[dm-devel] [PATCH 05/35] libmultipath: improve cleanup of uevent queues on exit

[Martin Wilck]

On Wed, 2021-09-15 at 17:20 -0500, Benjamin Marzinski wrote:
> On Fri, Sep 10, 2021 at 01:40:50PM +0200, mwilck at suse.com wrote:
> > From: Martin Wilck <mwilck at suse.com>
> > 
> > uevents listed on merge_node must be cleaned up, too. uevents
> > cancelled while being serviced and temporary queues, likewise.
> > The global uevq must be cleaned out in the uevent listener thread,
> > because it might have added events after the dispatcher thread
> > had already finished.
> > 
> 
> There's nothing wrong with this, but for the global list, wouldn't it
> be
> easier to just wait till after cleanup_child() calls
> cleanup_threads(),
> and then call cleanup_global_uevq(). That way you know nothing else
> is
> running.

That would be possible. If I understand your proposal correctly, that
would require calling cleanup_global_uevq() from cleanup_child(), i.e.
from the main process. Currently uevq and the functions handling it are
static and only visible in uevent.c.

By taking the lock in cleanup_global_uevq() and calling it from the
listener on cleanup, I can be sure that the dispatcher won't see any
more uevents if it hasn't terminated yet, and that no no events will be
added to the queue after cleanup. So I think with this patch I can also
be certain that uevq is cleaned up for good, without a need to export
the cleanup function, and without enforcing a certain order of thread
shutdowns on exit. Do you disagree?

Thanks,
Martin