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

From: Ravi Bangoria
Date: Tue Sep 19 2017 - 02:17:25 EST


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@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Kamalesh Babulal <kamalesh@xxxxxxxxxxxxxxxxxx>
---
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