Re: [Libguestfs] [libnbd PATCH] docs: Mention that nbd_close is not thread-safe

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.

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