redis#14072) Compiled Redis with COVERAGE_TEST, while using the fork API encountered the following issue: - Forked process calls `RedisModule_ExitFromChild` - child process starts to report its COW while performing IO operations - Parent process terminates child process with `RedisModule_KillForkChild` - Child process signal handler gets called while an IO operation is called - exit() is called because COVERAGE_TEST was on during compilation. - exit() tries to perform more IO operations in its exit handlers. - process gets deadlocked Backtrace snippet: ``` #0 futex_wait (private=0, expected=2, futex_word=0x7e1220000c50) at ../sysdeps/nptl/futex-internal.h:146 #1 __GI___lll_lock_wait_private (futex=0x7e1220000c50) at ./nptl/lowlevellock.c:34 #2 0x00007e1234696429 in __GI__IO_flush_all () at ./libio/genops.c:698 #3 0x00007e123469680d in _IO_cleanup () at ./libio/genops.c:843 #4 0x00007e1234647b74 in __run_exit_handlers (status=status@entry=255, listp=<optimized out>, run_list_atexit=run_list_atexit@entry=true, run_dtors=run_dtors@entry=true) at ./stdlib/exit.c:129 #5 0x00007e1234647bbe in __GI_exit (status=status@entry=255) at ./stdlib/exit.c:138 #6 0x00005ef753264e13 in exitFromChild (retcode=255) at /home/jonathan/CLionProjects/redis/src/server.c:263 #7 sigKillChildHandler (sig=<optimized out>) at /home/jonathan/CLionProjects/redis/src/server.c:6794 #8 <signal handler called> #9 0x00007e1234685b94 in _IO_fgets (buf=buf@entry=0x7e122dafdd90 "KSM:", ' ' <repeats 19 times>, "0 kB\n", n=n@entry=1024, fp=fp@entry=0x7e1220000b70) at ./libio/iofgets.c:47 #10 0x00005ef75326c5e0 in fgets (__stream=<optimized out>, __n=<optimized out>, __s=<optimized out>, __s=<optimized out>, __n=<optimized out>, __stream=<optimized out>) at /usr/include/x86_64-linux-gnu/bits/stdio2.h:200 #11 zmalloc_get_smap_bytes_by_field (field=0x5ef7534c42fd "Private_Dirty:", pid=<optimized out>) at /home/jonathan/CLionProjects/redis/src/zmalloc.c:928 #12 0x00005ef75338ab1f in zmalloc_get_private_dirty (pid=-1) at /home/jonathan/CLionProjects/redis/src/zmalloc.c:978 #13 sendChildInfoGeneric (info_type=CHILD_INFO_TYPE_MODULE_COW_SIZE, keys=0, progress=-1, pname=0x5ef7534c95b2 "Module fork") at /home/jonathan/CLionProjects/redis/src/childinfo.c:71 #14 0x00005ef75337962c in sendChildCowInfo (pname=0x5ef7534c95b2 "Module fork", info_type=CHILD_INFO_TYPE_MODULE_COW_SIZE) at /home/jonathan/CLionProjects/redis/src/server.c:6895 #15 RM_ExitFromChild (retcode=0) at /home/jonathan/CLionProjects/redis/src/module.c:11468 ``` Change is to make the exit() _exit() calls conditional based on a parameter to exitFromChild function. The signal handler should exit without io operations since it doesn't know its history.(If we were in the middle of IO operations before it was called) --------- Co-authored-by: Yuan Wang <wangyuancode@163.com>

Used Sentinel Debug command to reduce the test time #14

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