[Bug libc/14267] New: fprintf() function is multithread-unsafe

[penght at cn dot fujitsu.com]

http://sourceware.org/bugzilla/show_bug.cgi?id=14267

             Bug #: 14267
           Summary: fprintf() function is multithread-unsafe
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
        AssignedTo: unassigned@sourceware.org
        ReportedBy: penght@cn.fujitsu.com
                CC: carlos@systemhalted.org, drepper.fsp@gmail.com
    Classification: Unclassified


Created attachment 6460
  --> http://sourceware.org/bugzilla/attachment.cgi?id=6460
The Patch can make fprintf() function to multithread-safe

fprintf() uses static variables __printf_function_table and
__printf_va_arg_table indirectly, which are not protected. It is
not safe in multithread circumstance.

When call fprintf() and register_printf_specifier() simultaneously
in multithread circumstance, the following case will cause unsafe.
The case has two threads: A and B.

a. thread B call register_printf_specifier('W', print_widget,
print_widget_arginfo)
b. thread A call fprintf (stdout, "|%W|\n", &mywidget), when judge
   __printf_function_table is not NULL, but not output &mywidget
c. thread B call register_printf_specifier('W', NULL, NULL)
d. thread A output &mywidget when __printf_function_table is NULL
e. programme will Segmentation fault

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