From: "Verma, Vishal L" <vishal.l.verma@intel.com>
To: "Williams, Dan J" <dan.j.williams@intel.com>,
"Jiang, Dave" <dave.jiang@intel.com>,
"Schofield, Alison" <alison.schofield@intel.com>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>,
"linux-cxl@vger.kernel.org" <linux-cxl@vger.kernel.org>,
"nvdimm@lists.linux.dev" <nvdimm@lists.linux.dev>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 2/4] dax/bus.c: fix locking for unregister_dax_dev / unregister_dax_mapping paths
Date: Tue, 30 Apr 2024 04:11:39 +0000 [thread overview]
Message-ID: <d4047d21f0b88c5baee9140adb56e86afca24b3a.camel@intel.com> (raw)
In-Reply-To: <6630487879c61_148729427@dwillia2-mobl3.amr.corp.intel.com.notmuch>
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!
next prev parent reply other threads:[~2024-04-30 4:11 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-16 21:46 [PATCH v2 0/4] dax/bus.c: Fixups for dax-bus locking Vishal Verma
2024-04-16 21:46 ` [PATCH v2 1/4] dax/bus.c: replace WARN_ON_ONCE() with lockdep asserts Vishal Verma
2024-04-30 1:23 ` Dan Williams
2024-04-16 21:46 ` [PATCH v2 2/4] dax/bus.c: fix locking for unregister_dax_dev / unregister_dax_mapping paths Vishal Verma
2024-04-30 1:25 ` Dan Williams
2024-04-30 4:11 ` Verma, Vishal L [this message]
2024-04-30 5:25 ` Dan Williams
2024-04-16 21:46 ` [PATCH v2 3/4] dax/bus.c: Don't use down_write_killable for non-user processes Vishal Verma
2024-04-30 1:25 ` Dan Williams
2024-04-16 21:46 ` [PATCH v2 4/4] dax/bus.c: Use the right locking mode (read vs write) in size_show Vishal Verma
2024-04-30 1:26 ` Dan Williams
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