From: Dan Williams <dan.j.williams@intel.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Vishal Verma <vishal.l.verma@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>,
Dave Jiang <dave.jiang@intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
"Oscar Salvador" <osalvador@suse.de>,
<linux-kernel@vger.kernel.org>, <nvdimm@lists.linux.dev>,
<linux-cxl@vger.kernel.org>, David Hildenbrand <david@redhat.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Huang Ying <ying.huang@intel.com>, <linux-mm@kvack.org>,
Joao Martins <joao.m.martins@oracle.com>
Subject: Re: [PATCH v6 2/4] dax/bus: Use guard(device) in sysfs attribute helpers
Date: Fri, 15 Dec 2023 09:15:45 -0800 [thread overview]
Message-ID: <657c89c16d5f5_269bd294bd@dwillia2-mobl3.amr.corp.intel.com.notmuch> (raw)
In-Reply-To: <2023121515-litigate-finished-76dd@gregkh>
Greg Kroah-Hartman wrote:
> On Thu, Dec 14, 2023 at 10:25:27PM -0700, Vishal Verma wrote:
> > Use the guard(device) macro to lock a 'struct device', and unlock it
> > automatically when going out of scope using Scope Based Resource
> > Management semantics. A lot of the sysfs attribute writes in
> > drivers/dax/bus.c benefit from a cleanup using these, so change these
> > where applicable.
>
> Wait, why are you needing to call device_lock() at all here? Why is dax
> special in needing this when no other subsystem requires it?
>
> >
> > Cc: Joao Martins <joao.m.martins@oracle.com>
> > Cc: Dan Williams <dan.j.williams@intel.com>
> > Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
> > ---
> > drivers/dax/bus.c | 143 ++++++++++++++++++++++--------------------------------
> > 1 file changed, 59 insertions(+), 84 deletions(-)
> >
> > diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> > index 1ff1ab5fa105..6226de131d17 100644
> > --- a/drivers/dax/bus.c
> > +++ b/drivers/dax/bus.c
> > @@ -294,13 +294,10 @@ static ssize_t available_size_show(struct device *dev,
> > struct device_attribute *attr, char *buf)
> > {
> > struct dax_region *dax_region = dev_get_drvdata(dev);
> > - unsigned long long size;
> >
> > - device_lock(dev);
> > - size = dax_region_avail_size(dax_region);
> > - device_unlock(dev);
> > + guard(device)(dev);
>
> You have a valid device here, why are you locking it? How can it go
> away? And if it can, shouldn't you have a local lock for it, and not
> abuse the driver core lock?
Yes, this is a driver-core lock abuse written by someone who should have
known better. And yes, a local lock to protect the dax_region resource
tree should replace this. A new rwsem to synchronize all list walks
seems appropriate.
next prev parent reply other threads:[~2023-12-15 17:16 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-15 5:25 [PATCH v6 0/4] Add DAX ABI for memmap_on_memory Vishal Verma
2023-12-15 5:25 ` [PATCH v6 1/4] Documentatiion/ABI: Add ABI documentation for sys-bus-dax Vishal Verma
2023-12-15 5:25 ` [PATCH v6 2/4] dax/bus: Use guard(device) in sysfs attribute helpers Vishal Verma
2023-12-15 5:56 ` Matthew Wilcox
2023-12-15 6:33 ` Verma, Vishal L
2023-12-15 16:14 ` gregkh
2023-12-15 7:27 ` Greg Kroah-Hartman
2023-12-15 17:15 ` Dan Williams [this message]
2023-12-15 17:32 ` Verma, Vishal L
2023-12-15 17:53 ` gregkh
2023-12-19 15:27 ` Jonathan Cameron
2023-12-15 5:25 ` [PATCH v6 3/4] mm/memory_hotplug: export mhp_supports_memmap_on_memory() Vishal Verma
2023-12-15 5:25 ` [PATCH v6 4/4] dax: add a sysfs knob to control memmap_on_memory behavior Vishal Verma
2023-12-15 7:53 ` Huang, Ying
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