From: Dan Williams <dan.j.williams@intel.com>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: linux-cxl@vger.kernel.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Vishal L Verma <vishal.l.verma@intel.com>,
"Weiny, Ira" <ira.weiny@intel.com>,
"Schofield, Alison" <alison.schofield@intel.com>
Subject: Re: [PATCH v2 2/4] cxl/mem: Fix synchronization mechanism for device removal vs ioctl operations
Date: Tue, 30 Mar 2021 10:31:15 -0700 [thread overview]
Message-ID: <CAPcyv4ixD=+PejHErT_FLtEyXsm4mk+93R7mQ0uFtd_kd-fs1w@mail.gmail.com> (raw)
In-Reply-To: <20210330170253.GU2356281@nvidia.com>
On Tue, Mar 30, 2021 at 10:03 AM Jason Gunthorpe <jgg@nvidia.com> wrote:
>
> On Tue, Mar 30, 2021 at 09:05:29AM -0700, Dan Williams wrote:
>
> > > If you can't clearly point to the *data* under RCU protection it is
> > > being used wrong.
> >
> > Agree.
> >
> > The data being protected is the value of
> > dev->kobj.state_in_sysfs. The
>
> So where is that read under:
>
> + idx = srcu_read_lock(&cxl_memdev_srcu);
> + rc = __cxl_memdev_ioctl(cxlmd, cmd, arg);
> + srcu_read_unlock(&cxl_memdev_srcu, idx);
>
> ?
device_is_registered() inside __cxl_memdev_ioctl().
> It can't read the RCU protected data outside the RCU critical region,
> and it can't read/write RCU protected data without using the helper
> macros which insert the required barriers.
The required barriers are there. srcu_read_lock() +
device_is_registered() is paired with cdev_device_del() +
synchronize_rcu().
> IMHO this can't use 'dev->kobj.state_in_sysfs' as the RCU protected data.
This usage of srcu is functionally equivalent to replacing
srcu_read_lock() with down_read() and the shutdown path with:
cdev_device_del(...);
down_write(...):
up_write(...);
...to flush readers that read ->state_in_sysfs == 1.
next prev parent reply other threads:[~2021-03-30 17:32 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-30 2:47 [PATCH v2 0/4] cxl/mem: Fix memdev device setup Dan Williams
2021-03-30 2:47 ` [PATCH v2 1/4] cxl/mem: Use sysfs_emit() for attribute show routines Dan Williams
2021-03-30 2:47 ` [PATCH v2 2/4] cxl/mem: Fix synchronization mechanism for device removal vs ioctl operations Dan Williams
2021-03-30 11:16 ` Jason Gunthorpe
2021-03-30 15:37 ` Dan Williams
2021-03-30 15:47 ` Jason Gunthorpe
2021-03-30 16:05 ` Dan Williams
2021-03-30 17:02 ` Jason Gunthorpe
2021-03-30 17:31 ` Dan Williams [this message]
2021-03-30 17:54 ` Jason Gunthorpe
2021-03-30 19:00 ` Dan Williams
2021-03-30 19:26 ` Jason Gunthorpe
2021-03-30 19:43 ` Dan Williams
2021-03-30 19:51 ` Jason Gunthorpe
2021-03-30 21:00 ` Dan Williams
2021-03-30 22:09 ` Jason Gunthorpe
2021-03-30 2:47 ` [PATCH v2 3/4] cxl/mem: Do not rely on device_add() side effects for dev_set_name() failures Dan Williams
2021-03-30 2:48 ` [PATCH v2 4/4] cxl/mem: Disable cxl device power management Dan Williams
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