From bf05fc25f268cd62f147f368fe65ad3e5b04fe9f Mon Sep 17 00:00:00 2001 From: Ravi Bangoria Date: Thu, 15 Jun 2017 19:16:48 +0530 Subject: [PATCH] powerpc/perf: Fix oops when kthread execs user process When a kthread calls call_usermodehelper() the steps are: 1. allocate current->mm 2. load_elf_binary() 3. populate current->thread.regs While doing this, interrupts are not disabled. If there is a perf interrupt in the middle of this process (i.e. step 1 has completed but not yet reached to step 3) and if perf tries to read userspace regs, kernel oops with following log: Unable to handle kernel paging request for data at address 0x00000000 Faulting instruction address: 0xc0000000000da0fc ... Call Trace: perf_output_sample_regs+0x6c/0xd0 perf_output_sample+0x4e4/0x830 perf_event_output_forward+0x64/0x90 __perf_event_overflow+0x8c/0x1e0 record_and_restart+0x220/0x5c0 perf_event_interrupt+0x2d8/0x4d0 performance_monitor_exception+0x54/0x70 performance_monitor_common+0x158/0x160 --- interrupt: f01 at avtab_search_node+0x150/0x1a0 LR = avtab_search_node+0x100/0x1a0 ... load_elf_binary+0x6e8/0x15a0 search_binary_handler+0xe8/0x290 do_execveat_common.isra.14+0x5f4/0x840 call_usermodehelper_exec_async+0x170/0x210 ret_from_kernel_thread+0x5c/0x7c Fix it by setting abi to PERF_SAMPLE_REGS_ABI_NONE when userspace pt_regs are not set. Fixes: ed4a4ef85cf5 ("powerpc/perf: Add support for sampling interrupt register state") Cc: stable@vger.kernel.org # v4.7+ Signed-off-by: Ravi Bangoria Acked-by: Naveen N. Rao Signed-off-by: Michael Ellerman --- arch/powerpc/perf/perf_regs.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/perf/perf_regs.c b/arch/powerpc/perf/perf_regs.c index cbd82fde5770..09ceea6175ba 100644 --- a/arch/powerpc/perf/perf_regs.c +++ b/arch/powerpc/perf/perf_regs.c @@ -101,5 +101,6 @@ void perf_get_regs_user(struct perf_regs *regs_user, struct pt_regs *regs_user_copy) { regs_user->regs = task_pt_regs(current); - regs_user->abi = perf_reg_abi(current); + regs_user->abi = (regs_user->regs) ? perf_reg_abi(current) : + PERF_SAMPLE_REGS_ABI_NONE; } -- 2.20.1