Messages in this thread | | | Date | Fri, 10 Jan 2014 14:43:41 -0500 | From | Waiman Long <> | Subject | Re: SIGSEGV when using "perf record -g" with 3.13-rc* kernel |
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On 01/10/2014 01:54 PM, Andy Lutomirski wrote: > On Fri, Jan 10, 2014 at 9:41 AM, Peter Zijlstra<peterz@infradead.org> wrote: >> On Fri, Jan 10, 2014 at 06:02:23PM +0100, Peter Zijlstra wrote: >>> 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. >> Andy, introduced all this in 4fc3490114bb ("x86-64: Set siginfo and >> context on vsyscall emulation faults"). >> >> It looks like your initial userspace fault hit the magic button and ends >> up in emulate_vsyscall. Right at that point we trigger a PMI, which >> tries to do a stack-trace. That stack-trace also stumbles into unmapped >> memory (might be the same) and faults again. >> >> Now at that point, we usually just give up on the callchain and proceed >> like normal, however because of this double fault emulate-vsyscall >> SIGSEGV magic you loose. >> >> So the below might well be a valid fix.. Anybody? Andy? > Yuck -- when I wrote that thing, I hadn't imagined that an interrupt > (there's nothing particularly special about NMIs here, I think) would > try to access user memory. The fix below looks okay, but IMO it needs > a big fat comment explaining what's going on. > > Is there a way to ask whether the previous entry into the kernel came > from user space? The valid "sig_on_uaccess_error" case happens when > the current fault was triggered by a fault from userspace. The > invalid case (and any invalid case from, say, an int3 that a > tracepoint stuck in there) would be a page fault triggered by a fault > handler that in turn started in kernel space (in particular, in > emulate_vsyscall).
The processes that got the SIGSEGV were all running shell scripts. I am not totally sure that they were running in user space when getting the PMIs, but are likely the case.
-Longman
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