MySQL Bugs: #85076: handle_fatal_signal calls unsafe function pthread_getspecific

Bug #85076	handle_fatal_signal calls unsafe function pthread_getspecific - it can crash
Submitted:	20 Feb 2017 7:14
Reporter:	Shane Bester (Platinum Quality Contributor)	Email Updates:
Status:	Verified	Impact on me:	None
Category:	MySQL Server: Errors	Severity:	S3 (Non-critical)
Version:	5.6	OS:	Linux (x64)
Assigned to:		CPU Architecture:	Any

Description:
This is a followup to https://bugs.mysql.com/bug.php?id=54082
Signal handler can crash here:

5.6.19:
(gdb) bt
#0  in __GI___pthread_getspecific (key=3) at pthread_getspecific.c:56
#1  in _current_thd () at ./sql/mysqld.h:749
#2  in handle_fatal_signal (sig=11) at ./sql/signal_handler.cc:152
#3  <signal handler called>
#4  in __GI___pthread_getspecific (key=3) at pthread_getspecific.c:56
#5  in _current_thd () at ./sql/mysqld.h:749
#6  in decimal_operation_results (result=2) at ./sql/my_decimal.cc:48
#7  in check_result (mask=30, result=816) at ./sql/my_decimal.h:224
#8  in my_decimal2int at ./sql/my_decimal.h:379
#9  in user_var_entry::val_int at ./sql/item_func.cc:4845
#10 0x0000000000099023 in ?? ()
#11 0x0000000000000000 in ?? ()

The line of code crashing is :     THD *thd=current_thd;

How to repeat:
not readily repeatable. happens randomly on crashes.

Suggested fix:
I am really not sure, but this is documenting the problem exists..

fwiw,  backtrace() shouldn't be called either as it's not signal-safe, but I think we need to use this for ease of use to study log files.

http://pubs.opengroup.org/onlinepubs/009695399/functions/xsh_chap02_04.html

here is an example of backtrace() crashing in the signal handler:

(gdb) bt
#0  in ?? () from /lib64/libgcc_s.so.1
#1  in _Unwind_Backtrace () from /lib64/libgcc_s.so.1
#2  in __GI___backtrace (array=<optimized out>, size=128) at ../sysdeps/x86_64/backtrace.c:109
#3  in my_print_stacktrace (stack_bottom=0x7f8df8a06e48 "", thread_stack=262144) at ./mysys/stacktrace.c:224
#4  in handle_fatal_signal (sig=11) at ./sql/signal_handler.cc:162
#5  <signal handler called>
#6  0x000000000166312c in ?? ()
#7  0x6574616765726700 in ?? ()
#8  0x0000000000002b21 in ?? ()
#9  0x2e20363100200064 in ?? ()
#10 0x0000000000000000 in ?? ()