Messages in this thread Patch in this message | | | Date | Fri, 10 Jan 2014 18:02:24 +0100 | From | Peter Zijlstra <> | Subject | Re: SIGSEGV when using "perf record -g" with 3.13-rc* kernel |
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On Fri, Jan 10, 2014 at 05:58:22PM +0100, Peter Zijlstra wrote: > On Fri, Jan 10, 2014 at 10:29:13AM -0500, Waiman Long wrote: > > Peter, > > > > Call Trace: > > <NMI> [<ffffffff815710af>] dump_stack+0x49/0x62 > > [<ffffffff8104e3bc>] warn_slowpath_common+0x8c/0xc0 > > [<ffffffff8104e40a>] warn_slowpath_null+0x1a/0x20 > > [<ffffffff8105f1f1>] force_sig_info+0x131/0x140 > > [<ffffffff81042a4f>] force_sig_info_fault+0x5f/0x70 > > [<ffffffff8106d8da>] ? search_exception_tables+0x2a/0x50 > > [<ffffffff81043b3d>] ? fixup_exception+0x1d/0x70 > > [<ffffffff81042cc9>] no_context+0x159/0x1f0 > > [<ffffffff81042e8d>] __bad_area_nosemaphore+0x12d/0x230 > > [<ffffffff81042e8d>] ? __bad_area_nosemaphore+0x12d/0x230 > > [<ffffffff81042fa3>] bad_area_nosemaphore+0x13/0x20 > > [<ffffffff81578fc2>] __do_page_fault+0x362/0x480 > > [<ffffffff81578fc2>] ? __do_page_fault+0x362/0x480 > > [<ffffffff815791be>] do_page_fault+0xe/0x10 > > [<ffffffff81575962>] page_fault+0x22/0x30 > > [<ffffffff815817e4>] ? bad_to_user+0x5e/0x66b > > [<ffffffff81285316>] copy_from_user_nmi+0x76/0x90 > > [<ffffffff81017a20>] perf_callchain_user+0xd0/0x360 > > [<ffffffff8111f64f>] perf_callchain+0x1af/0x1f0 > > [<ffffffff81117693>] perf_prepare_sample+0x2f3/0x3a0 > > [<ffffffff8111a2af>] __perf_event_overflow+0x10f/0x220 > > [<ffffffff8111ab14>] perf_event_overflow+0x14/0x20 > > [<ffffffff8101f69e>] intel_pmu_handle_irq+0x1de/0x3c0 > > [<ffffffff81008e44>] ? emulate_vsyscall+0x144/0x390 > > [<ffffffff81576e64>] perf_event_nmi_handler+0x34/0x60 > > [<ffffffff8157664a>] nmi_handle+0x8a/0x170 > > [<ffffffff81576848>] default_do_nmi+0x68/0x210 > > [<ffffffff81576a80>] do_nmi+0x90/0xe0 > > [<ffffffff81575c67>] end_repeat_nmi+0x1e/0x2e > > [<ffffffff81008e44>] ? emulate_vsyscall+0x144/0x390 > > [<ffffffff81008e44>] ? emulate_vsyscall+0x144/0x390 > > [<ffffffff81008e44>] ? emulate_vsyscall+0x144/0x390 > > <<EOE>> [<ffffffff81042f7d>] __bad_area_nosemaphore+0x21d/0x230 > > [<ffffffff81042fa3>] bad_area_nosemaphore+0x13/0x20 > > [<ffffffff81578fc2>] __do_page_fault+0x362/0x480 > > [<ffffffff8113cfbc>] ? vm_mmap_pgoff+0xbc/0xe0 > > [<ffffffff815791be>] do_page_fault+0xe/0x10 > > [<ffffffff81575962>] page_fault+0x22/0x30 > > ---[ end trace 037bf09d279751ec ]--- > > > > So this is a double page faults. Looking at relevant changes in > > 3.13 kernel, I spotted the following one patch that modified the > > perf_callchain_user() function shown up in the stack trace above: > > > > Hurm, that's an expected double fault, not something we should take the > process down for. > > I'll have to look at how all that works for a bit.
How easily can you reproduce this? Could you test something like the below, which would allow us to take double faults from NMI context.
--- arch/x86/mm/fault.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 9ff85bb8dd69..18c498d4274d 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -641,7 +641,7 @@ no_context(struct pt_regs *regs, unsigned long error_code, /* Are we prepared to handle this kernel fault? */ if (fixup_exception(regs)) { - if (current_thread_info()->sig_on_uaccess_error && signal) { + if (!in_nmi() && current_thread_info()->sig_on_uaccess_error && signal) { tsk->thread.trap_nr = X86_TRAP_PF; tsk->thread.error_code = error_code | PF_USER; tsk->thread.cr2 = address;
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