3.16.52-rc1 review patch. If anyone has any objections, please let me know.
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From: Ravi Bangoria ravi.bangoria@linux.vnet.ibm.com
commit 4917fcb58cc73f6b81455e3c5f960144809ddf1a upstream.
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: 5f6d0380c640 ("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 Signed-off-by: Ben Hutchings ben@decadent.org.uk --- arch/powerpc/perf/core-book3s.c | 5 +++++ 1 file changed, 5 insertions(+)
--- a/arch/powerpc/perf/core-book3s.c +++ b/arch/powerpc/perf/core-book3s.c @@ -755,6 +755,11 @@ 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;