Robust mutexes acquired at the time of a call to fork() do not remain
acquired by the forked child process. We have to clear the list of
acquired robust mutexes before registering this list with the kernel;
otherwise, if some of the robust mutexes are process-shared, the parent
process can alter the child's robust mutex list, which can lead to
deadlocks or even modification of memory that may not be occupied by a
mutex anymore.
[BZ #19402]
* sysdeps/nptl/fork.c (__libc_fork): Clear list of acquired robust
mutexes.
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