[Bug nptl/654] Cancelling nptl thread on dlclose() leads to application hangup

["jakub at redhat dot com" <sourceware-bugzilla@sources.redhat.com>]

------- Additional Comments From jakub at redhat dot com  2005-01-13 13:15 -------
This is the same deadlock as has been fixed by:
2004-07-07  Ulrich Drepper  <drepper@redhat.com>

        * elf/dl-fini.c (_dl_fini): Move the unlock of the ld.so lock
        before the loop running the destructors.
for destructors that are run at exit time.
ATM ld.so holds dl_load_lock when running shared library destructors and the
same lock is used indirectly by libgcc_s.so when unwinding.  If you call
pthread_cancel in a shared library destructor that is run during dlclose,
dl_load_lock is held in the thread calling pthread_cancel, but the cancelled
thread needs to be unwound.  As you also call pthread_join in the same destructor
that waits for the cancelled thread and the cancelled thread is waiting until
dl_load_lock is released (this would happen when dlclose is about to return),
they are deadlocking.

The fix is avoid running shared library destructors with dl_load_lock held,
but that's certainly not trivial.

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http://sources.redhat.com/bugzilla/show_bug.cgi?id=654

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