>  # ./arc_hell
> Exception: arc_hell[103]: at 0x2003a35c [off 0x2e35c in /lib/libuClibc-1.0.18.so, VMA: 2000c000:20072000]
>   ECR: 0x00050100 => Invalid Read @ 0x00000000 by insn @ 0x2003a35c
> potentially unexpected fatal signal 11.
> Path: /root/arc_hell
> CPU: 1 PID: 103 Comm: arc_hell Not tainted 4.18.0-rc8-00002-gde0f6d6aeb53-dirty #17
> [ECR   ]: 0x00050100
> [EFA   ]: 0x00000000
> [BLINK ]: 0x20039ef8
> [ERET  ]: 0x2003a35c
> [STAT32]: 0x80080882 : IE U
> BTA: 0x2003a358  SP: 0x5fa27dc4  FP: 0x5fa27de8
> LPS: 0x2003a628 LPE: 0x2003a62c LPC: 0x00000000
> r00: 0x00000000 r01: 0x200740b0 r02: 0x00000001
> r03: 0x00000007 r04: 0x80808080 r05: 0x2f2f2f2f
> r06: 0x7c7a2f43 r07: 0x00000000 r08: 0x1a131100
> r09: 0x2008b1e0 r10: 0x20003a5c r11: 0x20004038
> r12: 0x20039ef8 r13: 0x200740b0 r14: 0x00000000
> r15: 0x200740b0 r16: 0x00000000 r17: 0x0007d468
> r18: 0x0009313a r19: 0x00000000 r20: 0x0009c22c
> r21: 0x0009c23c r22: 0x0009ab64 r23: 0x00000000
> r24: 0x0009dfc5 r25: 0x20004b70
> 
> Segmentation fault
> ------------>8---------------
> 
> 1) NULL pointer access from user space, print-fatal-signals == 0:
> ------------>8---------------
>  # ./arc_hell
> Exception: arc_hell[107]: at 0x2003a35c [off 0x2e35c in /lib/libuClibc-1.0.18.so, VMA: 2000c000:20072000]
>   ECR: 0x00050100 => Invalid Read @ 0x00000000 by insn @ 0x2003a35c
> Segmentation fault
> ------------>8---------------
> 
> 2) Process killed by signal (waitpid02 test), print-fatal-signals == 1:
> ------------>8---------------
>  # ./waitpid02
> potentially unexpected fatal signal 8.
> Path: /root/waitpid02
> CPU: 2 PID: 105 Comm: waitpid02 Not tainted 4.18.0-rc8-00002-gde0f6d6aeb53-dirty #17
> [ECR   ]: 0x00050100
> [EFA   ]: 0x00000000
> [BLINK ]: 0x20001486
> [ERET  ]: 0x2000146c
> [STAT32]: 0x80080082 : IE U
> BTA: 0x20000fc4  SP: 0x5fa21d64  FP: 0x00000000
> LPS: 0x200524a0 LPE: 0x200524b6 LPC: 0x00000006
> r00: 0x2000c0dc r01: 0x00000018 r02: 0x0001159a
> r03: 0x00000001 r04: 0x00000000 r05: 0x00000045
> r06: 0x0000004e r07: 0x01010101 r08: 0x000000dc
> r09: 0x200a31e0 r10: 0x20003a5c r11: 0x20004038
> r12: 0x20001486 r13: 0x20004174 r14: 0x07ca2bc0
> r15: 0x20004078 r16: 0x00000000 r17: 0x20004038
> r18: 0x00000001 r19: 0x00000000 r20: 0x0001159a
> r21: 0x00000001 r22: 0x00000000 r23: 0x00000004
> r24: 0x2000d1fc r25: 0x20004cd0
> ------------>8---------------
> 
> 3) Process killed by signal (waitpid02 test), print-fatal-signals == 0:
> ------------>8---------------
>  # ./waitpid02
> ------------>8---------------
> 
> 4) NULL pointer access from kernel space, regardless print-fatal-signals
> value:
> ------------>8---------------
> Oops
> Exception: at stmmac_dvr_probe+0x40/0x7e0:
>   ECR: 0x00050200 => Invalid Write @ 0x00000000 by insn @ 0x90575254
> Path: (null)
> CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.18.0-rc8-00002-gde0f6d6aeb53-dirty #11
> [EFA   ]: 0x00000000
> [BLINK ]: stmmac_dvr_probe+0x2a/0x7e0
> [ERET  ]: stmmac_dvr_probe+0x40/0x7e0
> [STAT32]: 0x80080402 : IE K
> BTA: 0x9057523e  SP: 0xbf02be40  FP: 0x00000000
> LPS: 0x9073dbcc LPE: 0x9073dbe0 LPC: 0x00000000
> r00: 0xbf1f0000 r01: 0x00000000 r02: 0x00000008
> r03: 0x00000000 r04: 0x00000064 r05: 0x00000000
> r06: 0x00000003 r07: 0x00000004 r08: 0x01010101
> r09: 0x00000031 r10: 0xbf1f0006 r11: 0x00000000
> r12: 0x9057523e
> 
> Stack Trace:
>   stmmac_dvr_probe+0x40/0x7e0
>   dwmac_generic_probe+0x50/0xbc
>   platform_drv_probe+0x26/0x5c
>   really_probe+0x3b0/0x464
>   __driver_attach+0xd4/0xd8
>   bus_for_each_dev+0x3a/0x70
>   bus_add_driver+0x12a/0x18c
>   driver_register+0x56/0xe8
>   do_one_initcall+0x2e/0x118
>   kernel_init_freeable+0x102/0x194
> ------------>8---------------
> 
> Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
> ---
> 
> NOTE:
>   This patch has prerequisites:
>   https://www.mail-archive.com/linux-snps-arc@lists.infradead.org/msg03938.html
>   https://www.mail-archive.com/linux-snps-arc@lists.infradead.org/msg03937.html
> 
> Changes v1->v2:
>  * Change format of message about exception.
> 
>  arch/arc/include/asm/bug.h     |  1 +
>  arch/arc/kernel/traps.c        |  1 +
>  arch/arc/kernel/troubleshoot.c | 51 +++++++++++++++++++++++++++++++++---------
>  arch/arc/mm/fault.c            |  2 ++
>  4 files changed, 44 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/arc/include/asm/bug.h b/arch/arc/include/asm/bug.h
> index 21ec82466d62..b68f7f82f2d8 100644
> --- a/arch/arc/include/asm/bug.h
> +++ b/arch/arc/include/asm/bug.h
> @@ -16,6 +16,7 @@
>  struct task_struct;
>  
>  void show_regs(struct pt_regs *regs);
> +void show_exception_mesg(struct pt_regs *regs);
>  void show_stacktrace(struct task_struct *tsk, struct pt_regs *regs);
>  void show_kernel_fault_diag(const char *str, struct pt_regs *regs,
>  			    unsigned long address);
> diff --git a/arch/arc/kernel/traps.c b/arch/arc/kernel/traps.c
> index b123558bf0bb..5d83b2fe5f12 100644
> --- a/arch/arc/kernel/traps.c
> +++ b/arch/arc/kernel/traps.c
> @@ -50,6 +50,7 @@ unhandled_exception(const char *str, struct pt_regs *regs, siginfo_t *info)
>  		tsk->thread.fault_address = (__force unsigned int)info->si_addr;
>  
>  		force_sig_info(info->si_signo, info, tsk);
> +		show_exception_mesg(regs);
>  
>  	} else {
>  		/* If not due to copy_(to|from)_user, we are doomed */
> diff --git a/arch/arc/kernel/troubleshoot.c b/arch/arc/kernel/troubleshoot.c
> index e8d9fb452346..fdfba1942a06 100644
> --- a/arch/arc/kernel/troubleshoot.c
> +++ b/arch/arc/kernel/troubleshoot.c
> @@ -101,13 +101,13 @@ static void show_faulting_vma(unsigned long address, char *buf)
>  			if (IS_ERR(nm))
>  				nm = "?";
>  		}
> -		pr_info("    @off 0x%lx in [%s]\n"
> -			"    VMA: 0x%08lx to 0x%08lx\n",
> +
> +		pr_cont("[off 0x%lx in %s, VMA: %08lx:%08lx] ",
>  			vma->vm_start < TASK_UNMAPPED_BASE ?
>  				address : address - vma->vm_start,
>  			nm, vma->vm_start, vma->vm_end);
>  	} else
> -		pr_info("    @No matching VMA found\n");
> +		pr_cont("[No matching VMA found] ");
>  
>  	up_read(&active_mm->mmap_sem);
>  }
> @@ -117,7 +117,7 @@ static void show_ecr_verbose(struct pt_regs *regs)
>  	unsigned int vec, cause_code;
>  	unsigned long address;
>  
> -	pr_info("\n[ECR   ]: 0x%08lx => ", regs->event);
> +	pr_cont("\n  ECR: 0x%08lx => ", regs->event);
>  
>  	/* For Data fault, this is data address not instruction addr */
>  	address = current->thread.fault_address;
> @@ -165,10 +165,42 @@ static void show_ecr_verbose(struct pt_regs *regs)
>  	}
>  }
>  
> +static inline void show_exception_mesg_u(struct pt_regs *regs)
> +{
> +	struct task_struct *tsk = current;
> +	char *buf;
> +
> +	pr_info("Exception: %s[%d]: at %pS ",
> +		tsk->comm, task_pid_nr(tsk), (void *)regs->ret);
> +
> +	buf = (char *)__get_free_page(GFP_NOWAIT);
> +	if (buf) {
> +		show_faulting_vma(regs->ret, buf);
> +		free_page((unsigned long)buf);
> +	}
> +
> +	show_ecr_verbose(regs);
> +}
> +
> +static inline void show_exception_mesg_k(struct pt_regs *regs)
> +{
> +	pr_info("Exception: at %pS:", (void *)regs->ret);
> +
> +	show_ecr_verbose(regs);
> +}
> +
>  /************************************************************************
>   *  API called by rest of kernel
>   ***********************************************************************/
>  
> +void show_exception_mesg(struct pt_regs *regs)
> +{
> +	if (user_mode(regs))
> +		show_exception_mesg_u(regs);
> +	else
> +		show_exception_mesg_k(regs);
> +}
> +
>  void show_regs(struct pt_regs *regs)
>  {
>  	struct task_struct *tsk = current;
> @@ -182,15 +214,10 @@ void show_regs(struct pt_regs *regs)
>  	print_task_path_n_nm(tsk, buf);
>  	show_regs_print_info(KERN_INFO);
>  
> -	show_ecr_verbose(regs);
> -
> -	pr_info("[EFA   ]: 0x%08lx\n[BLINK ]: %pS\n[ERET  ]: %pS\n",
> -		current->thread.fault_address,
> +	pr_info("[ECR   ]: 0x%08lx\n[EFA   ]: 0x%08lx\n[BLINK ]: %pS\n[ERET  ]: %pS\n",
> +		regs->event, current->thread.fault_address,
>  		(void *)regs->blink, (void *)regs->ret);
>  
> -	if (user_mode(regs))
> -		show_faulting_vma(regs->ret, buf); /* faulting code, not data */
> -
>  	pr_info("[STAT32]: 0x%08lx", regs->status32);
>  
>  #define STS_BIT(r, bit)	r->status32 & STATUS_##bit##_MASK ? #bit" " : ""
> @@ -233,6 +260,8 @@ void show_kernel_fault_diag(const char *str, struct pt_regs *regs,
>  	/* Show fault description */
>  	pr_info("\n%s\n", str);
>  
> +	show_exception_mesg(regs);
> +
>  	/* Caller and Callee regs */
>  	show_regs(regs);
>  
> diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c
> index b884bbd6f354..d9c6958a1702 100644
> --- a/arch/arc/mm/fault.c
> +++ b/arch/arc/mm/fault.c
> @@ -202,6 +202,7 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
>  		/* info.si_code has been set above */
>  		info.si_addr = (void __user *)address;
>  		force_sig_info(SIGSEGV, &info, tsk);
> +		show_exception_mesg(regs);
>  		return;
>  	}
>  
> @@ -241,4 +242,5 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
>  	info.si_code = BUS_ADRERR;
>  	info.si_addr = (void __user *)address;
>  	force_sig_info(SIGBUS, &info, tsk);
> +	show_exception_mesg(regs);
>  }

On 10/01/2018 09:50 AM, Eugeniy Paltsev wrote:
> Hi Vineet,
>
> any chance you could look at this?
> Otherwise we will both forget what it is all about :)

I was busy with non Linux stuff for quite some time - hopefully that should be
wrapped up and I can get back to tending you ;-)

-Vineet

>
> On Tue, 2018-08-07 at 16:59 +0300, Eugeniy Paltsev wrote:
>> We process signals in the end of syscall/exception handler.
>> It the signal is fatal we print register's content using
>> show_regs function. show_regs() also prints information about
>> last exception happened.
>>
>> In case of multicore system we can catch the situation when we
>> will print wrong information about exception. See the example:
>> ______________________________
>> CPU-0: started to handle page fault
>> CPU-1: sent signal to process, which is executed on CPU-0
>> CPU-0: ended page fault handle. Started to process signal before
>>        returnig to userspace. Process signal, which is send from
>>        CPU-0. As th signal is fatal we call show_regs().
>>        show_regs() will show information about last exception
>>        which is *page fault* (instead of "trap" which is used for
>>        signals and happened on CPU-0)
>>
>> So we will get message like this:
>>    # ./waitpid02
>>   potentially unexpected fatal signal 8.
>>   Path: /home/waitpid02
>>   CPU: 0 PID: 100 Comm: waitpid02 Not tainted 4.10.0-rc4 #2
>>   task: 9f11c200 task.stack: 9f3ae000
>>
>>   [ECR   ]: 0x00050200 => Invalid Write @ 0x00000000 by insn @ 0x000123ec
>>   [EFA   ]: 0x00000000
>>   [BLINK ]: 0x123ea
>>   [ERET  ]: 0x123ec
>>     @off 0x123ec in [/home/waitpid02]
>>     VMA: 0x00010000 to 0x00016000
>>   [STAT32]: 0x80080882 : IE U
>>   BTA: 0x000123ea  SP: 0x5ffd3db0  FP: 0x00000000
>>   LPS: 0x20031684 LPE: 0x2003169a LPC: 0x00000006
>>   [-----other-info-----]
>>
>> This message is confusing because it show information about page fault
>> ( [ECR   ]: 0x00050200 => Invalid Write ) which is absolutely irrelevant
>> to signal.
>>
>> This situation was reproduced with waitpid02 LTP test.
>> _____________________________
>>
>> So remove printing information about exceptions from show_regs()
>> to avoid confusing messages. Print information about exceptions
>> only in required places instead of show_regs()
>>
>> Now we don't print information about exceptions if signal is simply
>> send by another userspace app. So in case of waitpid02 we will print
>> next message:
>> _____________________________
>>    # ./waitpid02
>>   potentially unexpected fatal signal 8.
>>   Path: /root/waitpid02
>>   CPU: 2 PID: 105 Comm: waitpid02 Not tainted 4.18.0-rc8-00002-gde0f6d6aeb53-dirty #17
>>   [ECR   ]: 0x00050100
>>   [EFA   ]: 0x00000000
>>   [BLINK ]: 0x20001486
>>   [-----other-info-----]
>> _____________________________
>>
>> This patch fix
>> STAR 9001146055: waitpid02: Invalid Write @ 0x00000000 by insn @ 0x000123ec
>>
>> NOTE:
>> To be more clear I give examples of different faults (signal-based,
>> userspace/kernelspace exception-based) with different values of
>> "/proc/sys/kernel/print-fatal-signals" option.
>>
>> 0) NULL pointer access from user space, print-fatal-signals == 1:
>> ------------>8---------------
>>  # ./arc_hell
>> Exception: arc_hell[103]: at 0x2003a35c [off 0x2e35c in /lib/libuClibc-1.0.18.so, VMA: 2000c000:20072000]
>>   ECR: 0x00050100 => Invalid Read @ 0x00000000 by insn @ 0x2003a35c
>> potentially unexpected fatal signal 11.
>> Path: /root/arc_hell
>> CPU: 1 PID: 103 Comm: arc_hell Not tainted 4.18.0-rc8-00002-gde0f6d6aeb53-dirty #17
>> [ECR   ]: 0x00050100
>> [EFA   ]: 0x00000000
>> [BLINK ]: 0x20039ef8
>> [ERET  ]: 0x2003a35c
>> [STAT32]: 0x80080882 : IE U
>> BTA: 0x2003a358  SP: 0x5fa27dc4  FP: 0x5fa27de8
>> LPS: 0x2003a628 LPE: 0x2003a62c LPC: 0x00000000
>> r00: 0x00000000 r01: 0x200740b0 r02: 0x00000001
>> r03: 0x00000007 r04: 0x80808080 r05: 0x2f2f2f2f
>> r06: 0x7c7a2f43 r07: 0x00000000 r08: 0x1a131100
>> r09: 0x2008b1e0 r10: 0x20003a5c r11: 0x20004038
>> r12: 0x20039ef8 r13: 0x200740b0 r14: 0x00000000
>> r15: 0x200740b0 r16: 0x00000000 r17: 0x0007d468
>> r18: 0x0009313a r19: 0x00000000 r20: 0x0009c22c
>> r21: 0x0009c23c r22: 0x0009ab64 r23: 0x00000000
>> r24: 0x0009dfc5 r25: 0x20004b70
>>
>> Segmentation fault
>> ------------>8---------------
>>
>> 1) NULL pointer access from user space, print-fatal-signals == 0:
>> ------------>8---------------
>>  # ./arc_hell
>> Exception: arc_hell[107]: at 0x2003a35c [off 0x2e35c in /lib/libuClibc-1.0.18.so, VMA: 2000c000:20072000]
>>   ECR: 0x00050100 => Invalid Read @ 0x00000000 by insn @ 0x2003a35c
>> Segmentation fault
>> ------------>8---------------
>>
>> 2) Process killed by signal (waitpid02 test), print-fatal-signals == 1:
>> ------------>8---------------
>>  # ./waitpid02
>> potentially unexpected fatal signal 8.
>> Path: /root/waitpid02
>> CPU: 2 PID: 105 Comm: waitpid02 Not tainted 4.18.0-rc8-00002-gde0f6d6aeb53-dirty #17
>> [ECR   ]: 0x00050100
>> [EFA   ]: 0x00000000
>> [BLINK ]: 0x20001486
>> [ERET  ]: 0x2000146c
>> [STAT32]: 0x80080082 : IE U
>> BTA: 0x20000fc4  SP: 0x5fa21d64  FP: 0x00000000
>> LPS: 0x200524a0 LPE: 0x200524b6 LPC: 0x00000006
>> r00: 0x2000c0dc r01: 0x00000018 r02: 0x0001159a
>> r03: 0x00000001 r04: 0x00000000 r05: 0x00000045
>> r06: 0x0000004e r07: 0x01010101 r08: 0x000000dc
>> r09: 0x200a31e0 r10: 0x20003a5c r11: 0x20004038
>> r12: 0x20001486 r13: 0x20004174 r14: 0x07ca2bc0
>> r15: 0x20004078 r16: 0x00000000 r17: 0x20004038
>> r18: 0x00000001 r19: 0x00000000 r20: 0x0001159a
>> r21: 0x00000001 r22: 0x00000000 r23: 0x00000004
>> r24: 0x2000d1fc r25: 0x20004cd0
>> ------------>8---------------
>>
>> 3) Process killed by signal (waitpid02 test), print-fatal-signals == 0:
>> ------------>8---------------
>>  # ./waitpid02
>> ------------>8---------------
>>
>> 4) NULL pointer access from kernel space, regardless print-fatal-signals
>> value:
>> ------------>8---------------
>> Oops
>> Exception: at stmmac_dvr_probe+0x40/0x7e0:
>>   ECR: 0x00050200 => Invalid Write @ 0x00000000 by insn @ 0x90575254
>> Path: (null)
>> CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.18.0-rc8-00002-gde0f6d6aeb53-dirty #11
>> [EFA   ]: 0x00000000
>> [BLINK ]: stmmac_dvr_probe+0x2a/0x7e0
>> [ERET  ]: stmmac_dvr_probe+0x40/0x7e0
>> [STAT32]: 0x80080402 : IE K
>> BTA: 0x9057523e  SP: 0xbf02be40  FP: 0x00000000
>> LPS: 0x9073dbcc LPE: 0x9073dbe0 LPC: 0x00000000
>> r00: 0xbf1f0000 r01: 0x00000000 r02: 0x00000008
>> r03: 0x00000000 r04: 0x00000064 r05: 0x00000000
>> r06: 0x00000003 r07: 0x00000004 r08: 0x01010101
>> r09: 0x00000031 r10: 0xbf1f0006 r11: 0x00000000
>> r12: 0x9057523e
>>
>> Stack Trace:
>>   stmmac_dvr_probe+0x40/0x7e0
>>   dwmac_generic_probe+0x50/0xbc
>>   platform_drv_probe+0x26/0x5c
>>   really_probe+0x3b0/0x464
>>   __driver_attach+0xd4/0xd8
>>   bus_for_each_dev+0x3a/0x70
>>   bus_add_driver+0x12a/0x18c
>>   driver_register+0x56/0xe8
>>   do_one_initcall+0x2e/0x118
>>   kernel_init_freeable+0x102/0x194
>> ------------>8---------------
>>
>> Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
>> ---
>>
>> NOTE:
>>   This patch has prerequisites:
>>   https://www.mail-archive.com/linux-snps-arc@lists.infradead.org/msg03938.html
>>   https://www.mail-archive.com/linux-snps-arc@lists.infradead.org/msg03937.html
>>
>> Changes v1->v2:
>>  * Change format of message about exception.
>>
>>  arch/arc/include/asm/bug.h     |  1 +
>>  arch/arc/kernel/traps.c        |  1 +
>>  arch/arc/kernel/troubleshoot.c | 51 +++++++++++++++++++++++++++++++++---------
>>  arch/arc/mm/fault.c            |  2 ++
>>  4 files changed, 44 insertions(+), 11 deletions(-)
>>
>> diff --git a/arch/arc/include/asm/bug.h b/arch/arc/include/asm/bug.h
>> index 21ec82466d62..b68f7f82f2d8 100644
>> --- a/arch/arc/include/asm/bug.h
>> +++ b/arch/arc/include/asm/bug.h
>> @@ -16,6 +16,7 @@
>>  struct task_struct;
>>  
>>  void show_regs(struct pt_regs *regs);
>> +void show_exception_mesg(struct pt_regs *regs);
>>  void show_stacktrace(struct task_struct *tsk, struct pt_regs *regs);
>>  void show_kernel_fault_diag(const char *str, struct pt_regs *regs,
>>  			    unsigned long address);
>> diff --git a/arch/arc/kernel/traps.c b/arch/arc/kernel/traps.c
>> index b123558bf0bb..5d83b2fe5f12 100644
>> --- a/arch/arc/kernel/traps.c
>> +++ b/arch/arc/kernel/traps.c
>> @@ -50,6 +50,7 @@ unhandled_exception(const char *str, struct pt_regs *regs, siginfo_t *info)
>>  		tsk->thread.fault_address = (__force unsigned int)info->si_addr;
>>  
>>  		force_sig_info(info->si_signo, info, tsk);
>> +		show_exception_mesg(regs);
>>  
>>  	} else {
>>  		/* If not due to copy_(to|from)_user, we are doomed */
>> diff --git a/arch/arc/kernel/troubleshoot.c b/arch/arc/kernel/troubleshoot.c
>> index e8d9fb452346..fdfba1942a06 100644
>> --- a/arch/arc/kernel/troubleshoot.c
>> +++ b/arch/arc/kernel/troubleshoot.c
>> @@ -101,13 +101,13 @@ static void show_faulting_vma(unsigned long address, char *buf)
>>  			if (IS_ERR(nm))
>>  				nm = "?";
>>  		}
>> -		pr_info("    @off 0x%lx in [%s]\n"
>> -			"    VMA: 0x%08lx to 0x%08lx\n",
>> +
>> +		pr_cont("[off 0x%lx in %s, VMA: %08lx:%08lx] ",
>>  			vma->vm_start < TASK_UNMAPPED_BASE ?
>>  				address : address - vma->vm_start,
>>  			nm, vma->vm_start, vma->vm_end);
>>  	} else
>> -		pr_info("    @No matching VMA found\n");
>> +		pr_cont("[No matching VMA found] ");
>>  
>>  	up_read(&active_mm->mmap_sem);
>>  }
>> @@ -117,7 +117,7 @@ static void show_ecr_verbose(struct pt_regs *regs)
>>  	unsigned int vec, cause_code;
>>  	unsigned long address;
>>  
>> -	pr_info("\n[ECR   ]: 0x%08lx => ", regs->event);
>> +	pr_cont("\n  ECR: 0x%08lx => ", regs->event);
>>  
>>  	/* For Data fault, this is data address not instruction addr */
>>  	address = current->thread.fault_address;
>> @@ -165,10 +165,42 @@ static void show_ecr_verbose(struct pt_regs *regs)
>>  	}
>>  }
>>  
>> +static inline void show_exception_mesg_u(struct pt_regs *regs)
>> +{
>> +	struct task_struct *tsk = current;
>> +	char *buf;
>> +
>> +	pr_info("Exception: %s[%d]: at %pS ",
>> +		tsk->comm, task_pid_nr(tsk), (void *)regs->ret);
>> +
>> +	buf = (char *)__get_free_page(GFP_NOWAIT);
>> +	if (buf) {
>> +		show_faulting_vma(regs->ret, buf);
>> +		free_page((unsigned long)buf);
>> +	}
>> +
>> +	show_ecr_verbose(regs);
>> +}
>> +
>> +static inline void show_exception_mesg_k(struct pt_regs *regs)
>> +{
>> +	pr_info("Exception: at %pS:", (void *)regs->ret);
>> +
>> +	show_ecr_verbose(regs);
>> +}
>> +
>>  /************************************************************************
>>   *  API called by rest of kernel
>>   ***********************************************************************/
>>  
>> +void show_exception_mesg(struct pt_regs *regs)
>> +{
>> +	if (user_mode(regs))
>> +		show_exception_mesg_u(regs);
>> +	else
>> +		show_exception_mesg_k(regs);
>> +}
>> +
>>  void show_regs(struct pt_regs *regs)
>>  {
>>  	struct task_struct *tsk = current;
>> @@ -182,15 +214,10 @@ void show_regs(struct pt_regs *regs)
>>  	print_task_path_n_nm(tsk, buf);
>>  	show_regs_print_info(KERN_INFO);
>>  
>> -	show_ecr_verbose(regs);
>> -
>> -	pr_info("[EFA   ]: 0x%08lx\n[BLINK ]: %pS\n[ERET  ]: %pS\n",
>> -		current->thread.fault_address,
>> +	pr_info("[ECR   ]: 0x%08lx\n[EFA   ]: 0x%08lx\n[BLINK ]: %pS\n[ERET  ]: %pS\n",
>> +		regs->event, current->thread.fault_address,
>>  		(void *)regs->blink, (void *)regs->ret);
>>  
>> -	if (user_mode(regs))
>> -		show_faulting_vma(regs->ret, buf); /* faulting code, not data */
>> -
>>  	pr_info("[STAT32]: 0x%08lx", regs->status32);
>>  
>>  #define STS_BIT(r, bit)	r->status32 & STATUS_##bit##_MASK ? #bit" " : ""
>> @@ -233,6 +260,8 @@ void show_kernel_fault_diag(const char *str, struct pt_regs *regs,
>>  	/* Show fault description */
>>  	pr_info("\n%s\n", str);
>>  
>> +	show_exception_mesg(regs);
>> +
>>  	/* Caller and Callee regs */
>>  	show_regs(regs);
>>  
>> diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c
>> index b884bbd6f354..d9c6958a1702 100644
>> --- a/arch/arc/mm/fault.c
>> +++ b/arch/arc/mm/fault.c
>> @@ -202,6 +202,7 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
>>  		/* info.si_code has been set above */
>>  		info.si_addr = (void __user *)address;
>>  		force_sig_info(SIGSEGV, &info, tsk);
>> +		show_exception_mesg(regs);
>>  		return;
>>  	}
>>  
>> @@ -241,4 +242,5 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
>>  	info.si_code = BUS_ADRERR;
>>  	info.si_addr = (void __user *)address;
>>  	force_sig_info(SIGBUS, &info, tsk);
>> +	show_exception_mesg(regs);
>>  }