From: Dan Williams <dan.j.williams@intel.com>
To: Ben Widawsky <ben.widawsky@intel.com>
Cc: linux-cxl@vger.kernel.org, patches@lists.linux.dev,
Alison Schofield <alison.schofield@intel.com>,
Ira Weiny <ira.weiny@intel.com>,
Jonathan Cameron <Jonathan.Cameron@huawei.com>,
Vishal Verma <vishal.l.verma@intel.com>,
Bjorn Helgaas <helgaas@kernel.org>,
Linux NVDIMM <nvdimm@lists.linux.dev>,
Linux PCI <linux-pci@vger.kernel.org>
Subject: Re: [PATCH v5 01/15] cxl/region: Add region creation ABI
Date: Thu, 17 Feb 2022 12:26:58 -0800 [thread overview]
Message-ID: <CAPcyv4in9Pby8X8ydCLH8SOhr3pjYM7UCAbTOHzuMkKmax8M=Q@mail.gmail.com> (raw)
In-Reply-To: <20220217185811.qjct4dlnupgah7lh@intel.com>
On Thu, Feb 17, 2022 at 10:58 AM Ben Widawsky <ben.widawsky@intel.com> wrote:
>
> On 22-02-17 09:58:04, Dan Williams wrote:
> > On Thu, Feb 17, 2022 at 9:19 AM Ben Widawsky <ben.widawsky@intel.com> wrote:
> > >
> > > Regions are created as a child of the decoder that encompasses an
> > > address space with constraints. Regions have a number of attributes that
> > > must be configured before the region can be activated.
> > >
> > > The ABI is not meant to be secure, but is meant to avoid accidental
> > > races. As a result, a buggy process may create a region by name that was
> > > allocated by a different process. However, multiple processes which are
> > > trying not to race with each other shouldn't need special
> > > synchronization to do so.
> > >
> > > // Allocate a new region name
> > > region=$(cat /sys/bus/cxl/devices/decoder0.0/create_region)
> > >
> > > // Create a new region by name
> > > while
> > > region=$(cat /sys/bus/cxl/devices/decoder0.0/create_region)
> > > ! echo $region > /sys/bus/cxl/devices/decoder0.0/create_region
> > > do true; done
> > >
> > > // Region now exists in sysfs
> > > stat -t /sys/bus/cxl/devices/decoder0.0/$region
> > >
> > > // Delete the region, and name
> > > echo $region > /sys/bus/cxl/devices/decoder0.0/delete_region
> > >
> > > Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
[..]
> > > +static void unregister_region(void *_cxlr)
> > > +{
> > > + struct cxl_region *cxlr = _cxlr;
> > > +
> > > + if (!test_and_set_bit(REGION_DEAD, &cxlr->flags))
> > > + device_unregister(&cxlr->dev);
> >
> > I thought REGION_DEAD was needed to prevent double
> > devm_release_action(), not double unregister?
> >
>
> I believe that's correct, repeating what you said on our internal list:
>
> On 22-02-14 14:11:41, Dan Williams wrote:
> True, you do need to solve the race between multiple writers racing to
> do the unregistration, but that could be done with something like:
>
> if (!test_and_set_bit(REGION_DEAD, &cxlr->flags))
> device_unregister(&cxlr->dev);
>
> So I was just trying to implement what you said. Remainder of the discussion
> below...
That was in the context of moving the unregistration to a workqueue
and taking the device lock to validate whether the device has already
been unbound. In this case keeping the devm_release_action() inline in
the sysfs attribute the flag needs to protect against racing
devm_release_action(). I am not saying that a workqueue is now needed,
just clarifying the context of that suggestion.
[..]
> > > +
> > > + return cxlr;
> > > +
> > > +err_out:
> > > + put_device(dev);
> > > + kfree(cxlr);
> >
> > This is a double-free of cxlr;
> >
>
> Because of release()? How does release get called if the region device wasn't
> added? Or is there something else?
->release() is always called at final put_device() regardless of
whether the device was registered with device_add() or not. I.e. see
all the other dev_set_name() error handling in the core that just does
put_device().
next prev parent reply other threads:[~2022-02-17 20:27 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-28 0:26 [PATCH v3 00/14] CXL Region driver Ben Widawsky
2022-01-28 0:26 ` [PATCH v3 01/14] cxl/region: Add region creation ABI Ben Widawsky
2022-01-28 18:14 ` Dan Williams
2022-01-28 18:59 ` Dan Williams
2022-02-02 18:26 ` Ben Widawsky
2022-02-02 18:28 ` Ben Widawsky
2022-02-02 18:48 ` Ben Widawsky
2022-02-02 19:00 ` Dan Williams
2022-02-02 19:02 ` Ben Widawsky
2022-02-02 19:15 ` Dan Williams
2022-02-01 22:42 ` Ben Widawsky
2022-02-01 15:53 ` Jonathan Cameron
2022-02-17 17:10 ` [PATCH v4 " Ben Widawsky
2022-02-17 17:19 ` [PATCH v5 01/15] " Ben Widawsky
2022-02-17 17:33 ` Ben Widawsky
2022-02-17 17:58 ` Dan Williams
2022-02-17 18:58 ` Ben Widawsky
2022-02-17 20:26 ` Dan Williams [this message]
2022-02-17 22:22 ` Ben Widawsky
2022-02-17 23:32 ` Dan Williams
2022-02-18 16:41 ` Ben Widawsky
2022-01-28 0:26 ` [PATCH v3 02/14] cxl/region: Introduce concept of region configuration Ben Widawsky
2022-01-29 0:25 ` Dan Williams
2022-02-01 14:59 ` Ben Widawsky
2022-02-03 5:06 ` Dan Williams
2022-02-01 23:11 ` Ben Widawsky
2022-02-03 17:48 ` Dan Williams
2022-02-03 22:23 ` Ben Widawsky
2022-02-03 23:27 ` Dan Williams
2022-02-04 0:19 ` Ben Widawsky
2022-02-04 2:45 ` Dan Williams
2022-02-17 18:36 ` Ben Widawsky
2022-02-17 19:57 ` Dan Williams
2022-02-17 20:20 ` Ben Widawsky
2022-02-17 21:12 ` Dan Williams
2022-02-23 21:49 ` Ben Widawsky
2022-02-23 22:24 ` Dan Williams
2022-02-23 22:31 ` Ben Widawsky
2022-02-23 22:42 ` Dan Williams
2022-01-28 0:26 ` [PATCH v3 03/14] cxl/mem: Cache port created by the mem dev Ben Widawsky
2022-02-17 1:20 ` Dan Williams
2022-01-28 0:26 ` [PATCH v3 04/14] cxl/region: Introduce a cxl_region driver Ben Widawsky
2022-02-01 16:21 ` Jonathan Cameron
2022-02-17 6:04 ` Dan Williams
2022-01-28 0:26 ` [PATCH v3 05/14] cxl/acpi: Handle address space allocation Ben Widawsky
2022-02-18 19:17 ` Dan Williams
2022-01-28 0:26 ` [PATCH v3 06/14] cxl/region: Address " Ben Widawsky
2022-02-18 19:51 ` Dan Williams
2022-01-28 0:27 ` [PATCH v3 07/14] cxl/region: Implement XHB verification Ben Widawsky
2022-02-18 20:23 ` Dan Williams
2022-01-28 0:27 ` [PATCH v3 08/14] cxl/region: HB port config verification Ben Widawsky
2022-02-14 16:20 ` Jonathan Cameron
2022-02-14 17:51 ` Ben Widawsky
2022-02-14 18:09 ` Jonathan Cameron
2022-02-15 16:35 ` Jonathan Cameron
2022-02-18 21:04 ` Dan Williams
2022-01-28 0:27 ` [PATCH v3 09/14] cxl/region: Add infrastructure for decoder programming Ben Widawsky
2022-02-01 18:16 ` Jonathan Cameron
2022-02-18 21:53 ` Dan Williams
2022-01-28 0:27 ` [PATCH v3 10/14] cxl/region: Collect host bridge decoders Ben Widawsky
2022-02-01 18:21 ` Jonathan Cameron
2022-02-18 23:42 ` Dan Williams
2022-01-28 0:27 ` [PATCH v3 11/14] cxl/region: Add support for single switch level Ben Widawsky
2022-02-01 18:26 ` Jonathan Cameron
2022-02-15 16:10 ` Jonathan Cameron
2022-02-18 18:23 ` Jonathan Cameron
2022-01-28 0:27 ` [PATCH v3 12/14] cxl: Program decoders for regions Ben Widawsky
2022-02-24 0:08 ` Dan Williams
2022-01-28 0:27 ` [PATCH v3 13/14] cxl/pmem: Convert nvdimm bridge API to use dev Ben Widawsky
2022-01-28 0:27 ` [PATCH v3 14/14] cxl/region: Create an nd_region Ben Widawsky
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