[Bug libc/4737] fork is not async-signal-safe

["morten+sources dot redhat dot com at afdelingp dot dk" <sourceware-bugzilla at sourceware dot org>]

------- Additional Comments From morten+sources dot redhat dot com at afdelingp dot dk  2008-11-07 01:08 -------
It is, as far as I can see, not a problem of the fork() implementation
allocating memory. I believe that it's:

1) a problem of glibc's malloc() implementation registering ptmalloc_lock_all()
for execution at fork (via thread_atfork()) while not making sure that this
function can actually be called from a signal handler without deadlocking.
Fork() just calls each registered function. It can not, in any way, know if
these functions will lock up the process - that is the responsibility of whoever
registers a the function for execution. This must be a bug in malloc/arena.c.
This is the bug you (Nicholas) hit.

2) a problem of fork() calling _IO_list_lock() which might be locked by the main
execution flow. This must be a bug in nptl/sysdeps/unix/sysv/linux/fork.c. This
is the bug I hit.

I think it looks like two separate bugs, which are triggered by similar
conditions. The fix might be identical; I don't know.

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http://sourceware.org/bugzilla/show_bug.cgi?id=4737

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