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      1  Bug Id: 4095849
      2  Category: kernel
      3  Subcategory: syscall
      4  State: evaluated
      5  Synopsis: time_constant value >6 with PLL in use leads to integer divide
      6            zero trap panic
      7  Description:
      8 If the time_constant parameter is 7 or higher, and the phase-lock looping model
      9 is in use, the system will take a "integer divide zero trap" panic in
     10 the clock routine as soon as the time_offset becomes non-zero.
     11 
     12 time_constant defaults to 0.  The only place it is set is in the ntp_adjtime
     13 system call, from the 'constant' element of the timex structure argument.
     14 
     15  Work around:
     16 Never set the constant element of the timex structure passed to ntp_adjtime to
     17 a value larger than 6.
     18 
     19 satish.mynam@Eng 1998-04-30
     20 1. Use Sun's version of NTP software instead of PD version. This problem
     21 is not seen with Sun's NTP version (which is mostly eqivalent to PD NTP 3.4
     22 plus some Sun's local functionality futures).
     23 
     24 2. Workaround for the public domain NTP version  ONLY:
     25  =====================================================
     26 The workaround for public domain NTP version is to disable the
     27 KERNEL_PLL from the NTP code. This way ntp_Adjtime() system call is
     28 totally bypassed without sacrificing any of the functionality of the
     29 NTP. The only hit you might see is the way  kernel precision timminig
     30 is done without the PLL algorithm in the kernel.
     31 
     32     The easiest way to disable ntp_adjtime option is(without changing
     33     any makefiles or other config files) to disable the KERNEL_PLL
     34     value in the ./config.h file.
     35 
     36 After doing a ./configure for probing for all the necessary tools(compilers,
     37 os version, libraries),  please comment out KERNEL_PLL macro in
     38 the ./config.h  file.  This will disable the KERNEL_PLL part of the source
     39 code and the newly obtained xntpd is just similar to the old one but it
     40 does not use ntp_adjtime() system call. This prevents it from panic'ng
     41 the kernel.
     42 
     43 /*#define KERNEL_PLL 1*/
     44 
     45 I complied a new xntpd binary this way and it does nothave any ntp_adjtime()
     46 related stuff.
     47 
     48 Default:
     49 =======
     50 /net/divya/export/home/mynam/public_domain/ntp/xntp3-5.92/xntpd>strings
     51 xntpd |
     52 grep ntp_adjtime
     53 354:adj_frequency: ntp_adjtime failed: %m
     54 357:loop_config: ntp_adjtime() failed: %m
     55 435:get_kernel_info: ntp_adjtime() failed: %m
     56 
     57 With KERNEL_PLL disabled in config.h file
     58 -=======================
     59 
     60 /net/divya/export/home/mynam/public_domain/ntp/xntp3-5.92/xntpd>strings
     61 xntpd.nopll | grep ntp_adjtime
     62 
     63         Integrated in releases:
     64  Duplicate of:
     65  Patch id:
     66  See also: 4133517
     67  Summary:
     68 If the time_constant parameter is 7 or higher, and the phase-lock looping model
     69 is in use, the system will take a "integer divide zero trap" panic in
     70 the clock routine as soon as the time_offset becomes non-zero.
     71 
     72 time_constant defaults to 0.  The only place it is set is in the ntp_adjtime
     73 system call, from the 'constant' element of the timex structure argument.
     74 ----------------------------------------------------------------------------
     75