[Bug 241059] random kernel panics

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=241059

--- Comment #4 from Mark Johnston <markj at FreeBSD.org> ---
This particular crash was caused by a bit-flip.  %rcx contains a direct map
address with one of the upper bits set to 0:

...
   0xffffffff81098b43 <+1267>:  jmp    0xffffffff81098bc0
<pmap_remove_pages+1392>
   0xffffffff81098b45 <+1269>:  add    $0xffffffffffffffff,%rax                 
   0xffffffff81098b49 <+1273>:  mov    %rax,0x78(%r8)                           
   0xffffffff81098b4d <+1277>:  mov    0x48(%rdx,%rbx,8),%rax                   
   0xffffffff81098b52 <+1282>:  mov    %rsi,%rcx             
   0xffffffff81098b55 <+1285>:  add    $0x40,%rcx                  
   0xffffffff81098b59 <+1289>:  test   %rax,%rax                                
   0xffffffff81098b5c <+1292>:  lea    0x10(%rax),%rax                          
   0xffffffff81098b60 <+1296>:  cmove  %rcx,%rax                                
   0xffffffff81098b64 <+1300>:  mov    0x50(%rdx,%rbx,8),%rcx                   
   0xffffffff81098b69 <+1305>:  mov    %rcx,(%rax)                             
   0xffffffff81098b6c <+1308>:  mov    0x48(%rdx,%rbx,8),%rax                   
   0xffffffff81098b71 <+1313>:  mov    0x50(%rdx,%rbx,8),%rcx                  
=> 0xffffffff81098b76 <+1318>:  mov    %rax,(%rcx)                              
...

(kgdb) info reg
rax            0x0                 0
rbx            0x1e0               480
rcx            0xf7fff802c4df2d20  -576469536503550688
                  ^
rdx            0xfffff806af211000  -8767385038848
rsi            0xfffff807f0b673f0  -8761989762064
rdi            0xffffffff81a49240  -2119921088
rbp            0xfffffe009c39e8c0  0xfffffe009c39e8c0
rsp            0xfffffe009c39e7e0  0xfffffe009c39e7e0

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