On Thu, Jul 25, 2019 at 10:56:02AM +0200, Martin Kletzander wrote:
On Thu, Jul 25, 2019 at 09:41:01AM +0100, Richard W.M. Jones wrote:
On Wed, Jul 24, 2019 at 03:14:28PM -0500, Eric Blake wrote:
Closing the handle in one thread while another thread is locked causes undefined behavior (as closing does not obtain a lock, and can cause use-after-free or other nasty problems to the thread that does own the lock). However, it is not sensible to try and obtain a lock in nbd_close, as POSIX says that it is also undefined for any other thread to wait on a mutex that has already been destroyed. Therefore, we don't need to change our code, but merely remind users that nbd_close is not safe until all other uses of the handle have ceased. ---
generator/generator | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/generator/generator b/generator/generator index 896ad2a..bdd8fd7 100755 --- a/generator/generator +++ b/generator/generator @@ -3532,7 +3532,8 @@ for how to get further details of the error. Closes the handle and frees any associated resources. The final status of any command that has not been retired (whether by C<nbd_aio_command_completed> or by a low-level completion callback -returning C<1>) is lost. +returning C<1>) is lost. This function is not safe to call while +any other thread is still using any C<nbd_*> API on the same handle.
=head1 GETTING THE LATEST ERROR MESSAGE IN THE THREAD
ACK.
Yes it's not safe to call nbd_close until all other uses of the same handle from any other thread are over.
Would it be too much of a trouble to add reference counting and give users a way to "copy" of the handle? It wouldn't be a copy, but merely an increment on the reference counter. Or is it not worth doing that?
Reference counting is a huge PITA as well as making it much harder to correctly write bindings in other languages, so I'd greatly prefer not to do this. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com Fedora Windows cross-compiler. Compile Windows programs, test, and build Windows installers. Over 100 libraries supported. http://fedoraproject.org/wiki/MinGW