[PATCH] powerpc/sysrq: Fix oops whem ppmu is not registered

[PATCH] powerpc/sysrq: Fix oops whem ppmu is not registered

[Ravi Bangoria]

Kernel crashes if power pmu is not registered and user tries to dump
regs with 'echo p > /proc/sysrq-trigger'. Sample log:

  Unable to handle kernel paging request for data at address 0x00000008
  Faulting instruction address: 0xc0000000000d52f0

  NIP [c0000000000d52f0] perf_event_print_debug+0x10/0x230
  LR [c00000000058a938] sysrq_handle_showregs+0x38/0x50
  Call Trace:
   printk+0x38/0x4c (unreliable)
   __handle_sysrq+0xe4/0x270
   write_sysrq_trigger+0x64/0x80
   proc_reg_write+0x80/0xd0
   __vfs_write+0x40/0x200
   vfs_write+0xc8/0x240
   SyS_write+0x60/0x110
   system_call+0x58/0x6c

Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com> 
---
 arch/powerpc/perf/core-book3s.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index 2e3eb74..9e3da16 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -793,6 +793,11 @@ void perf_event_print_debug(void)
 	u32 pmcs[MAX_HWEVENTS];
 	int i;
 
+	if (!ppmu) {
+		pr_info("Performance monitor hardware not registered.\n");
+		return;
+	}
+
 	if (!ppmu->n_counter)
 		return;
 
-- 
1.8.3.1

Re: [PATCH] powerpc/sysrq: Fix oops whem ppmu is not registered

[Michael Ellerman]

Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com> writes:

> Kernel crashes if power pmu is not registered and user tries to dump
> regs with 'echo p > /proc/sysrq-trigger'. Sample log:
>
>   Unable to handle kernel paging request for data at address 0x00000008
>   Faulting instruction address: 0xc0000000000d52f0
>
>   NIP [c0000000000d52f0] perf_event_print_debug+0x10/0x230
>   LR [c00000000058a938] sysrq_handle_showregs+0x38/0x50
>   Call Trace:
>    printk+0x38/0x4c (unreliable)
>    __handle_sysrq+0xe4/0x270
>    write_sysrq_trigger+0x64/0x80
>    proc_reg_write+0x80/0xd0
>    __vfs_write+0x40/0x200
>    vfs_write+0xc8/0x240
>    SyS_write+0x60/0x110
>    system_call+0x58/0x6c

Thanks.

I added:

  Fixes: 5f6d0380c640 ("powerpc/perf: Define perf_event_print_debug() to print PMU register values")

But I don't think I'll Cc stable, I can't think why we'd ever *not* have
a ppmu registered. How did you hit it?

cheers

Re: [PATCH] powerpc/sysrq: Fix oops whem ppmu is not registered

[Madhavan Srinivasan]

On Tuesday 19 September 2017 03:30 PM, Michael Ellerman wrote:
> Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com> writes:
>
>> Kernel crashes if power pmu is not registered and user tries to dump
>> regs with 'echo p > /proc/sysrq-trigger'. Sample log:
>>
>>    Unable to handle kernel paging request for data at address 0x00000008
>>    Faulting instruction address: 0xc0000000000d52f0
>>
>>    NIP [c0000000000d52f0] perf_event_print_debug+0x10/0x230
>>    LR [c00000000058a938] sysrq_handle_showregs+0x38/0x50
>>    Call Trace:
>>     printk+0x38/0x4c (unreliable)
>>     __handle_sysrq+0xe4/0x270
>>     write_sysrq_trigger+0x64/0x80
>>     proc_reg_write+0x80/0xd0
>>     __vfs_write+0x40/0x200
>>     vfs_write+0xc8/0x240
>>     SyS_write+0x60/0x110
>>     system_call+0x58/0x6c
> Thanks.
>
> I added:
>
>    Fixes: 5f6d0380c640 ("powerpc/perf: Define perf_event_print_debug() to print PMU register values")
>
> But I don't think I'll Cc stable, I can't think why we'd ever *not* have
> a ppmu registered. How did you hit it?
mpe,

We hit this in a compact mode setup where the distro kernel did not have 
the
pmu support for the base pvr.

Maddy


> cheers
>

Re: powerpc/sysrq: Fix oops whem ppmu is not registered

[Michael Ellerman]

On Tue, 2017-09-19 at 06:17:06 UTC, Ravi Bangoria wrote:
> Kernel crashes if power pmu is not registered and user tries to dump
> regs with 'echo p > /proc/sysrq-trigger'. Sample log:
> 
>   Unable to handle kernel paging request for data at address 0x00000008
>   Faulting instruction address: 0xc0000000000d52f0
> 
>   NIP [c0000000000d52f0] perf_event_print_debug+0x10/0x230
>   LR [c00000000058a938] sysrq_handle_showregs+0x38/0x50
>   Call Trace:
>    printk+0x38/0x4c (unreliable)
>    __handle_sysrq+0xe4/0x270
>    write_sysrq_trigger+0x64/0x80
>    proc_reg_write+0x80/0xd0
>    __vfs_write+0x40/0x200
>    vfs_write+0xc8/0x240
>    SyS_write+0x60/0x110
>    system_call+0x58/0x6c
> 
> Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
> Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/4917fcb58cc73f6b81455e3c5f9601

cheers