On Mon, 2024-04-29 at 18:25 -0700, Dan Williams wrote:
> Vishal Verma wrote:
> > Commit c05ae9d85b47 ("dax/bus.c: replace driver-core lock usage by a local
> > rwsem")
> > was a bit overzealous in eliminating device_lock() usage, and ended up
> > removing a couple of lock acquisitions which were needed, and as a
> > result, fix some of the conditional locking missteps that the above
> > commit introduced in unregister_dax_dev() and unregister_dax_mapping().
>
> I think it makes sense to tell the story a bit about why the
> delete_store() conversion was problematic, because the
> unregister_dev_dax() changes were just a knock-on effect to fixing the
> delete_store() flow.
>
> Something like:
>
> ---
> commit c05ae9d85b47 ("dax/bus.c: replace driver-core lock usage by a local
> rwsem")
> aimed to undo device_lock() abuses for protecting changes to dax-driver
> internal data-structures like the dax_region resource tree to
> device-dax-instance range structures. However, the device_lock() was
> legitamately
> enforcing that devices to be deleted were not current actively attached
> to any driver nor assigned any capacity from the region.
> ---
>
> ...you can fill in a couple notes about the knock-on fixups after that
> was restored.
Sounds good, updated!
>
> >
> > @@ -560,15 +551,12 @@ static ssize_t delete_store(struct device *dev,
> > struct device_attribute *attr,
> > if (!victim)
> > return -ENXIO;
> >
> > - rc = down_write_killable(&dax_region_rwsem);
> > - if (rc)
> > - return rc;
> > - rc = down_write_killable(&dax_dev_rwsem);
> > - if (rc) {
> > - up_write(&dax_region_rwsem);
> > - return rc;
> > - }
> > + device_lock(dev);
> > + device_lock(victim);
> > dev_dax = to_dev_dax(victim);
> > + rc = down_write_killable(&dax_dev_rwsem);
>
> This begs the question, why down_write_killable(), but not
> device_lock_interruptible()?
Do you mean change the device_lock()s to device_lock_interruptible() in
addition to the taking the rwsem (i.e. not instead of the rwsem..)?
I guess I just restored what was there previously - but the
interruptible variant makes sense, I can make that change.
>
> I do not expect any of this is long running so likely down_write() is
> sufficient here, especially since the heaviest locks to acquire are
> already held by the time rwsem is considered.
>
> Other than that this looks good to me:
>
> You can include my Reviewed-by on the next posting.
Thanks for the review Dan!
