SIGBUS and hang in dl* functions after truncate

[Florian Weimer]

* Justin Fries via Libc-help:

> I thought I would inquire to see whether glibc could avoid the SIGBUS
> as on those other systems, or failing that whether I can handle the
> SIGBUS in a way that lets glibc release its locks, currently elided by
> my use of siglongjmp() as shown in the attached test case.  Thanks in
> advance for any advice you can share.

We already set MAP_DENYWRITE in an attempt to make this scenario
impossible.  Some very old kernels indeed refused to modify the shared
object with ETXTBSY, but this functionality was removed from the Linux
kernel.

Some background is available here:

  The shrinking role of ETXTBSY
  <https://lwn.net/Articles/866493/>

Thanks,
Florian