From: Kimberly Brown <kimbrownkd@gmail.com>
To: Stephen Hemminger <stephen@networkplumber.org>
Cc: Michael Kelley <mikelley@microsoft.com>,
Long Li <longli@microsoft.com>,
Sasha Levin <Alexander.Levin@microsoft.com>,
Stephen Hemminger <sthemmin@microsoft.com>,
Dexuan Cui <decui@microsoft.com>,
KY Srinivasan <kys@microsoft.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 3/3] Drivers: hv: vmbus: Fix race condition with new ring_buffer_info mutex
Date: Thu, 28 Mar 2019 00:30:57 -0400 [thread overview]
Message-ID: <20190328043057.GA2258@ubu-Virtual-Machine> (raw)
In-Reply-To: <DM5PR2101MB091851BC7C55093D388514D9D7420@DM5PR2101MB0918.namprd21.prod.outlook.com>
On Thu, Mar 21, 2019 at 04:04:20PM +0000, Michael Kelley wrote:
> From: Kimberly Brown <kimbrownkd@gmail.com> Sent: Wednesday, March 20, 2019 8:48 PM
> > > > > Adding more locks will solve the problem but it seems like overkill.
> > > > > Why not either use a reference count or an RCU style access for the
> > > > > ring buffer?
> > > >
> > > > I agree that a reference count or RCU could also solve this problem.
> > > > Using mutex locks seemed like the most straightforward solution, but
> > > > I'll certainly switch to a different approach if it's better!
> > > >
> > > > Are you concerned about the extra memory required for the mutex locks,
> > > > read performance, or something else?
> > >
> > > Locks in control path are ok, but my concern is performance of the
> > > data path which puts packets in/out of rings. To keep reasonable performance,
> > > no additional locking should be added in those paths.
> > >
> > > So if data path is using RCU, can/should the control operations also
> > > use it?
> >
Hi Stephen,
Do you have any additional questions or suggestions for this race
condition and the mutex locks? I think that your initial questions were
addressed in the responses below. If there's anything else, please let
me know!
Thanks,
Kim
> > The data path doesn't use RCU to protect the ring buffers.
>
> My $.02: The mutex is obtained only in the sysfs path and the "delete
> ringbuffers" path, neither of which is performance or concurrency sensitive.
> There's no change to any path that reads or writes data from/to the ring
> buffers. It seems like the mutex is the most straightforward solution to
> preventing sysfs from accessing the ring buffer info while the memory is
> being freed as part of "delete ringbuffers".
>
> Michael
next prev parent reply other threads:[~2019-03-28 4:31 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190122020759.GA4054@ubu-Virtual-Machine>
2019-02-22 3:46 ` [PATCH v2 0/2] Fix a race condition vulnerability in "_show" functions Kimberly Brown
2019-02-22 3:47 ` [PATCH v2 1/2] Drivers: hv: vmbus: Refactor chan->state if statement Kimberly Brown
2019-02-24 16:54 ` Michael Kelley
2019-02-22 3:47 ` [PATCH v2 2/2] Drivers: hv: vmbus: Add a channel ring buffer mutex lock Kimberly Brown
2019-02-24 16:53 ` Michael Kelley
2019-02-26 6:24 ` Kimberly Brown
2019-03-14 20:04 ` [PATCH v3 0/3] Drivers: hv: vmbus: Fix a race condition in "_show" functions Kimberly Brown
2019-03-14 20:05 ` [PATCH v3 1/3] Drivers: hv: vmbus: Refactor chan->state if statement Kimberly Brown
2019-03-14 20:05 ` [PATCH v3 2/3] Drivers: hv: vmbus: Set ring_info field to 0 and remove memset Kimberly Brown
2019-03-29 16:01 ` Michael Kelley
2019-03-14 20:05 ` [PATCH v3 3/3] Drivers: hv: vmbus: Fix race condition with new ring_buffer_info mutex Kimberly Brown
2019-03-14 22:45 ` Stephen Hemminger
2019-03-17 1:49 ` Kimberly Brown
2019-03-20 20:06 ` Stephen Hemminger
2019-03-21 3:47 ` Kimberly Brown
2019-03-21 16:04 ` Michael Kelley
2019-03-28 4:30 ` Kimberly Brown [this message]
2019-03-28 18:42 ` Stephen Hemminger
2019-03-29 16:04 ` Michael Kelley
2019-04-10 22:59 ` [PATCH v3 0/3] Drivers: hv: vmbus: Fix a race condition in "_show" functions Sasha Levin
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