On Sun, 23 Feb 2014, Vince Weaver wrote:
> 
> and as far as I can tell nothing touches rbp again until the segfault.
> Nothing in _memset_sse2 does as far as I can tell.

I only know enough about ftrace to be dangerous, but here is what I think 
is the trace of the problem:

     perf_fuzzer-11492 [000] 197077.488363: function:             
intel_get_event_constraints
     perf_fuzzer-11492 [000] 197077.488363: function:                
intel_pebs_constraints
     perf_fuzzer-11492 [000] 197077.488365: function:             
intel_put_event_constraints
     perf_fuzzer-11492 [000] 197077.488365: function:             
intel_pmu_enable_all
     perf_fuzzer-11492 [000] 197077.488366: function:                
intel_pmu_pebs_enable_all
     perf_fuzzer-11492 [000] 197077.488367: function:                
intel_pmu_lbr_enable_all
     perf_fuzzer-11492 [000] 197077.488366: function:                
intel_pmu_pebs_enable_all
     perf_fuzzer-11492 [000] 197077.488367: function:                
intel_pmu_lbr_enable_all
     perf_fuzzer-11492 [000] 197077.488368: function:             mutex_unlock
     perf_fuzzer-11492 [000] 197077.488368: function:             mutex_lock
     perf_fuzzer-11492 [000] 197077.488369: function:                
_cond_resched
     perf_fuzzer-11492 [000] 197077.488370: function:             
_raw_spin_lock_irq
     perf_fuzzer-11492 [000] 197077.488370: function:             mutex_unlock
     perf_fuzzer-11492 [000] 197077.488371: function:             mutex_lock
     perf_fuzzer-11492 [000] 197077.488371: function:                
_cond_resched
     perf_fuzzer-11492 [000] 197077.488372: function:             
_raw_spin_lock_irq
     perf_fuzzer-11492 [000] 197077.488373: function:             mutex_unlock
     perf_fuzzer-11492 [000] 197077.488373: function:             mutex_lock
     perf_fuzzer-11492 [000] 197077.488374: function:                
_cond_resched
     perf_fuzzer-11492 [000] 197077.488374: function:             
_raw_spin_lock_irq
     perf_fuzzer-11492 [000] 197077.488375: function:             
smp_call_function_single
     perf_fuzzer-11492 [000] 197077.488376: function:             _raw_spin_lock
     perf_fuzzer-11492 [000] 197077.488377: function:             mutex_unlock
     perf_fuzzer-11492 [000] 197077.488378: function:             mutex_lock
     perf_fuzzer-11492 [000] 197077.488378: function:                
_cond_resched
     perf_fuzzer-11492 [000] 197077.488379: function:             
_raw_spin_lock_irq
     perf_fuzzer-11492 [000] 197077.488380: function:             
smp_call_function_single
     perf_fuzzer-11492 [000] 197077.488380: function:             _raw_spin_lock
     perf_fuzzer-11492 [000] 197077.488381: function:             mutex_unlock
     perf_fuzzer-11492 [000] 197077.488382: function:             mutex_unlock
     perf_fuzzer-11492 [000] 197077.488383: function:             
syscall_trace_leave
     perf_fuzzer-11492 [000] 197077.488383: sys_exit:             NR 1073741981 
= 0
     perf_fuzzer-11492 [000] 197077.488387: function:             
do_device_not_available
     perf_fuzzer-11492 [000] 197077.488387: function:                
math_state_restore
     perf_fuzzer-11492 [000] 197077.488390: function:             
trace_do_page_fault
     perf_fuzzer-11492 [000] 197077.488391: page_fault_user:      
address=__per_cpu_end ip=__per_cpu_end error_code=0x6
     perf_fuzzer-11492 [000] 197077.488395: function:             perf_callchain
     perf_fuzzer-11492 [000] 197077.488396: function:             
copy_from_user_nmi
     perf_fuzzer-11492 [000] 197077.488397: function:             
trace_do_page_fault
     perf_fuzzer-11492 [000] 197077.488398: page_fault_kernel:    
address=irq_stack_union ip=copy_user_generic_string error_code=0x0
     perf_fuzzer-11492 [000] 197077.488399: function:                
__do_page_fault
     perf_fuzzer-11492 [000] 197077.488400: function:                   
bad_area_nosemaphore
     perf_fuzzer-11492 [000] 197077.488401: function:                      
__bad_area_nosemaphore
     perf_fuzzer-11492 [000] 197077.488401: function:                         
no_context
     perf_fuzzer-11492 [000] 197077.488402: function:                           
 fixup_exception
     perf_fuzzer-11492 [000] 197077.488403: function:                           
    search_exception_tables
     perf_fuzzer-11492 [000] 197077.488403: function:                           
       search_extable
     perf_fuzzer-11492 [000] 197077.488405: function:             
copy_user_handle_tail
     perf_fuzzer-11492 [000] 197077.488406: function:             
trace_do_page_fault
     perf_fuzzer-11492 [000] 197077.488406: page_fault_kernel:    
address=irq_stack_union ip=copy_user_handle_tail error_code=0x0
     perf_fuzzer-11492 [000] 197077.488407: function:                
__do_page_fault
     perf_fuzzer-11492 [000] 197077.488408: function:                   
bad_area_nosemaphore
     perf_fuzzer-11492 [000] 197077.488409: function:                      
__bad_area_nosemaphore
     perf_fuzzer-11492 [000] 197077.488409: function:                         
no_context
     perf_fuzzer-11492 [000] 197077.488410: function:                           
 fixup_exception
     perf_fuzzer-11492 [000] 197077.488410: function:                           
    search_exception_tables
     perf_fuzzer-11492 [000] 197077.488411: function:                           
       search_extable
     perf_fuzzer-11492 [000] 197077.488413: function:             
perf_output_begin
     perf_fuzzer-11492 [000] 197077.488414: function:             
perf_output_copy
     perf_fuzzer-11492 [000] 197077.488415: function:             
perf_output_copy
     perf_fuzzer-11492 [000] 197077.488415: function:             
perf_output_copy
     perf_fuzzer-11492 [000] 197077.488416: function:             
perf_output_copy
     perf_fuzzer-11492 [000] 197077.488418: function:             
perf_output_copy
     perf_fuzzer-11492 [000] 197077.488419: function:             
perf_output_copy
     perf_fuzzer-11492 [000] 197077.488419: function:             
perf_output_end
     perf_fuzzer-11492 [000] 197077.488420: function:                
perf_output_put_handle
     perf_fuzzer-11492 [000] 197077.488421: function:             
__do_page_fault
     perf_fuzzer-11492 [000] 197077.488422: function:                
down_read_trylock
     perf_fuzzer-11492 [000] 197077.488423: function:                
_cond_resched
     perf_fuzzer-11492 [000] 197077.488423: function:                find_vma
     perf_fuzzer-11492 [000] 197077.488424: function:                bad_area
     perf_fuzzer-11492 [000] 197077.488425: function:                   up_read
     perf_fuzzer-11492 [000] 197077.488426: function:                   
__bad_area_nosemaphore
     perf_fuzzer-11492 [000] 197077.488426: function:                      
is_prefetch
     perf_fuzzer-11492 [000] 197077.488427: function:                         
convert_ip_to_linear
     perf_fuzzer-11492 [000] 197077.488428: function:                      
unhandled_signal
     perf_fuzzer-11492 [000] 197077.488429: function:                      
__printk_ratelimit
     perf_fuzzer-11492 [000] 197077.488430: function:             
_raw_spin_trylock
     perf_fuzzer-11492 [000] 197077.488430: function:             
_raw_spin_unlock_irqrestore
     perf_fuzzer-11492 [000] 197077.488431: function:                      
printk
     perf_fuzzer-11492 [000] 197077.488432: function:                         
vprintk_emit
     perf_fuzzer-11492 [000] 197077.488434: function:                           
 _raw_spin_lock
     perf_fuzzer-11492 [000] 197077.488443: function:                           
 cont_add
     perf_fuzzer-11492 [000] 197077.488444: function:                           
 console_trylock
     perf_fuzzer-11492 [000] 197077.488445: function:                           
    down_trylock
     perf_fuzzer-11492 [000] 197077.488445: function:                           
       _raw_spin_lock_irqsave
     perf_fuzzer-11492 [000] 197077.488446: function:                           
       _raw_spin_unlock_irqrestore
     perf_fuzzer-11492 [000] 197077.488447: function:                           
 console_unlock
     perf_fuzzer-11492 [000] 197077.488447: function:                           
    _raw_spin_lock_irqsave
     perf_fuzzer-11492 [000] 197077.488449: function:                           
    print_time
     perf_fuzzer-11492 [000] 197077.488452: function:                           
    T.950
     perf_fuzzer-11492 [000] 197077.488453: console:              
[197179.420735] perf_fuzzer[11492]: segfault at 22e0 ip 000000000041efab sp 
00000000ffda0938 error 6
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