Re: tsan: t5400: set_try_to_free_routine

On 15 August 2017 at 19:35, Stefan Beller [off-list ref] wrote:

On Tue, Aug 15, 2017 at 5:53 AM, Martin Ågren [off-list ref] wrote:

quoted

Using SANITIZE=thread made t5400-send-pack.sh hit the potential race
below.

This is set_try_to_free_routine in wrapper.c. The race relates to the
reading of the "old" value. The caller doesn't care about the "old"
value, so this should be harmless right now. But it seems that using
this mechanism from multiple threads and restoring the earlier value
will probably not work out every time. (Not necessarily because of the
race in set_try_to_free_routine, but, e.g., because callers might not
restore the function pointer in the reverse order of how they
originally set it.)

Properly "fixing" this for thread-safety would probably require some
redesigning, which at the time might not be warranted. I'm just posting
this for completeness.

Maybe related read (also error handling in threads):
https://public-inbox.org/git/20170619220036.22656-1-avarab@gmail.com/

Thanks for the pointer. Threading is tricky business, indeed. I still
haven't entirely groked all the users of set_try_to_free_routine, i.e.,
what they want to avoid and what they want to achieve. I'm just happy
that the only user which cares about the old value is not threaded, to
the best of my understanding.