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powerpc/sysrq: Fix oops whem ppmu is not registered 

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

Fixes: 5f6d0380c6 ("powerpc/perf: Define perf_event_print_debug() to print PMU register values")
Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Ravi Bangoria 2017-09-19 11:47:06 +05:30 committed by Michael Ellerman
parent 8632ec8cdc
commit 4917fcb58c
1 changed files with 5 additions and 0 deletions
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5
arch/powerpc/perf/core-book3s.c
View File

@ -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;